Dave Richards AA7EE

May 24, 2013

Taking Stock, New Desert Ratt 2 Recording, and A New Tut80 Run

When I started this blog almost 4 years ago, I was getting a (very small) handful of page views every day and had no idea that anyone would find it at all interesting or useful. In fact, I don’t think anyone did at first. Then I started building a few things and found that some people enjoyed looking at the pictures of my builds and in some cases, were encouraged to try building things themselves.

I used to think that in order to have a blog, website, or other kind of internet presence, you needed to be really, really good at something or it wasn’t worth putting your stuff out there, but I was missing the point. I think that the point is sharing. I don’t need to be one of the best at something, because everyone does things differently. If I do my best at something, and share the way that I did it, that information could well be useful to someone else who was trying to figure out how to do the same thing. Maybe my approach will present an interesting alternative to someone who was thinking of a different approach.

My last post on the NA5N Desert Ratt 2 Regen is quite a good example of this. I certainly didn’t design it so wasn’t offering anything radically new, but for anyone wanting to build one, there aren’t very many examples on the internet, with pictures, of DR2’s. Of the ones that exist, there aren’t a lot of detailed pictures, with discussion of construction details, all in one place. Perhaps someone was interested in building it, but was wanting to know the winding information for toroids (which doesn’t seem to be available online), or was wondering whether the tuning would be too fine, what kind of reduction drive to use etc. This is why I like to include this kind of information in my posts, in case it can help someone.

Since I sold my FT-817 2 years ago with a desire to rely more on homebrew gear, things have gone quite well. Admittedly the main rig at AA7EE has been a K2, which is not exactly home-brew, but it still felt good to prove to myself that I could assemble a kit of such complexity.

Apologies for the following 2 lackluster photos (it has to do with my inability in using flash to light indoor scenes, among other things) but here are the main bits of gear I have built in the last 2 or 3 years. These are the ones that worked; I left out the partially completed projects (which includes 2 DSB rigs that have working receivers but not fully working transmitters) .

On the top shelf, from left to right, is the 40M DC receiver using a Hi-Per-Mite filter, and an OHR WM-2 QRP Wattmer.

On the middle level is my K2, Fort Tuthill 80 (see news about a further release of Tut80 kits below), and the NA5N Desert Ratt 2 Regen.

On the bottom level you can see the Norcal 2N2/40, the first beta of the CC-20 and the first beta of the CC1 (it’s successor), both sitting on top of the G3WPO DSB80, and the N1BYT WBR Regen Receiver for 40M.

On the desk in front of that lot is a little 2 transistor TX on 7030 based on the Pixie 2 design. I have used it successfully with the WBR for a 100% home-brew on-air experience! –

The reason I arranged all these projects at my operating position and took their picture together is because I wanted to review my progress so far.  My interests are shifting, and it looks like ham radio will be taking a backseat to other pursuits for the next few months. This was a good way of putting a bookend on this period before I begin another one. This color shot shows why I usually drag my projects into outside light in order to photograph them.  I really need to work on my flash lighting skills (note the blown-out red channel on the freq displays – a bit of HDR work with Photoshop could have helped this, but sometimes I just want get on with things and post them!)

In other news, the videos I posted of the Desert Ratt 2 were intended to give a general sense of what this neat little regen is like to tune around the bands.  It doesn’t really give a good sense of what the audio from the receiver sounds like though, as I was using an MFJ-281 ClearTone speaker, which has a restricted audio response. On top of that, I was using the internal microphone of an old compact camera (Canon A80) to record it. To remedy this I made a recording the other night from the speaker jack of the DR2 directly into the line input of a little flash recorder (the Marantz PMD620, if you’re interested) and posted it to Soundcloud.  This will give you a much better idea of the quality of the audio from this receiver. Unfortunately, band conditions weren’t too good, so I wasn’t able to find any consistently strong signals with little in the way of QSB, but this recording of Radio Habana, Cuba isn’t too shabby.  It has been edited down, and the edit points are marked by cowbell sounds. When the signal gets strong, you can hear the wide frequency response and good fidelity of the Desert Ratt 2 –

And finally, I’ve had the pleasure of an e-mail chat with John K5JS, of the Arizona ScQRPions, and he informs me that they will be producing a final run of the Dan Tayloe designed Fort Tuthill 80 Direct Conversion CW QRP TX/RX. They already have the boards and many of the parts, so it sounds as if they just need to order some more parts and have a kitting party. This is no mean feat, as kitting is an awful lot of work. I don’t know when this will be happening, but it is definitely in the works. As you no doubt know, QRP Kits are selling versions of this rig for 15M and 160M, but I think it would be fun to buy another of the Tut80 kits when they come out and mod it for 40M. Has anyone done this? Could they post details of their mods to the Tut80 Yahoo Group if they have, perhaps?

