Dave Richards AA7EE

December 30, 2014

New Source Of Resonators For 40M

Yesterday, Joel KB6QVI, tipped me off to a new source for ceramic resonators that look as if they should be a godsend for anyone building a simple QRP rig for the phone portion of 40M (such as VK3YE’s Beach 40) – that’s if they perform according to specifications.  A while back, we both bought some Murata resonators with a specified frequency of 7.2MHz, only to find that the very highest frequency they would oscillate at was 7.15MHz. Cecil K5NWA runs an online parts site called The Parts Place, and is listing a 7.28MHz resonator. The description says,

“Tunes over a wide frequency range. With 100 pf capacitor a shift of 7036KHz – 7284KHz is expected – will verify when parts arrive, do not use the center pin.

Note that for a lower top frequency, put a fixed small polystyrene capacitor in parallel with the adjustable capacitor, which can be made smaller.”

Joel and I ordered 20 each, and Patrick W9PDS said that he was going to purchase some as well. When Joel first found them, there were 167 available – there are now 127* as I write this.  They are 30 cents apiece, 22 cents if you buy 10 or more, so it would seem worth picking up a few for the parts bin, as resonators that are usable in the upper portion of 40m don’t come along too often. The last time we found good ones was from hamshop.cz, and they have been out of stock for months now.

Please note that we haven’t yet received ours and don’t know whether they will resonate reliably within a usable range of frequencies but for home-brewers, this is worth a try while they’re available. If they are indeed usable, let’s hope that Cecil is able to get more in once the current lot is sold out. Incidentally, Cecil’s site is easy to use. I received e-mail status updates to verify that the order had been received, then another one to verify that payment had been received, and another one to notify that the order had been approved – all in short order. I assume that there will be another when the order has shipped. With a business like this, being run by an individual ham, this level of notification already surpasses what I would expect.

My soldering iron hasn’t been seeing much action lately, but Joel is an inspiration at the workbench; I have lost track of the sheer number of projects he has put together since I have known him. Doubtless he will verify that these are usable for ham applications once his arrive and I’ll post the results here once that happens. If I happen to put one of mine into a test circuit, I’ll let you know what happens with that too

Here’s the link once again (opens in a new window), and thank you to Joel for bringing this to our attention.

*As of 16:25 UTC (8:25am PST), there are now just 88 available.

NOTE – Steve G1KQKH, in the comments below, noted that this same resonator is available from Mouser. Check the comments section for his link to UK Mouser. If you’re in the US, the link is here (opens in a new window).

December 7, 2014

Thomas Witherspoon K4SWL Joins The Friends Of The Shortwaves!

I just knew that at some point, Jeff K1NSS would include Thomas Witherspoon, K4SWL in his Friends Of The Shortwaves series on Dashtoons. It was a no-brainer. Thomas’ blog, The SWLing Post has a very strong following and Thomas continues, through the blog, to make a strong case for the continued use of shortwave broadcasting the world over, and to support the interests of shortwave listeners.  He also hosts an online archive of shortwave recordings at The Shortwave Radio Audio Archive. If that wasn’t enough, as founder and director of the charitable organisation Ears To Our World, he puts self-powered shortwave radios into the hands of people in areas of the world that are under-served by the forms of mass media communication that we enjoy in the developed world. Thomas doesn’t just talk the talk – he walks the walk as well.

If you need the services of an experienced and talented artist who also “gets” the ham community (as he is himself a ham), you should seriously consider Jeff Murray K1NSS. Many people have used his services, and you’ll see many examples of his work at Dashtoons.

November 23, 2014

Videos Of The Sproutie Regen In Action

Many apologies for taking so long to get these videos up. The only camera I have that can do video is so old and gives such poor quality video, that it’s a little tough for me to feel inspired in that direction.  I do like to put quality still pictures on my blog, and am currently unable to do justice to my projects when it comes to videos.  However, even a low-res video can still give you an idea of how a receiver handles that no amount of still pictures can, so last night and this morning, I made a few brief videos, and here they are. I would recommend viewing them on this page rather than on YouTube, simply because there is no point in seeing the larger version on YouTube – the video resolution simply isn’t there. Aaron N9SKN is building a Sproutie, and asked if and when I was going to post videos. His request gave me the final push/feeling of guilt that was needed to get me moving!

Here’s The Sproutie receiving CW and SSB on 20M (with the coil that tunes from 12100 – 14400KHz) –

and here it is receiving AM stations on the 60M and 49M BC bands (with the coil that tunes from 4810KHz – 6320Khz) –

As the main blog-post on The Sproutie shows, I have coils for continuous coverage from about 3MHz up to 16MHz (as well as a coil for 2.1 – 2.7 MHz) and have wound temporary coils that worked up to 24MHz. It will probably work even higher. I have even read reports of Nicky’s TRF (which is the circuit I used for The Sproutie’s front end) being used successfully on the 10M amateur band!

The original blog-post giving construction details of The Sproutie is here.

September 16, 2014

New “Free” SA602 and SA604 Offer Back – Now With Overseas Shipping

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 6:29 am
Tags: , , ,

On Saturday, a medium size Priority Mail flat-rate box packed full of IC’s, resistors, transistors and other devices arrived from KV7L. Lynn is the gentleman who made my previous SMT SA602 and SA604 offer possible by shipping me 2 large rolls of SMT SA602’s and SA604’s a few months ago. At a rough guess, that initial shipment contained about 1700 SA602’s and a few hundred SA604’s. Almost all of them went to QRP clubs wishing to sell them to raise funds, people organizing group builds, and the parts bins of individual home-brewers – and all for $4 to cover just the cost of shipping and the Paypal fee.

Now I have another, final shipment from Lynn and can open up this offer again. As well as the SMT 602’s and 604’s, Lynn threw in some bags of 2 and 3 W resistors, some of which will be useful for making QRP dummy loads, as well as some voltage regulators, power MOSFETS, and small signal NPN transistors. A number of people did ask if I could ship overseas, to which I replied that I was trying to keep the distribution process simple (for me) by limiting it to the US only. This time around, I’ll open it up to other countries, though the shipping costs are significantly higher and I’m not sure whether it will be considered worthwhile to those not in the US.

Sprat The QRP Cat wasted no time in thoroughly smelling all the parts. Lynn has dogs so I’m sure there was plenty for Sprat to sniff –

Before detailing the new deal (boy, I feel a little like FDR :-) ), there was something else I wanted to mention. Lynn KV7L said to me on the phone that he’d really like to receive QSL’s from some of the home-brewers who have had some of the parts from him so he can get an idea where his parts are ending up. Although I wasn’t shipping overseas in the last round, one gentleman in India asked if I could ship to a friend in the US who was visiting him in Bangalore in the near future and could deliver the parts. He is an educator who will be using his 602’s to encourage his students to build something. Lynn said he’d love to have a QSL from India, and from all the other places his parts are going so that he can put them up on his wall and get an idea of how his parts are being distributed far and wide.  This is not about tracking them – it’s because Lynn’s only involvement  in this giveaway has been to very kindly ship the parts to me, while I distribute them. He is a bit disconnected from the process and being able to look at QSL’s on his wall will help him feel a bit closer to the whole “free parts” operation. If you have already received parts from him (through me), I know that he’d love to receive a QSL from you. You can either send it to him, or to me – and I will forward it on to him. Both of our addresses are good on QRZ. Lynn’s address is a PO Box, while his actual QTH is in a fantastic radio location. He is miles from his nearest neighbor in rural Eastern Oregon,  and not served by any utility (he is 100% solar-powered). He has 5,000 feet of wire buried in the earth for a ground and his resulting noise level is very low indeed. He is the co-net manager of the Noontime Net on 7268.5KHz daily. It’s a regional net that covers most of California, Oregon and Washington, as well as a few other nearby states when daytime conditions are good and it seems that Lynn, with his fantastic radio location, hears almost everyone who calls into the net.

If you haven’t yet taken advantage of this offer and would like to, please know that Lynn would love to receive a QSL from you as well.  I think it’s a very modest request from a gentleman who has shipped me something like 2,300 SMT SA602’s and 600-800 SA604’s and asked for nothing in return, other than the occasional update on how the giveaway is going. If you don’t have a QSL then don’t worry about it – and please don’t let it deter you from taking advantage of this offer.

This time around, as well as SMT SA602’s and SA604’s, I have a bunch of 1 and 2 watt resistors in low values, some of them suitable for building QRP dummy loads. There are some 160 ohm resistors and some 130 ohm ones. 2 x 160 ohm and 1 x 130 ohm resistor, all in parallel will give you a total effective resistance of 49.5 ohms. If all 3 resistors are 2 watts, then the final dummy load will handle about 6 watts, which is more than enough for the QRP “full gallon” of 5W. Some of the resistors are 1W, and even if you were to use just those, your final dummy load would still handle 3W,  There are also other values of 1 and 2W resistors such as 22 ohms, 27 ohms, and also 51 ohms. I don’t have many of the 51 ohm ones, so you’ll probably only get one of those, but there are more available of the other values.  Actually, the 51 ohm 2W resistor would make a useful dummy load on it’s own. It should handle 5W for very short periods and of course, if your TX is just 2W, it will be even more able to handle long key-down periods. If you want to make a “classic” QRP dummy load, you can mount your decided combination of resistors in a mint tin, along with a BNC connector for connecting it to your TX and you’ve got yourself an affordable and useful station accessory.

I also have some LM2575T 12V 1A voltage regulators, in a 5-lead TO-220 package. Datasheet here. There are also some F10P03L P-channel power MOSFETS, datasheet here, as well as some PN4275 NPN switching transistors, for which the datasheet is here.  I may throw in a few general purpose NPN transistors too, if I have any left. They have the number F15103477844 printed on them which I haven’t been able to find any datasheets for but that is not surprising. It is very common for mass-manufactured electronic goods to use parts with parts numbers that were supplied specifically for one production run. They are small signal NPN transistors and they may well be very similar to transistors used in many other products, that had different numbers stamped on them. They’ll most likely work fine in many circuits that call for 2N3904’s, BC109’s or similar.

This photo isn’t exactly what you’ll get in your package, but it’s pretty close. You’ll probably get this, along with a few extra resistors and possibly some extra transistors thrown in. As a bare minimum, you’ll get 15 x SMT SA602’s, 6 SA604’s, an assortment of 2 and 3 W resistors in low values, some of which will be suitable for making up QRP dummy loads, 8 x LM2575T 12V 1A voltage regulators, 6 x F10P03L P-channel power MOSFETS, and a small handful of PN4275 NPN transistors –

My supplies of both 602’s and 604’s are now limited but if you need a few extra for a club project or group build, please ask and I’ll try to accommodate you. The 602’s are particularly limited, but I have a few more of the 604’s, so if you have a group project that uses 604’s, I should be able to provide them.

The last offer was just for 602’s and 604’s and for that I was asking $4. To ship these I need a small box, (as opposed to the padded mailer used previously), which costs a bit more, and the extra weight costs a bit more in shipping, I am now asking $6 payable via Paypal for US builders – and also asking if you can send KV7L a QSL card (either directly to him, or to me so that I can pass it along to him – but don’t write it out to me – write it to Lynn KV7L). If you don’t want to use Paypal, you can mail a check for $5.50 (because I don’t have to pay the Paypal fee) to me. This is quite a handy way to do it, as you can include your QSL card for Lynn in the envelope with the check :-)

Whatever you do, don’t send any money until you have first e-mailed me! My e-mail address on QRZ is good, or you can use mycallsign@arrl.net

If you are anywhere in Europe I will now ship to you, but the shipping costs are significantly higher, I’m afraid.  If you are in Europe, I need to ask for US$17 to cover the shipping box, shipping costs and the Paypal fee. I’d rather not accept personal checks from outside the US, so will have to ask for Paypal for non-US builders, to keep the process relatively simple for me. However, if you are outside the US and are able to mail a QSL card to Lynn (either to Lynn, or to me – but make sure it is written out to Lynn) I will be happy to reimburse you for the postage via Paypal. I’d really love for Lynn to get a whole bunch of QSL’s from many different areas. He’ll love that. In fact, if you’re a US builder who is paying via Paypal, let me know if you plan to send a QSL and I’ll knock 50 cents off the price to cover most of your postage.

If you are outside the US and Europe, I may well be able to ship to you, but will have to get a quote from my local Post Office. It will probably be very close to the price for EU. E-mail me if you seriously intend to take advantage of the offer and I’ll get a price for you.

I hope that all made sense, and that the parts make it worth the expenditure of a few dollars for the shipping. It’s a no-brainer for US builders, and may be worth it to non-US home-brewers too.

 

73 for now,

Dave  AA7EE

PS – I have 100 of these Molex connector shells. The total width is 1  1/8″  (1.125″). Let me know if you’d like some of these too, but you have to ask as I know that most people won’t want them.

Update (Sep 18th) – I am out of all the transistors and the voltage regulators but do still have a few SA602’s, resistor packs, and plenty of SA604’s left. At this point, I can still make up a package for you containing SA602’s, SA604’s and the resistor pack. Prices are the same (as the shipping is very nearly the same).

Update (Sep 22nd) – I have a good amount of SA604’s left, a few SA602’s, and the Molex connectors. Everything else is gone.

Update (Sep 24th) – All that is left is the SA604’s and the Molex connector shells.

August 30, 2014

SA602 and 604 Giveaway Update, and SA604 Circuits

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 6:04 pm
Tags: ,

I’ve had a busy few days. Since posting details of the reels of SMT SA602 and SA604 IC’s that a very generous ham sent to me with a request to distribute them to other homebrewers and building groups, I’ve been spending quite a lot of time cycling to and fro between my house, the local print and copy shop (for supplies of padded mailers), and the Post Office. The first day’s worth of envelopes looked like this just before being bundled into my backpack for the short trip to the Post Office (names and addresses inexpertly blurred out in order to protect the identities of the innocent) –

I mailed out 18 packets on the first day, and almost as many the next day. Most went to individual builders and experimenters, though a few did go to groups for group builds. The response has been very encouraging. I wasn’t too sure how many people would be interested in SMT parts but it seems that quite a few folk do indeed experiment and build with them – and they are not all young ‘uns either. One gentlemen who requested a set is 83 years old. Excellent! With the help of breakout boards, like W1REX’s MePADS, or these ones from OSH that Sanjay KI6VFH told me about (only $1.50 for 3, including shipping), once you’ve got the device mounted to the pad, building Manhattan-style with these IC’s is straightforward. Incidentally, the boards from OSH are SO-8, so will work for the 602’s but not the 604’s, which are SO-16. Also, Rex’s pads can be glued straight onto a copper substrate as there are no contacts on the flipside, while the OSH one will need to be suspended above the copper groundplane with short, stiff ground leads. Perhaps someone has posted a design for an SO-16 breakout board on OSH?

Standing in line at the Post Office has it’s good sides, one of them being the notices that I spotted attached to the plexiglass divider at the customer service counter –

As I thought would be the case, everyone wants the 602’s. I was expecting only a few people to also want 604’s but as it turns out, a majority are also asking for a few of them. Many don’t yet know what they will do with them but are hoping to find a worthy project. A few actually have projects planned. One gentleman is planning a group build with his club, in which they will build pagers. I didn’t ask for more details on what the frequency of operation will be, but I am curious. Another is going to build a weather satellite receiver.  Paul K0EET mentioned that 604’s turn up in home-brew spectrum analyzer projects as an IF strip and a logarithmic RSSI (to drive the y axis).  He also told me about an article in the July 1993 issue of QST by OH2GF for a synchronous AM detector using an SA604 and a couple of 602’s. It is designed for receivers with an IF of 450-455KHz, so would be a great addition to many existing shortwave receivers. Thanks Paul (makes mental note to remember this project). In it’s application as a Received Signal Strength Indicator (RSSI) it could also be used as an S-meter for a direct conversion receiver (a quick Google search should get you a circuit).

So quite a few circuit ideas for the SA604. The application sheet also shows how, with an SA602, you can make a simple FM receiver. Personally, I can see wanting to try it out as a synchronous detector for AM signals at some point.

Oh – one idea for the 602’s which I thought was very novel, was one gentleman who plans to rip out the guts of his HW-8 and replace them with a DDS-tuned superhet. Cool!