In the meantime, the weather has been getting nicer and combined with the fact that the bands haven’t been in great shape, it’s as if mother nature is coaxing me to get out more. I plan to do just that. My bicycle has a new chain, and the weather is perfect for bike rides.  There’s also a new camera calling my name, which will require new photo software, and the inevitable upgrade of my operating system (I’m still on XP), as well as much time spent outside taking lots of pictures. I’ve been looking at my rather old photo portfolio and realizing that there is much work to be done, and much fun to be had.

Much work. Much fun,  I love it when the two go together 🙂


October 16, 2011

QRP Adventures With T32C – and A Tut80 into a 40M Dipole

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 4:15 pm
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The main reason for this post is to share my surprise and joy at the fact that the night before last (Friday night) I worked T32C with my Tut80 – a QRP rig designed by Dan Tayloe N7VE that has a direct conversion receiver and a CW transmitter that in my particular case, puts out 4 watts (they seem to vary.) It’s not the kind of rig I’d normally think of using to contact a DXpedition, but as I don’t currently own a more conventional rig with dual VFO’s, I wasn’t about to miss out on the T32C fun by not trying at all.  What made the contact with T32C even more surprising to me was not only that I was only putting out 4 watts, but that I was putting it out into an inverted vee dipoole cut for 40M with the apex at 47 feet, and fed with coax!  If I were using QRO,  I don’t think I’d attempt to tune up such an antenna on 80M and certainly wouldn’t expect it to perform all that well. However, with only 4 watts output, I didn’t think much ill harm could come from excessive feedline radiation and so I tweaked the knobs on the ATU and hoped for the best.

Let me start from the beginning though. On seeing all the fun many people have been having working T32C, I wanted to at least work them on one band. The only rigs I currently own are the Norcal 2N2/40, the Tut80, and the beta version of the NT7S-designed CC-20. They are all QRP monoband rigs, none of them have dual VFo’s, and so the only way to work split frequency is to use RIT and hope that the split isn’t more than about 1.5 – 2KHz. I tried to snag them a few times on 40 without much success, but that was fairly early on when there was plenty of competition from other US stations. Then last Saturday morning during the Oceania DX Contest, I noticed that T32C had entered the contest and were working simplex on 40.   It was 5am, there wasn’t a whole lot of competition, and I got them  in the first few tries with 4 watts from the Norcal 2N2/40 to my only HF antenna – an inverted vee cut for 40 up at 47 feet. Bingo! Later that day, I saw myself in their log and that was when lightbulbs started coming on and ideas forming. How many bands could I work T32C on with my modest collection of QRP rigs?

I wasn’t able to put the CC-20 into service just yet, as I had just fried one (or more) of the active devices during beta-testing and was awaiting parts in the mail from Jason NT7S. That left the Tut80. The idea of working Kiritimati on 80M was very appealing, but I have never had much success on that band due mainly to my inability to erect effective antennas at the various places I have lived.  All I had to work T32C was a QRP direct conversion transceiver on 80M and a 40M coax-fed inverted vee. What do you think my chances were? I didn’t think they were very high, but all I had to lose was time, so I had a go.

VOACAP online comes to us courtesy of Voice Of America. It’s a great tool for  estimating coverage areas, and best times and frequencies for establishing contacts on the HF bands.  Apparently, it’s not too effective on the lower frequency bands, but this is what I came up with for a station running 5 watts of CW to a dipole at 50 feet, which was pretty close to my situation.  For the receiving station, I entered either a 1/4 wave vertical or dipole at 50 feet (can’t remember which.) They were actually using a Beverage. This graph predicts the chance of establishing contact between my QTH and Kiritimati during the month of October 2011:

From the above, it looked like my best opportunity on 80 would be from 0600-0800 utc. That morning, the T32C team had posted on their website that in response to requests for more 80M CW activity, they would be QRV on 80M CW for 2 days in a row at European sunrise, then on SSB for 1 day, then CW for 2 days, and so on.  This schedule coincided with my best chance to contact them as predicted by VOACAP – excellent!