I started out with quite a large reel – bigger than shown in the picture of Sprat The QRP Cat performing QC. By the time I took that picture, several hundred had already gone out to various experimenters and builders. With the encouraging response to these posts, I will probably run out soon. Not to worry though, as the gentleman who sent them to me still has some left that he has promised to send. I am not sure when those will arrive, but I’ll post updates to this blog. I don’t think it will be very long.

If you build something cool with these chips, please let me know!

NOTE – SA602 and 604 offer on hold until further notice. I’m almost out, but the very kind gentleman from Oregon who sent me this batch has some more he will be sending soon. I will make a new post to this blog when I have more IC’s in stock.

August 26, 2014

Free NE602’s and 604’s

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 8:29 pm
Tags: , , ,

It’s been on my mind to make this post for quite a while now. Some time back, a very generous ham in Oregon gave me a sizeable quantity of SA602 and SA604 SMT IC’s. They were part of a production run that didn’t materialize. He got a deal on them and has been hanging onto them ever since. Now he would like to pass them on (for free) to other home-brewers, so he asked me to help out. He wants them to go into the parts bins of people who may well use them, and does not want them to go to people who will merely resell them for a profit. He’s perfectly OK with them being used for a club group build, or a club kit designed to raise funds for a QRP club – just not in large quantities to individuals who will turn around and sell them. The idea is to encourage people to build something.

I’m sure you know all about the NE602/SA602/NE612/SA612 oscillator and double-balanced mixer IC. It has, of course, been used in countless numbers of simple direct conversion receivers such as The Sudden. It’s not ideal in the front end of a receiver, being very susceptible to overload in that usage, but it sure does make it easy to build a very simple DC receiver.  It can be used to good effect as the 2nd mixer in a receiver, and as a balanced modulator. In any application where the input levels are within certain defined limits, it performs well. The SA604 is a low-power FM IF chip. I’ll leave you to do the research and check out the datasheets.

Oh – and these IC’s have been through rigorous quality control. Here’s Sprat The QRP Cat checking the roll of SA602’s. They passed the test :-)

Sprat The QRP Cat performing quality control on the roll of SA602’s.

The SA602’s are in an SOIC-8 package and the SA604’s in an SOIC-16 package. Here is one of each, placed on a sheet of W1REX’s MePADS –

Jason NT7S built a really neat SSB rig based around an Si5351 PLL/VCXO chip. He used 2 of these SA602’s as part of the design. you can read about (and see) Jason’s “Simple SSB” rig here. He describes the rig’s architecture in an earlier post here. It’s great stuff and very much in the spirit of ham radio.

I don’t want to make any money from this, but would like to cover my expenses, so I will charge a small fee to cover the cost of a padded mailer, postage and the Paypal fee. Here’s the deal. If you are an individual home-brewer in the continental US who could use some of these SA602 SMT IC’s (which are exactly the same as NE602’s), send me an e-mail – either to my e-mail address on QRZ, or to mycallsign@arrl.net to let me know you’re interested. I’ll reply to let you know what e-mail address to Paypal the money to. For $4, I’ll send you 15 SA602 IC’s. If you’d like some SA604’s as well, let me know but please only ask if you think there’s a chance you might use them.  If you would like a larger quantity for a club kit or group build, send me an e-mail with the info and I should be able to help you out.

Oh – and unlike my recent variable capacitor give-away, I have quite a lot of these, so you don’t need to be the first (or even the 20th or 30th) person to reply. As not too many builders use SMT, I suspect this offer will be available for a while.

I am very grateful to the gentleman in rural eastern Oregon who is the reason for me to be able to spread this little piece of home-brew goodwill!

NOTE – to the gentlemen who left comments, I have deleted them. It occurred to me that having your e-mail addresses and info in the comments section might cause some enterprising scammer to pretend he/she was me and ask you to send the money to them. Having said that, they would have to be pretty desperate to go to all that trouble to make an extra $4!  Best to e-mail me at my e-mail address on QRZ, or to mycallsign@arrl.net

NOTE – SA602 and 604 offer on hold until further notice. I’m almost out but the very kind gentleman from Oregon who sent me this batch has some more he will be sending soon. I will make a new post to this blog when I have more IC’s in stock.

 

August 25, 2014

A Huge Compliment From Dashtoons – And A Variable Capacitor Offer

I’m sure you’re familiar with Jeff Murray K1NSS. He’s the man behind Dashtoons, those ever-so-creative and mirth-inducing ham radio cartoons and funnies that appear on many a happy ham’s QSL card and in print, on websites – in fact, wherever a good clean piece of chuckle-creating ham radio artwork is needed. Jeff is well-known within the ham community (and he drew comic strips for print publications in the past) so seeing this today, fresh from Jeff’s pen and creative mind had me, as my fellow Brits say, truly gobsmacked (in a good way). It got such a laugh from me, as it came just a day or two after I had referred to myself as an old coot in the Ham Radio Operators group on Facebook –

One of the things I love about this image, is that it could almost be an ad out of a magazine taken straight from the 50’s. The typefaces, the layout and the wording are all reminiscent of print ads from the middle of the 20th century – yet the design is not solely mid-century. There is something contemporary and clean about it as well, and it is obviously executed with modern tools. Great stuff!

Jeff’s site is here and it’s well worth a look, if you haven’t had a gander at it yet (as some of us Brits are wont to say). I’m even featured on his home page for the time being. Aww shucks! Jeff is available for commissions, is surprisingly affordable and although I haven’t asked him, perhaps he wouldn’t mind drawing or designing non-ham things for you if you have the need? You can always ask. Thank you Jeff – you’re the best!

 

Now on a different tack, I have a couple of air-spaced variable capacitors that are surplus to my requirements. I’d like to pass them along to someone who can use them, for the price of shipping. They have ceramic insulators and what look like aluminum plates. They wouldn’t be ideal for VFO’s, due to the single bearing and the aluminum plates, as opposed to the double-bearings and brass, or nickel-plated brass that are preferred for very high stability circuits. Also, the bearings in them have quite a bit of friction, even when lubricated. There are actually no bearings in these variable capacitors. From what I can tell, the spindle and the frame around it are in direct contact with no bearings. The spindles do turn and the rotation is smooth, but there is a fair amount of friction. It can be a little hard to turn the spindles by hand but when you put a knob on them, they rotate with no problem. They are identical, with a maximum capacitance of 140pF each. The best way I can think of to describe the rotation is “smooth, yet with a fair amount of friction.”

Although these would not be ideal for the main tuning on a receiver or transmitter, I’m thinking they would work well in a situation where they could be set and left – where they were being used like trimcaps. They’d be great for the trimcaps at the base of an antenna, where they could be set once and left. If you put a knob on them, adjusting is not difficult at all – it’s just that they don’t have that silky smooth feel you’d want for a tuning control. I’ve done my best to describe them accurately and will mail them anywhere in the continental US for $3 (preferably via Paypal) for both of them. That should cover the shipping and the Paypal fee. Please don’t ask if you’re outside the continental US – I’d like to keep this quick and simple.  In case there are several people wanting these, don’t send any money until I tell you. Send an e-mail first to let me know you want them – I’m good on QRZ. If you leave a comment under this post, that will work too, as the system will send me an e-mail notification.

I know they’re only a couple of parts, but I don’t like having components lying around that I know I’m not going to use.

That’s all for now, as The Sproutie is calling and I have some listening to do :-)

EDIT – The variable capacitors are spoken for. Sorry about that!

 

August 21, 2014

The Sproutie – A General Coverage Regen Receiver with Plug-In Coils

NOTE – Many thanks to Aaron N9SKN and Cliff WA9YXG, who pointed out errors in the schematics. They have been corrected, and N9SKN has built a working Sproutie from the schematics in this post so rest assured that if you follow them, you can too.

Aaron N9SKN has put together a parts list. For those builders who like to work from one, he will send it to you, or you can contact me. Both of our e-mail addresses are on QRZ. If you don’t have access to the QRZ database, then leave a comment at the end of the blog-post, and I will send it to you. Alternatively, you can e-mail me at mycallsign@arrl.net (substitute AA7EE for the word “mycallsign”, of course!)

If you’re thinking about building this great little general coverage regen, I’d urge you not to print out any of this article to work from. The reason is that whenever I make an improvement or addition to this receiver, I edit this article. By working from a printout, you’ll be missing out on any changes I subsequently make. Having said that, The Sproutie works fine as is, so don’t be scared off from building it.

I’ve mentioned before in posts how one of my first shortwave receivers as a teenager growing up in England (in fact, possibly the first) was a one tube battery-operated regen built from a kit. Many of the popular electronics magazines at the time, including my favorite, Practical Wireless, carried advertisements from a company called H.A.C. (“Hear All Continents”) who sold kits for simple HF regenerative receivers. This was the ad I remember best. To the teenage me, this receiver was the holy grail. With this receiver, there would be no stopping me. I would be the king of the hill, if only I could have this magnificent shortwave receiver –

Ads like this for H.A.C. shortwave receiver kits were common in the UK up until the early 1980’s. Image taken, with permission, from Louis Meulstee at http://www.wftw.nl/

I saved my pennies and eventually sent off for the H.A.C. Model DX Mk. 2. It wasn’t as fancy-looking as the one picitured in the ad, as it didn’t have a front panel or a calibrated dial but hey – those kinds of regens were only for the truly well-heeled, and I was just a kid with a modest allowance. The kit that arrived used an HL23DD valve (or equivalent). It was a battery operated double diode triode, with a coated filament, to maximize emission on the low operating voltage of just 1.5V (2V maximum, with a current consumption of just 50mA). This set didn’t have a front panel or a calibrated dial, sporting just a modestly-sized aluminum chassis with 3 chicken head knobs on the front, but with my 2000 ohm headset and 90V high tension battery, I truly was the king of the shortwave hill. I don’t have any pictures of my H.A.C. Model DX Mk. 2, but featured here are pictures of someone else’s taken from Louis Muelstee’s great website, which is where the ad shown above came from too.

The H.A.C. Model DX Mk. 2 cost me all of £14.50 in the late 70’s. (Photo taken by Philip McNamara and taken, with permission from Louis Meulstee at http://www.wftw.nl/)

This one tube regen used an HL23D double diode triode tube with low current consumption 1.5V filament. The blue lead on the left leads to a connector that plugged into a 90V high tension battery. (Photo taken by Philip McNamara and taken, with permission from Louis Meulstee at http://www.wftw.nl/)

Truth be told, this wasn’t exactly the most sensitive receiver ever created, but it mattered little to a teenager in England in the 1970’s, with plenty of loud shortwave broadcast signals. There was much to keep those high impedance headphones firmly glued to my head. They were fairly cheap quality, and the way the metal headband tensioned the earpieces against my ears made them a little red after 30 minutes of use. Did I care? Not at all – I wore them for hours on end, as I was enthralled by the sounds of Radio Nederland, Radio Prague, Radio Tirana Albania, Radio Moscow, The BBC World Service and many other broadcasters, as well as all the weird-sounding utility stations and the very mysterious numbers station from East Germany. I had no idea back then what it was, but the female voice announcing strings of numbers in German was strangely compelling. Every day, I would rush home from school, eager to get into my bedroom, plug the low-tension battery in, wait for a short while for the tube filament to heat up, then connect the high tension battery and clamp the headphones to my head, cup of tea by my side, as another listening session began. Weekends were heaven. As soon as all my homework was out of the way, there was nothing but blissful hours and hours of potential shortwave listening time stretching ahead. From time to time, the 90V battery would run down, and I would walk the 2 miles into the village of Astwood Bank to buy a new one from the local gas station.  It didn’t take me long to figure out how to power the filament from a transformer in order to save money on low tension batteries. I eventually figured out how to do the same for the high tension supply too. On good days, I could even pick up some local amateurs on 80M SSB. Man, I was indeed the king of the shortwave hill! At the back of my mind, though, was the idea that somewhere out there was still a truly dreamy shortwave receiver – one that had a front panel fashioned from a sheet of aluminum, and a calibrated tuning dial. It only took me until the age of 50 to finally own one of those only-in-your-dreams kind of receivers.

Which is what this blog-post is all about.

I’ve had some encouraging success with regens recently. Both the WBR and my modified version of the the WBR, which I built for the 31M BC band, worked well, with no common-mode hum, instability, or any of the other kinds of naughtiness that sometimes accompany the operation of regenerative receivers. There was one main thing about the WBR’s that limited them for me, and that was the fact that they only operated on a limited range of frequencies. After building these 2 receivers, the next logical step was to build a general coverage regen with plug-in coils. I wanted a set that was built solidly, with a reduction drive and a calibrated tuning scale, so that I could prove to myself something that I already knew – that a regen, properly constructed, can serve well as a shortwave receiver rather than just as a novelty, which seems to be the category most people have placed them into these days. I’m reminded of a comment on a discussion forum I saw recently, in which a gentleman was talking about a regen he had built once. It was sensitive, received lots of stations, and gave him much enjoyment, he said, but he never really knew where he was on the band. “Well of course you didn’t!” I thought to myself, “but that’s not because it’s a regen – its because when you built it, you didn’t build it with a calibrated dial. It’s not the regen’s fault you didn’t know where you were on the band – it’s yours!”

Charles Kitchin had a design for a receiver which caught my attention. It was published in the Feb 2010 edition of CQ Magazine and consisted of an oscillating detector feeding a 2-stage amplifier consisting of a low-noise FET-input opamp acting as the preamp. The preamp had a low-pass filter with a variable cut-off point, as well as an extra capacitor in the audio chain that could be switched in to give a nice lift to the lower frequencies, for those times when you have a nice strong signal and want a bit of bass boost. This preamp drives an LM380, which makes for a much lower noise AF amp chain than the default in these types of receivers that employ an LM386. On top of that, there is provision for a line out jack for recording. I was interested – regardless of the front end I used, this could definitely be the AF amp for a “serious” regen!

Before I had even fully decided on the finer details of this project, I assembled the AF amp on a separate board. I wanted this to be a somewhat modular receiver, with the AF and RF sections built on different boards so that if either section didn’t work out, I could try a different one. I wasn’t entirely convinced that the value of Hammarlund tuning capacitor that I was planning on using was going to be ideal, so I wanted it to be a relatively easily swappable part with other tuning capacitors of different value but with the same form factor (of which I own a few). If I was going to go to the trouble of building something like this on a nice chassis, I wanted to give myself the maximum possible chance of succeeding.

Here is the schematic of the AF board. It is a little different from the version originally designed by Mr Kitchin (though not by much) as I will explain –

In Chuck’s original version, the 2.2K resistor on the input was 5K.  The ratio of this value to the value of the 100K resistor between pins 2 and 6 of the AD820AN determine the gain of the stage, and I wanted a bit more. Also, the LM380 was motorboating when the AF gain pot was set to anything higher than half-volume, so I added the 10 ohm resistor in the supply line and bypassed it with a 470uF electrolytic, which stabilized it nicely. Another small issue I experienced with mine was that when the AF gain pot was at absolute maximum volume, rotating the low-pass filter pot caused clicks and “bloops” in the speaker. It seemed to only happen when the slider of the pot had finished traveling over the carbon track and had actually made contact with the metal that formed the hot end of the control. I didn’t know what caused this, and I suppose it’s a bit of a “kludgy” fix, but I reasoned that placing a low value resistor at the hot end of the pot would, in effect, prevent the amp from being driven at absolute maximum volume but that the difference between this level and the absolute maximum volume would be so small as to be barely noticeable. I tried a 10 ohm resistor, which reduced, but didn’t completely eliminate the clicks and bloops. A 47 ohm resistor did cure it though, and I was left with a volume control that operated smoothly, and a variable low-pass filter pot that also operated smoothly. Very satisfying! Finally – about those 2 capacitors marked CT. They are coupling capacitors that help to determine the amount of low-frequency signal that is passed. In N1TEV’s original design, they were both 2.2uF, and I found these values to be a bit high for my tastes, making the audio a bit too bassy. This is all a matter of personal taste of course. I used 0.22uF for CT in both positions and found that it gives a pleasing lift to the lower frequencies. It is not always apparent on the internal speaker (in which case a higher value would be better), but is more noticeable when using good quality earbuds or headphones, and on recordings. Use whatever values work best for you. The 0.1 and 0.01 uF bypass capacitors on the 12V line were placed so as to bypass the 12V supply directly at the point of entry into the chassis. I wasn’t experiencing any problems before fitting them but it can’t hurt to decouple the power supply the very moment it enters the enclosure can it? Nip these things in the bud before they even have a chance to get a foothold, I say :-)