I haven’t worked that many DXpeditions in the past, but on the few occasions I have,  I’ve done it manually with a key or paddle. It wasn’t until I saw AE5X’s video of him working T32C with his K3 that I realized for QSO’s like this, you can enter your overs into the keyer memory, then when it’s your turn to send, all you have to do is push a button. Thanks for that John. Incidentally, John contacted them on CW on all HF bands (including top band) , of which the 40 and 80M QSO’s were QRP. His 40M QSO was with just 2 watts.

I duly entered the following into one keyer memory:


and this into a second memory:

RR 599 TU dit-dit

On reflection, the dit-dit was unnecessary.

I got the Tut80 set up and started watching the HRD DX Cluster Site for the appearance of T32C on CW.  At some point during the evening (my time) they arrived, and were listening 1KHz up from their frequency of 3516 KHz (very do-able by the Tut80’s RIT – thank goodness it wasn’t a much bigger split).  Although other stations on the west coast were hearing them with quite strong sigs,  they were fighting with the high noise level for me. I think the main reason for that was my poor antenna for 80M (the 40M inverted vee fed with coax) which was picking up a lot of QRN but not a lot of the wanted signal. The other reason was probably that although the Tut80 is a good receiver as far as fairly simple direct conversion receivers go (stable VFO, no common mode hum or broadcast breakthrough and 700Hz-wide audio filter with nice sounding roll-off), it’s not exactly a contest-grade receiver. I could really have used a good 80M antenna and a single-signal receiver with some nice sharp crystal filtering, but the Tut80 and my compromise antenna was all I had, so it was what I used.

My preference is for a 500Hz sidetone, and the 1KHz split worked out very nicely because by tuning the direct conversion receiver in the Tut80 to 3516.5 KHz, I could hear both T32C on 3516 and the stations that was calling on 3517 – both at a 500Hz pitch. Double-signal reception is not usually thought of as offering any particular advantages, but this was one nice “extra”. If I wanted to listen just to T32C, all I had to do was twist the RIT knob and tune to 3515.5 KHz – 500 Hz below the T32C transmission frequency.  Neat eh?

Although they were only barely copyable to me, I could make out that they were calling EU EU – meaning they wanted calls from European stations only. This made sense, as part of their stated goal was to exploit all openings to Europe.  My hope was that by the time the grey-line had moved across Europe I’d still be able to copy them, and they’d open it up to non-EU stations.  I opened up a grey-line map at worldtime.com and started watching as sunlight slowly covered more and more of the continent.  QSB was taking T32C just above and just below the high noise level at my QTH, so I’m not sure exactly at what point it happened, but somewhere around the time that most of Europe was in daylight and the grey-line was over the UK, I realized that I was no longer hearing EU EU at the end of the CQ calls. Hoorah!  I called a few times, heard them work other stations (including a Brazilian station who had mentioned in the cluster that he was about to lose propagation and really wanted to work them). Then on around the 3rd try, I heard my callsign and a 599.

This was what the grey-line map looked like as T32C came back to my call.  The sun had set in Kiritimati about 2 1/2 hours earlier and they were in darkness at this time:

Huh? Really? Did I just hear my callsign coming back to me through the noise? I hurriedly hit the second memory button , and realized that the dit-dit I had programmed in straight after the TU was unnecessary, because by the time the dit-dit was over, they’d already started calling again.  I appeared in their online log less than 30 minutes later.

I was stunned. I’d worked them on 80M with this:

to a 40m inverted vee fed by 75 feet of coax! I think the coax must have been forming a pretty substantial part of the antenna as well as the dipole elements attached to it. It was all due to what is probably a low-noise location on Kiritimati, good antennas and world-class operators. My hat is off to the ops at T32C. They are doing a fine job.

Next on the agenda is to work them with the CC-20. They haven’t been on 20M CW in the last couple of days. I’m guessing it’s because the higher bands have been hopping. Hopefully for me, there will be a day or two with reduced propagation propagation on 17-10 so that the FB ops on Kiritimati will come down to 20M CW, and I can see whether the XIT that Jason NT7S just implemented in firmware is doing it’s job 🙂 20 could be a tough one though.  I suspect there will be a lot of strong signals to compete with.

It speaks to the dedication and experience of the T32C team that despite the fact the container carrying their equipment never made it to the island, they continued with the DXpedition and still managed to conduct a very well-run operation, albeit with 9 simultaneously operating stations instead of the originally-planned 15. These excellent operators, a very informative web-site, regularly-updated online log, and the fabulous HF conditions, have all combined to bring the excitement of working a DXpedition to hams like myself who, in the words of the Pet Shop Boys  “Wouldn’t Normally Do This Kind Of Thing”.

I know I’ll be following DXpedition news more carefully in the future and when I get the K2 that just won’t get itself out of my head, will lose the coax and feed my 40M dipole with balanced line.

I’m rather glad that I don’t currently have a more conventional HF multi-band rig.  If I did, I wouldn’t have pressed the Tut80 into service, and I wouldn’t have experienced the satisfaction that comes from being able to say “I worked the T32C DXpedition with the Tut80”!

February 28, 2010

The Tut 80 Complete

There are two Tuts in the San Francisco Bay Area that I know of – The King Tut Exhibition currently showing at The De Young Museum in San Francisco, and The Fort Tuthill 80 in my apartment in Oakland. It’s been a longish road gettting this little direct converison transceiver completed, mainly due to the fact that I originally housed it in a larger case with a vernier dial before deciding against it and rehousing it in a smaller case without the vernier.

As I’ve mentioned before, the Fort Tuthill 80 is an 80M direct conversion CW transceiver designed by Dan Tayloe N7VE, who has spent a lot of time thinking about distributed filtering in direct conversion receivers, and it shows in the performance of this little radio. If this the first time you’ve come across this radio, the Yahoo Group will give you a lot of info.  The AZ ScQRPions have the rights to produce the 80 meter version, and then Hendricks QRP Kits will be selling versions for other bands.

The first part of the build was covered in this post.  I wasn’t too sure about what I thought would be the tricky tuning that may result from coverage of something like 50KHz of band in just a half turn of the knob.  That was equivalent to 100KHz a turn, so my thoughts turned to fitting the rig with a reduction drive.  Dan advised me to try it without the vernier first, as he had used a vernier before, and felt it unnecessary. I was convinced that a vernier was the way to go though, and this was it looked like in the case before fitting the frequency readout:

I was pretty excited about the prospect of this with a digital frequency readout and yellow decals, but after a few days playing around with it, I decided that I didn’t like the vernier. Dan didn’t mention why he hadn’t been keen on the vernier, but my experience was that the advantage of the 8:1 reduction was negated by the stiff feel to the tuning – precisely tuning a signal wasn’t as easy as I was expecting.

Folk in the Yahoo Group had been talking about fabricating cases from PCB materials. There’s a really good tutorial on how to fabricate a case from PCB material written by Ken WA4MNT. You can find it in the files section of the Yahoo Group for the Tut 80. I’ve used this method for constructing VFO enclosures in the past, but never for a case to house a whole project. In retrospect, this really is the way to go; the rigidity I would have gained from using this type of enclosure would have helped the short-term frequency stability, though it’s pretty good with the case I ended up using.

Terry WA0ITP mentioned the Ten-Tec case TP-41 as a possible enclosure.  John AE5X used one for his Tut80, commenting that it was perfectly sized for the radio, so I decided to order one in unfinished aluminum. I ordered 3 to meet their minimum order price of $15, so if anyone in the Bay Area wants to buy one or two of these from me, just drop me a line.

Here’s the case with most of the front panel controls installed. I also fitted a red gel to the cutout for the frequency readout to improve readability:

and here’s the same case from the front:

A quick word about that rectangular cutout for the frequency readout because I know that some folk are put off by the prospect of cutting square or rectangular holes. The way I do it is by first punching or drilling a series of holes approx 1/4″ in diameter around the perimeter of the cutout to remove the bulk of the material.  I then finish it off with a set of fine jewelers files. To make the round holes, for my entire home-brewing career until now (a span of some 30 years) I would use a hand drill, and enlarge if necessary with an old screwdriver used as a reamer. Burrs would be carefully removed with a file. This method works, but can be time consuming, and doesn’t give as clean results as using a hand punch. A trip to Harbor Freight yielded this. I got the one with the imperial-sized dies – a set of both would be great. Making round holes with a hand punch like this gives a nice clean hole with no burrs – and in less time too.  It makes the whole process of preparing a case for a homebrew project all the more enjoyable. If you plan on embarking on at least a few more projects like this, owning a hand punch like this will make your life easier, and give better results.

Paradise – a soldering iron, a cup of coffee and a project to work on.  What more could a guy want?