Here’s the AF board as I first built it, before changing the 5K resistor on the input to a 2.2K resistor, and the two 2.2uF capacitors to 0.22uF parts – and before adding the 10 ohm resistor in the 12V supply line and the 470uF capacitor to bypass it. The lengths of lavalier mic cable for the variable low-pass filter and the AF gain potentiometers have already been soldered in place, and they exit through holes drilled in the board. The headphone jack and DC power connector are temporary, for the purpose of testing. The Manhattan pads are of course, as always, W1REX’s MeSQUARES and MePADS

The front end is a very standard design. It is the same configuration (and indeed the same circuit) as used in the WBR, with the exception that the tank (unlike that in the WBR) is unbalanced. This same arrangement was used in Nicky’s TRF, as featured in issue 70 of SPRAT, and I believe the original circuit was developed by GI3XZM. I wanted this receiver to be usable over a wide range of frequencies, and in keeping with my “modular” approach, wanted the receiver to be as versatile as possible. A plug-in coil system, with both gangs of a dual gang variable capacitor, as well as the fine tuning capacitor, all available at the pins of the coil base, allows for a lot of flexibility when winding coils for different bands. The user decides, when constructing a plug-in coil, whether to include padding or series capacitors for the main tuning and fine tuning capacitors, as well as choosing whether to use one, or both gangs of the tuning capacitor. In this way, with some calculations and a bit of trial and error you could, say, wind a coil to cover a large segment of the HF spectrum, or a single narrow band of frequencies. If, after some listening, I decide one day that I am particularly interested in the 16M broadcast band, I can construct a coil to cover just that one band. Neat! EDIT – I just did construct a coil for the 16M band (Feb 2015)

The J310’s in the RF amp and the detector stage could be any similar N-channel JFET such as the MPF102 or the 2N3819. Likewise, the two 2N3904’s could be most any small signal general purpose NPN transistor. I originally fed the output of the J310 “infinite impedance” detector stage directly into the input of the AF amp board, but quickly discovered that the gain wasn’t enough to comfortably drive a loudspeaker. Had I done a few quick calculations beforehand, I would have realized that. I wanted to take advantage of the fact that the output chip is an LM380, by driving it enough to make a loud noise into the speaker! Adding the single 2N3904 preamp stage after the detector solved the problem nicely. I have built enough of these simple receivers that can drive “a small speaker to a comfortable volume in a quiet room” :-) No more!

As with any circuit of this type, the RF stages, and the frequency-determining part of the circuit especially, should be built with short leads, and stiff wiring. Top quality components will help.  The two 330pF capacitors in the feedback circuit of the 2N3904 oscillator stage should be NPO’s (or C0G’s – same thing), as should the 39pF capacitor. The coils were wound on toroids, and the coil assemblies mounted in octal tube bases. I spent a great deal of time on W8DIZ’ site, using his online calculators to figure out the number of turns required for varying degrees of coverage. Unless you build a receiver with the same variable capacitors, and use a very similar physical layout, you’ll need to do your own calculations, and then be prepared to tweak the final values of inductance and capacitance to get the coverage you want. Incidentally, I used a Hammarlund MCD-35-MX dual gang component for the main tuning capacitor. It was this one that I got a deal on over a year ago. The official specs say that each section has a capacitance of 6 – 31pF, but I also had to make a rough estimate of the stray and circuit capacitance when calculating the required values of inductance and capacitance to cover each band. My fine tuning cap was a Hammarlund MC-20-S, and I had to include the capacitance of that in the calculations too. This is the online calculator on W8DIZ’s site for the T68-6 core. He has similar calculators for all the popular toroids. Very useful stuff.  Note – for some reason, the calculator doesn’t always estimate the correct length of wire that needs to be used. This is easy to work around. Just wind one turn around a toroid measure it’s length, multiply that by the number of turns, and add a few extra inches for good luck (and pigtails).

Here’s a view of the RF board as initially built, before adding the extra (pre-AF board) preamp stage –

Here are the details of the coils wound so far, including the temporary “experimental” coil for 24-29MHz. I didn’t get as far as installing a link winding for this coil, but the main coil was picking up plenty of signal from the proximity of pin 7 of the tube socket to the coil. I have been very pleasantly surprised at how sensitive and stable the set is at these higher frequencies. Soon after winding it, I copied SSB on the 12M and 10M amateur bands, as well as plenty of over-modulated and very loud local signals on 27MHz :-)  Unless you also use the same values of tuning and fine-tuning variable capacitors, and closely copy my layout, your values will be different, but here is the info on my coil set so far. After a little while spent looking at it, it should make sense. Once you get used to figuring out how to wind a coil for a specific set of frequencies, it’s fun.  I have 15 coils so far, with ideas for a few more. I have already filled up my cigar box coil box, and am getting ready to make a second coil box and wind a few more coils. One of the really enjoyable things about a regen with plug-in coils is making coils for new bands. Fun!

If you wind too many turns for the link winding, you may find that you have to turn the regeneration control nearly all the way clockwise in order to reach oscillation, or you may not be able to reach it at all, as the link winding loads down the oscillator. It is particularly easy to do this on the higher frequency bands. If this occurs, remove a turn or two from the link winding. In operation, it is easy to overload the detector (as it is with all regenerative receivers). I use my Sproutie with a large outdoor antenna and find that on the lower bands, I usually only need to operate the set with the RF “gain” control set halfway.

The 15855 – 17850khZ coil stops about 50KHz short of the top of the 16M band, which is nominally 17480 – 17900KHz. However, all these coverage figures are quoted with the fine tuning control set to maximum capacitance. With the fine tuning control, I can tune all the way up to 17900KHz with that coil plugged in.

With the first set of coils I wound for specific bands, I was using significant values of padding capacitance across L1 in order to reduce the frequency swing caused by adjustment of the main tuning capacitor. I noticed after a while that the specific band coils weren’t giving such good sensitivity as the general coverage coils. I have since discovered that it is best to avoid large values of parallel fixed capacitance, as this reduces the Q of the tank circuit at resonance. Adding a capacitor of a few pF to tweak the coverage is fine, but large values (of the order of 50 or 100pF) will reduce performance. If you want to reduce the frequency swing to cover a narrow band, best to achieve it with the use of a capacitor in series with the main tuning capacitor instead. The Q of the tank at resonance seems to be maximized by using as much inductance and as little capacitance as possible. This is more noticeable on the higher frequency bands.

The table for specific band coils is a work in progress. I will add to it as I wind more coils –

The coils were constructed in two different ways. The lower frequencies used a larger T68-6 core which I mounted with nylon hardware. I first took a #10 nylon bolt, cut the head off, and epoxied it into the hollow center spigot of the tube base thus –

Before adding the toroid, any jumpers and capacitors were soldered in place (this is going to be the 3050- 3950KHz coil). The soldering’s a bit messy, but it was the first time I had soldered one of these things –

A couple of nylon nuts followed, then a nylon washer, and then the toroid, topped off by another washer and finally, another nut –

The higher frequency coils used T50-7 toroids, and were mounted vertically and secured with a couple of dollops of hot glue from a glue gun. In the following picture, the 3050 – 3950KHxz coil is on the left, the 14460 – 15980KHz coil in the middle (in a white ceramic tube base), and the 8040 – 10720KHz coil on the right.  The middle and right coil were pictured before the hot glue was added –

Here’s the 14460 – 15980KHz coil with the 2 dollops of hot glue to secure the toroid. I like these ceramic bases and think I’ll use them for all subsequent coils –

The coils for the higher frequency bands need less in the way of a link winding, such as 1/2 a turn, which is simply a piece of wire passing through the toroid, but not even being wound around it. For the 16M/17M coil, I found that a 1/2 turn from pin 1 to pin 7 wouldn’t allow the circuit to oscillate, so I used a simple u-shaped loop of wire between pins 1 and 7 placed near the toroid, as in the photo below. The link winding is the green wire. My attempt at using a 1/2 turn link winding for this coil involved a wire from pin 7 through the toroid to pin 1, and this stopped oscillation. However, it’s possible that a 1/2 turn from pin 7 directly through the toroid to pin 4, which is also at ground potential. might allow oscillation while coupling more signal into the detector (it’s a shorter run of wire). I didn’t try it though, opting instead to go for a loop outside of the toroid. Experimentation is definitely key here, and it’s one of the things I had in mind when building The Sproutie. Once you’ve built the receiver, you can still have plenty of fun designing coils for many different bands and amounts of coverage. Here’s that 16M/17M coil, showing the green link winding –

The coil for the 16M BC and 17M ham bands. This one covers 17400 – 18200KHz.