With the rig finished, here are a few views:

You can see the 4 vent holes punched at the rear of the chassis just above the heat sink for the finals.  This particular way of doing it was suggested by Terry WA0ITP.  One extra bonus to having vent holes is that you can peek through them and see the cool blue LED that Dan put in the circuit to act as a low cost shunt voltage regulator 🙂

Note that although the radio is shown tuned to 3560, the 80M QRP frequency, if anyone called me on 3560 I wouldn’t be able to hear them.  This design utilizes a direct conversion receiver, so the station calling me would be at zero beat. The RIT gets you around that nicely however. I tuned the radio to 3560 for the “photo-op”, but when I monitor 3560, the readout shows 3560.5  as I like a 500Hz side-tone.

In the next view you can see the nylon nut, bolt and washer that I used to hold the VFO coil firmly to the board, to help make the VFO less prone to changing frequency when knocked. It’s not too apparent in this picture, but I used short stout leads to connect the polyvaricon to the board, also in the interest of VFO stability:

A view from the rear:

and finally, the regular view with the top on:

The toggle switch just to the right of the main tuning knob is a suggestion of Dan’s that was included in the construction manual. It switches in a 27pF NPO capacitor to give an extra range of tuning allowing the rig to cover approximately 90Khz of the band in two ranges, so that the tuning rate doesn’t get too coarse.  On this radio my tuning ranges are 35492 – 3547 and 3532 – 3589, giving me coverage of the bottom 89Khz of 80 meters in two tuning ranges.

The transmitted signal sounds great – nice sounding keying with no chirp or key clicks whatsoever; the transmitter doesn’t have that “homebuilt” sound! The real reason you want to build and use this rig though is because of the receiver.  The filtering makes it a really nice receiver to listen to; the design includes a 3 stage 7 pole 700 Hz low pass filter. There is also filtering to reduce mains hum – a common complaint with direct conversion receivers. As a result, with the transceiver fully cased up, I cannot hear any hum at all, even with the volume fully up. The other issue that occurs with DC receivers is that of microphony, and though it does occur with this receiver, it is minimal  and doesn’t impede enjoyment of the radio at all.

At this point, I’ve had no QSO’s with it, but that has nothing to do with the rig. It has more to do with my marginal antenna for 80 meters (to be improved soon hopefully), the fact that I’ve been busy building and casing it as opposed to being on the air with it, and also the fact that I get a great deal of local QRN on 80 in the evening, making it hard to use without a noise blanker.  If I can improve my antenna system on 80, then I’m sure that some early morning starts will net me QSO’s in the very early morning when 80 is still “happening” and the local QRN isn’t there.

Of course, homebuilt projects are rarely complete. I’m not sure if I’m even going to bother with painting the case and putting decals on it, as I kind of like the way it looks now, but I’d like to improve the rigidity of this low-cost Ten-Tec case with a couple of struts between the front and rear panels at the left-top and right top of the case.  I’d also like to find a better way of attaching the top cover to the chassis. Oh, and a small audio amp with a speaker mounted in the top cover wouldn’t be a bad idea either. However, it’s perfectly usable as it is and besides, I need to get out, socialize, and put the balance back in my life, and then work on my antenna system next week………

There is always something to work on and improve.  That’s the fun of operating an amateur radio station.  Many thanks to Dan N7VE and the AZScQRPions for this fine transceiver project.

February 18, 2010

Baby Steps at AA7EE

No major moves forward at the AA7EE shack recently, just a few little ones.

I’ve been eyeing a fairly tall tree (50-60 feet) that is right at the edge of the apartment building next door.  It’s just a few feet over the property line, and overhangs the small back yard of my apartment building.  With the aid of a slingshot, I attempted to get a line over it some months ago, but this is a built-up urban area and I didn’t try too long or too hard with the slingshot.  It was my first time using one (whatever DID I spend my childhood doing?) and I didn’t want to accidentally put a 1oz lead sinker through a neighbor’s window, or worse, hit a passerby. My initial attempts failed, I stashed the slingshot away and continued to use the Buddistick vertical from my first floor balcony.

The thing about tall trees though is that if you’re a radio amateur, unless you own a tower, they’re near impossible to ignore. Yesterday afternoon I gave in.  I grabbed the slingshot, walked out onto my balcony, took aim, and the next thing I knew the lead sinker had arced over a branch and was hanging just a few feet above the ground on the other side of the tree. Bingo!  It wasn’t as high up as I wanted, but if I had aimed it higher it wouldn’t have made it through the dense foliage to the ground, and a heavier sinker wouldn’t have made it as high in the first place.  It’s a regular catch 22.