When designing coils for The Sproutie, here are a few things to bear in mind –

Adding padding capacitor(s) across the coil will bring the overall frequency down, and limit the range of frequencies that the main tuning capacitor will cover (as the tuning capacitor is now just part of the overall capacitance across the coil). However, if you place too much capacitance across the coil, the circuit will not oscillate. When making estimates and performing calculations, remember to include the capacitance introduced by the circuit, and stray capacitances. Another strategy for limiting the range of frequencies the tuning capacitor covers is to put a capacitor in series with it (the tuning capacitor).  If I haven’t already mentioned it, the online calculators on W8DIZ’s site are great for figuring out resonant frequencies for tuned circuits involving toroids. The calculator for the T50-7 is here, and the menu to the left of the page has links for the pages for each of the other toroid cores. Each page also tells you what range of frequencies that particular material is good for. However, even after you think you’ve figured out what values you need for the inductor and capacitors, whether you’re going to use padders, series caps etc, you’ll most likely still have to do some tweaking of values until you get the coverage for each coil that you want, based on observation and experimentation. Once you’ve got the exact values you want, make sure to hot-glue the toroid to the tube base. If you don’t do that, you’ll experience instability and microphony. It’s amazing what difference a couple of dollops of hot glue will make!

For the chassis, I first looked at what was available in off-the-shelf sizes and couldn’t find anything that fitted the bill. Hammond have a good selection of different sizes, but their enclosures, for the most part, use 0.04″ thick aluminum. I wanted something thicker, for a very sturdy structure, so I decided to look into having a custom chassis made. A bit of searching turned up two businesses that manufacture aluminum chassis’ for homebrew tube amp enthusiasts – Dirty Dawg Amps, a US based business who are temporarily out of business due to a fire, and Seaside Chassis Design, who are located in Novia Scotia. Seaside Chassis use a minimum of 14 gauge aluminum for their enclosures. 14 gauge is about 0.064″, which I knew would make for a nice stout case.

Terry was very communicative and straightforward via e-mail about what he could do and what it would cost. I sent him rough drawings, with dimensions, of the chassis, front panel, and mounting bracket for the main variable capacitor that I was hoping he would be able to fabricate. He was able to make all 3 items and on top of that, he would punch all the main holes for me, leaving me just to drill the smaller holes for mounting screws. This was great news, knowing that I would shortly have a solid and well-made chassis on which to build this receiver.

I dropped the ball somewhat and didn’t take a picture of the chassis when it arrived, but here’s what it looked like with all the main components fitted, before wiring it all up. The 2 biggest factors in making this receiver look so grand are the National “N” dial with Velvet Vernier drive, and the excellent chassis. Does this look inspiring or what?

The controls on the upper row are, from left to right – regeneration, the main tuning knob, and the fine tuning. On the lower row, also from left to right is the headphone socket, RF attenuation, the bass boost switch (down = more bass) , the low-pass filter cut-off control, and the AF gain control.

Here’s a view from the back at this point in the construction. Look at that accurately made chassis, front panel, and capacitor mounting bracket. Terry from Seaside Chassis Design did a great job –

Both the RF board (without the extra AF preamp that was built later) and the AF boards installed but not yet wired up. All cables are tagged for easy identification –

Another view of the underside, before everything has been wired up –

The next task was to begin wiring the boards to each other and to the controls. Looking at this view of the underside, I’m thinking that I perhaps could have put a little more effort into dressing the cables more neatly, but it’s perfectly functional. The schematic shows pin 1 of the octal base being grounded but as I was wiring it up, I decided to also ground pin 4 –

Some more views of the underside from different angles and distances. I only twisted the 12V supply lines together for neatness and not for any electrical reason, though it does rather make them look like tube filament wiring :-)  Just to the left of the antenna socket on the right, is the phono jack for the line out. This is such a useful feature. In fact, as I write this, I am using the line out to record KCBS from Pyongyang on 11680KHz. On the other side from the BNC antenna connector, you can see the DC power jack with the reverse polarity protection diode and the RF bypass capacitors. Vinyl grommets were used for all wiring that needed to pass through the chassis. RG-174/U in the form of Belden 8216 was used for the connection from the BNC antenna connector to the board, and lavalier mic cable with 2 conductors and a shield for all other connections to controls (and to the phono jack) –

A view from the top, with a coil plugged into the octal tube base. The shaft couplers came from different sources. The one on the left, on the main tuning control, is a Jackson Bros part, purchased from Mainline Electronics in the UK through eBay. The coupler on the right was made from all aluminum by John Farnsworth KW2N. He has a small business making these and can also make custom sizes, if you have a non-standard shaft you want to use. For instance he just made a 3/16″ to 1/4″ coupler for my next project. John sells on eBay, but you can also contact him directly through his fledgling website (not yet finished) here. I really like his all-aluminum couplers –

The original intent was to mount the internal speaker on top of the chassis on the side using some kind of simple right angle bracket(s). I didn’t ask Terry from Seaside Chassis to fabricate a bracket for me because at that point, I didn’t know what speaker I was going to use. Looking around my room for something I could use, I noticed an unused LMB Heeger enclosure #143 in the size 4″ x 4″ x 2″ – exactly the same enclosure I used for the 31M version of the WBR. I figured that the top part of the box, being a U-shape, could be used as a bracket. If using that part though, why not use the whole box? There might even be some extra acoustic benefits to housing the speaker in a little case, and having it fully enclosed will protect it from dust and small bits of wire, metal filings etc being attracted to the speaker magnet (which happens here in the shack). The sound was a little “boomy” with the case closed, so I stuffed some foam in with the speaker, and it cleaned the “boominess” right up. Although you can’t really see it in these next shots, the speaker case is bolted to, and spaced off the chassis with 4 vinyl grommets to dampen any unwanted acoustic resonances in the chassis. The speaker wire enters the speaker enclosure through a grommet in the side. It’s a small detail, but the grommet is mounted not in a hole, but in a slot in the side of the cover. That way, when I remove the cover of the speaker enclosure, I can slide the grommet out, leaving the grommet still on the speaker wire, and allowing me to completely remove the cover –

There are a few improvements and modifications I’m considering making to The Sproutie but it is now completely functional, and this is how it looks at this point. I must say that I think it’s looking pretty good –

I was lucky enough to obtain a National “N” Dial in good condition and nice working order – not all of them look or operate this well. I bought several from Gary at Play Things Of Past and used the nicest one. The tuning knob and reduction drive are an important part of the feel of any receiver, and can do a lot to affect the operating experience so I’ll say a few words on that subject if I may. Before, I do, here’s a clip from a page of the 1947 National Radio catalog. I get a kick from seeing vintage parts in old catalogs, then seeing the exact same thing, in really nice condition, in front of me. It’s a bit like meeting a celebrity for the first time :-)

I was initially concerned that the 5:1 reduction ratio of the National drive wasn’t going to be high enough for accurate tuning on the HF bands – it was a good part of the reason why I chose the value of the main tuning capacitor and wound the coils so as to limit the tuning ranges to around 2MHz or less. This approach results in more coils, but really helps in creating a regen that can be set to a particular frequency, and from which you can read the frequency (with the help of a calibration graph – more on that later.) This receiver can be set to within a few KHz of any frequency. This is good enough for finding a particular SW AM broadcast station. I can also read the dial setting and then consult my custom calibration graph to find what frequency I am on to within a few KHz. It’s not much by modern standards, but is pretty good for a regen with an analog dial.

The National “N” Dial is marked from 0 to 100 and thanks to the vernier scale located at the top, it can be read to one-tenth of a point. These dials, when in good condition, have a firm yet smooth action with no backlash that makes tuning a receiver like this a good experience. Another thing to note is that these dials were manufactured with CW (clockwise) and CCW (counter-clockwise) characteristics, meaning that as you rotate the dial clockwise, the numbers either go up (CW type) or down (CCW type). This makes sense when you consider that variable capacitors were made as units that either increased in capacity as you rotated the spindle clockwise, meaning that the frequency went down (CCW type), or as units that decreased in capacity as the spindle was rotated clockwise, meaning that the frequency went up (CW type). The latter type is the convention for variable capacitors today. When we rotate our tuning knobs clockwise, we expect the frequency to increase. Back in the days when our predecessors thought more in terms of wavelength, they would have expected wavelength (instead of frequency) to go up with a clockwise rotation of the knob. This particular regen uses a CCW-type variable capacitor, so I married it up with a CCW-type vernier dial. It does take a while to get used to the fact that the frequency goes down when you turn the tuning knob clockwise, but I am beginning to adjust. There seem to be quite a lot of these lovely old National “N” dials around, if you take the time to look. A fellow homebrewer told me that his local electronics surplus store had a number of them in good condition for a very good price (I believe he bought them all!) Hamfests and swapmeets are also a good place to look. eBay is another possibility but the prices asked are a bit on the high side, in my opinion. I got mine from Gary at Play Things Of Past. He was easy to deal with.

Note – the National N dials have 3 small rubber/fiber bumpers installed on the mounting plate to prevent the front metal “flange” (the part with the engraved dial markings) scraping on it when the dial is turned.  If your dial is in good condition, none of the main parts are bent, and everything is running “true”, you can remove these bumpers. I did, and the result was a dial that rotated very smoothly. With the bumpers in place, there is a very slight scraping sound as the dial is turned. If you do this, make sure to save the bumpers in case you later wish to re-install them.

One downside to each coil only covering a relatively small part of the shortwave spectrum is that you end up with quite a few of them – more if you decide to wind specialty coils for specific bands. A coil box was definitely in order, so I headed to my local cigar and tobacco shop and purchased an empty cigar box. A trip to the local craft store yielded a length of bass wood, which is a little harder than balsa but can still be cut with a sharp craft knife. I cut slots in the lengths of basswood so they would slot together to form dividers to store the coils in –

The dividers installed in the cigar box, with the coils that had been wound so far (at time of writing this, I now have one more, for the 120M BC band) –

In order to know where you are on the band, you’ll need to calibrate your dial.  I accomplished this by plotting a graph for each coil with frequency on the x axis and dial markings from 0 to 100 on the y axis. For frequency references, you can use a crystal-controlled marker, or off-air signals and an online frequency database such as short-wave.info  Bear in mind that the setting of the regeneration control does alter the received frequency. Probably the best way to standardize your results is to keep the regeneration at or just below the point of oscillation at each dial setting that you take a measurement. The following is one of the graphs I am currently plotting. The original was larger and it is a little hard to read the markings on each axis on this smaller version. That’s fine, as your calibration will be different anyway.  In this graph, look at the line formed by the red dots (the black dots are something different – you can ignore them) –

The variable capacitor I used is what Hammarlund called a “midline” type in which the moving plates (the rotor) were mounted off-center so that the relationship between degrees of rotation and the resulting capacitance was non-linear.  The intent was to keep the relationship between degrees of rotation and frequency fairly linear and by looking at the graph, you can see that it is not bad at all. I also found that once a graph was plotted, I was able to set the dial and return to a particular frequency with a good degree of accuracy and repeatability. When listening to AM stations with this receiver and it’s bandwidth, which is of the order of 10KHz, you can be assured of returning to a dial setting and hearing the station you want.

The Sproutie does work on SSB and CW, but SSB reception is trickier due to the need to control the signal input level (with the RF attenuation/gain pot) in order to prevent overloading of the regen detector and pulling of the oscillator, and to adjust the level of regeneration in order to inject the right amount of carrier. If the signal level to the regen stage is too high, the oscillator will pull, resulting in the signal sounding “wobbly” due to FM’ing of the oscillator. This happens very easily, even with moderately strong signals. My preferred method of operating the set when listening to SSB stations is to run the AF gain at, or close to, maximum volume, and to keep the RF “gain” low. Sometimes, I need to keep the RF gain twisted almost to zero in order to achieve a nice stable demodulated signal. When adjusted properly, SSB sounds good on The Sproutie, but it takes a fair bit more work than with a superhet fitted with a product detector. Hams and shortwave listeners who have used older superhets that used BFO injection into a receiver with a diode detector will be familiar with the technique of keeping the AF gain up high, and using the RF gain to control the signal-to-carrier injection ratio. In this case, we are also using the RF gain to prevent the detector from being overloaded and pulling the oscillator. Sound tricky? If you’ve never done it before, it can take time to get used to, but after a while, it becomes almost second nature.

While I’m on the subject of fine tuning, allow me to expound a little more on reduction drives. In contrast to the friction drive on the National “N” Dial I used for the main tuning, the reduction drive on my fine tuning is a Jackson Bros 10:1 ball drive which has a small amount of backlash and feels a bit “spongy”. I don’t like it, and am grateful that for my main intended use of listening to AM stations, I won’t need it. I may change this ball drive for either another friction drive, or a different ball drive.  The Xtal Set Society sell 6:1 ball drives manufactured (I believe) by Oren Elliot) that have a more pleasing feel. EDIT – I have since found that making the 2 screws that hold this mini ball-drive to the front panel very, very tight seems to eliminate the backlash and reduce the spongy feel a bit.  I suppose it increases the pressure on the bearings a little. For the time being, I’ll keep this drive but if I ever change the front panel, that will be the point at which I’ll drill a bigger hole for a more conventionally-sized reduction drive.

For the above reasons, if I were intending to listen to more SSB and CW on this receiver, I would definitely wind coils to spread each entire amateur band over the whole rotation of the dial, and make sure I had a reduction drive for the fine tuning with very little or zero backlash and a better feel (though having said that, the regeneration control works very effectively for fine tuning).

Another thing that has often interested me is the bandwidth of regens. In general, as you approach the point of oscillation, the bandwidth becomes narrower, until it is at it’s narrowest somewhere around that critical point. As you continue to advance the regeneration, the bandwidth broadens out somewhat. I connected the output of a simple noise generator to the antenna socket of The Sproutie, and took screenshots while running Spectrogram, which was being driven from the line out jack of the receiver.  All 3 of these screengrabs were taken just marginally below the point of oscillation (the ideal point for receiving AM). The first one was with the low-pass filter adjusted for maximum bandwidth –

Well, it’s obviously not the kind of brick wall shape we might expect from a good crystal or mechanical filter but if you look closely, the passband is about 25dB down at the 5KHz point and 30dB down at the 10KHz point, That’s not too bad for AM reception, though if you wanted to get really serious about it, a passband of around 5 – 6KHz with a much steeper wall would, of course, be more ideal.

Here’s a grab taken with the low-pass filter pot at the median point, which is looking better –

…and better still with the low-pass filter set to the lowest cut-off point –

It is important to remember that these spectrums represent the response of the entire receiver, and not just that of the front end. SSB and CW signals become higher-pitched as you tune away from the center of the signal, but although the audio frequency make-up of an AM signal tuned off-center does change, the whole signal does not become higher-pitched. Therefore, an audio filter will be more effective at rejecting off-frequency signals for SSB and CW signals than for AM. Nevertheless, the adjustable low-pass filter is very good at cutting down much of the high pitched static that can make simple receivers like this quite tiring to listen to for long periods whatever mode is being received. It makes The Sproutie feel like a “grown-up” receiver!

Here’s The Sproutie, with it’s coil box. I would have felt as if I had died and gone to heaven if I’d had this receiver as a teenager. I’m feeling pretty good about it at my current age of 50 :-)

The Sproutie is not completely finished yet (is any homebrew project ever truly finished?) The changes and additions I am considering include –

-Designing a thicker, and custom front panel with Front Panel Express, and making it a little wider than the current one to allow for a pair of instrument handles to be mounted

-Changing the 10:1 Jackson Bros reduction ball drive on the fine tuning control for something with less backlash and a firmer, less “spongy” feel

-Winding more coils for specific bands, so that the bands I am most interested in can be spread out over the entire dial, making tuning using just the main tuning control even easier

-I had also considered finding a local cabinetmaker to make a wooden cabinet for The Sproutie, but am not too sure about the convenience of sliding the chassis out of the cabinet every time I want to change a coil. If you’re thinking about building a receiver like this, completely enclosing it in metal would be quite a good idea – perhaps with a hinged flap or door on top for coil-changing. Regenerative receivers are quite sensitive, and this one picks up signals from my computer and/or my monitor, which are located nearby

It always feels good to build something that works, and The Sproutie certainly does that. It’s a great little receiver for shortwave listening and with an extra tube base, a toroid, some wire and a few extra capacitors, you can add whatever frequency coverage to it you like as you go along.

Oh – and I just realized I didn’t explain that Sproutie is the nickname I gave my 2 1/2 year-old cat Sprout, whose ham radio name is Sprat The QRP Cat. I had already named one of my home-brew radios after a kitty I used to have called Rug, so figured it was time to honor Sproutie in the same way.

Sprat The QRP Cat aka Sprout aka Sproutie, after whom this receiver is named.

Videos of The Sproutie in action are here.

Thoughts on using The Sproutie to receive SSB are here.

Sproutie is ever-curious, just like her regen namesake is always seeking out signals.

I continue to update and re-write this post, as I make additions and improvements to The Sproutie. I would rather incorporate them here, rather than into subsequent, and separate posts. That way, if you are thinking of making your own version of this receiver, you can get all the latest updated information by reading this one (rather long!) post, instead of checking my entire blog for updates. As of February 2015, I have filled the entire cigar box with coils, with one to spare (that one is plugged into the receiver). The latest coil I made was for 17400-18200KHz to cover both the 16M BC band and the 17M ham band. 16M is just about the highest frequency shortwave BC band that is in regular use so I now have all the SWBC bands covered – most of them with coils specific for the individual bands. Here’s what my coil box looks like now. The unmarked coil sitting at the top of the box is the experimental one for 24-29MHz –

This cigar box cost $5 from a local tobacconist and makes an excellent coil box. The unmarked ceramic tube base sitting on top is the experimental coil for 24-29MHz. 4 adhesive vinyl bumpers stuck to the bottom help to protect it from rough surfaces.

August 18, 2014

The HumanaLight – A Flashlight That Uses Your “Dead” AA Batteries

A couple of weeks ago, I was spending a very pleasant hour or so waiting in the front yard for the mail carrier to deliver some packages of vintage radio parts I had ordered a few days earlier. My neighbor’s cat Stephen was lounging around with me, and it was one of those perfect afternoons where time almost stands still. It was warm, with a slight breeze and as Stephen and I lay on the garden path looking up at the sky, I nearly forgot the reason for my being out there in the first place.

Eventually, the mail carrier arrived and Stephen took off. He’s an indoor/outdoor kitty, so mistrust of humans he doesn’t know is a valuable trait. The mailman handed me two packages packed with vintage dials and other parts – and another, smaller packet from my friend Thomas Witherspoon K4SWL. Inside was a kit to build the HumanaLight – a flashlight that uses the residual energy in depleted AA batteries to provide useful light for much longer than would be possible without this neat circuit –

The HumanaLight is based on the “Joule Thief”, a self-oscillating voltage booster that boosts the low voltage from a nearly depleted AA battery in order to light an LED. It does this, of course, at the expense of a greater current draw from the battery but it’s not as if this energy was going to be used otherwise.

Thomas is the founder and director of Ears To Our World, a non-profit organization whose main goal is to empower people living in extreme poverty or war-torn areas of the world by distributing self-powered short-wave receivers to them. It may sound like a simple thing, but for people living under very difficult circumstances, access to reliable news and information from areas directly outside their own can be a lifeline.  This page explains it more succinctly.  Many of the radios that ETOW distributes incorporate LED flashlights, and it was noticed that this feature of the radios is very popular. If you don’t have reliable electrical service, a flashlight that can be powered by hand-crank or batteries charged by solar cells is a very useful thing to have.

The HumanaLight was inspired by the LED lights on the self-powered radios distributed by ETOW. It’s a neat idea – a little LED light that is powered by a novel power source – the residual energy in nearly-depleted AA batteries. When the voltage in the AA cells you are using to power your portable radio, camera, or other device, has dropped so low they will no longer power it, there will most likely still be enough energy  in them to run this little flashlight for a useful length of time.

The HumanaLight comes with an easy to follow set of step by step instructions for assembly. It would be an ideal kit for a beginner –

Stephen strolled along to see what was going on and decided to inspect. Luckily, it passed the whole process without a scratch –

Taking a brief break from the rigorous quality control process –

Assembly is simple – just a few components to solder into the board and bingo – you’re done!  The kit comes with two white LED’s – a standard size one, and a jumbo one. You also have the choice of mounting the LED either with the leads bent at right-angles so that the LED points forward like a flashlight, or you can solder it flush with the board so that it points upward. I couldn’t decide, so I didn’t solder it in at all for these pictures, just placing the LED through the mounting holes without soldering (I later decided on using the jumbo LED and soldering it in flashlight-style).

For comparison, I first plugged in a fully charged NiMH cell with an unloaded voltage of 1.35V. You can’t really get an idea of relative brightness from these photographs, as the LED completely blows out the highlights but here’s the picture anyway –

I then tried an old battery that measured 0.76V unloaded –

You can’t see it too well in the picture, but the “dead” battery gave noticeably less intensity. However, if I was in such a situation that I needed an emergency light, and all I had were a few nearly exhausted batteries, I’d be glad for this much light to see my way around. I had another cell in a similar state of depletion, but no others to try. I have read comments from others who tried AA batteries with unloaded voltages of ~0.4V that didn’t work. This circuit does usefully boost the voltage available from a near-depleted cell but it obviously has limits. A cell with an unloaded voltage of ~0.7V isn’t useful for much though, so it’s great that you can use the HumanaLight to get some useful emergency light from it.

The board has a handy hole at the opposite end from the LED – no doubt for a lanyard or suchlike. You could also use it to hang the HumanaLight on a nail on the wall for easy access during an emergency. It would be fun coming up with an enclosure for this – perhaps some thin-walled tubing. I have left mine as is. I plugged a freshly-charged cell into it and switched it on Friday night. Although not an intense beam (it is, after all, a single LED) it raised the ambient light level in my room enough to make it a bit harder to get to sleep, so the next morning I moved it into the hallway where it remains. I’m keen to know how long it lasts.

The HumanaLight is available from Universal Radio here. With circuit design by Gregorgy Majewski and board layout by David Cripe NM0S.  It’s a neat kit and if, like me, you believe that shortwave radio is still a very relevant and useful way to get news and information to people living under very difficult circumstances, purchasing it is a great way to contribute to the cause.

 

 

August 6, 2014

N8RVE’s WBR Regen Receiver

Filed under: Uncategorized — AA7EE @ 10:54 pm
Tags: ,

I’ve been chatting with John N8RVE via e-mail for a while now. He built a little receiver that I dubbed “The Rugster” - it’s a direct conversion receiver consisting of a standard NE602 front end, with a “poor man’s varactor” (1N4001) to tune the bottom 50KHz of 40M. The AF stages and narrow filtering are provided by the 4SQRP Hi-Per-Mite filter.  John’s Rugster initially drifted a little, then when he used NPO caps in the frequency sensitive  parts of the circuit, the drift issue cleared right up (funny how that happens!)  He was very happy with his Rugster, as am I with mine.  It’s always great to hear of fellow homebuilders successfully completing projects.

More recently, John built a WBR regen receiver with a FAR Circuits board that he picked up at Dayton, and sent along some pictures of the final receiver. Talk about a neat and original enclosure – he used a piece of plexiglass and a reticle from an oscilloscope –

That’s a neatly wound toroid John –

John says that it sounds great, though he uses an outboard amp, as the audio level was low.  I’m thinking it shouldn’t be too hard to construct a one-transistor pre-amp ugly-style, so that this receiver can pack a little more audio output.

Great job John, and thank you for sharing your success with us!

« Previous PageNext Page »

The Rubric Theme. Create a free website or blog at WordPress.com.

Follow

Get every new post delivered to your Inbox.

Join 1,353 other followers