Long story short – with the aid of a reel of 26 gauge magnet wire, I now have an approximately 65-70 foot longwire antenna about 35 feet off the ground. The magnet wire will keep my antenna relatively stealthy (I hope). It’s still a pretty crummy location for an antenna, but at least I now have frequency agility with the aid of an LDG Z11 tuner and 4:1 balun.

In other news, I finally fitted a KD1JV Digital Dial to my Norcal 2N2:

This is a really worthy upgrade. The only other thing that this rig could use now is a small electronic keyer. Here’s another view in which you can see the 100 ohm resistor and 100uF electrolytic mounted at the power connector that serve to filter out the low level interference from the display multiplexer:

The 2N2 is an absolute pleasure to listen to.  The only commercial rig I have is an FT-817, and when I use that for the other HF bands, I cringe at the high level of noise generated by the receiver. The receiver noise in the 2N2 is much lower.  There is a clarity to signals heard on the 2N2; in comparison the FT-817 sounds noisy and mushy (it is a great jack of all trades radio though and has served me well).

I also started putting the Fort Tuthill 80 into a case.  A KD1JV Digital Dial should be arriving soon and will be fitted, along with decals (probably yellow, to contrast with the black, as inkjet printers won’t print white).  Here’s a view of the Tut80 without it’s top cover.  Imagine this with a digital frequency readout and yellow decals.  I think it’s going to look pretty sweet:

I’ll save the top view until I’ve tidied up the wiring inside a bit so stay tuned.  John AE5X is waiting on a Ten-Tec TPB-41 case to put his in, and I’m keen to see how he does with it in the ARRL International DX Contest this weekend (if the case arrives in time that is – if it doesn’t, how about a bit of bare board operating eh John?) While we’re talking about cases for the Tut80, Steve KB3SII has designed and is manufacturing a custom drilled and painted aluminum case for it.  Target price is under $35. Check the Tut80 Yahoo Group for more details.

I’ve been trying to get a QSO with the Tut80, but the electrical interference in the evening at this location is so bad on 80 that I can’t hear much without a noise blanker. Oh for a nice quiet radio QTH…….

In the meantime I’m searching for a new living situation. There are two main criteria – affordable rent, and the ability to string a longwire antenna to nearby tall trees. It’s time for me to experience the amateur bands with something more than a marginal antenna. I know that I could probably move away from the San Francisco Bay Area and buy (or rent) a little place on a big piece of land but, for the time being at least, I want to stay in this area. So if you know anyone with a cheap room or studio to rent in the Bay Area that would be amenable to a friendly and quiet QRP operator, send ’em my way!

February 9, 2010

The Fort Tuthill 80 – A Direct Conversion Transceiver For 80M

A week ago, the Arizona ScQRPions released their Fort Tuthill 80M TX/RX kit. I’d been keen to build it ever since I became aware of it (thank you AE5X) due to a long standing interest in DC receivers, and the fact that the first transceiver I ever built was also for 80M and also utilized a DC receiver. That was back in the early 1980’s.  I brought that rig with me to the US when I moved here from the UK in 1987 and then fried several of the active devices in it by accidentally connecting the power the wrong way round.  Yes I know – for some reason I didn’t want to use a diode to polarity-protect it (probably didn’t want to lose the 0.6V forward-bias voltage drop).  At the time I was going through a phase of my life in which I was distinctly uninterested in amateur radio, so rather than replace the fried devices, I threw the whole thing out and somewhat regret that decision to this day.  I don’t remember it suffering from any of the problems normally associated with DC receivers – microphony and hum pickup. However, this could very well be a case of my looking through the past at rose-tinted glasses.  As it was the first transceiver I had ever built, it was the apple of my eye, and well, proud parents can be quite good at ignoring flaws in their offspring.

OK, here’s what you get for your $53.  The silvery bag contains the active devices, and you also get 2 sets of decals:

Considering the amount of work that goes into designing something like this, designing the PCB, sourcing and ordering all the parts, as well as bagging them all up ready for delivery to you, the end consumer, $53 is a steal. Dan N7VE, the designer of this transceiver, knows a great deal about active filtering in receivers and has applied his expertise and knowledge to the design. Look here for a presentation he gave on the subject of active filtering in receivers.

A closer look at the board that Dan designed for this radio:

One of the many great things about the internet is that manuals for kits can be more detailed, with more pictures than ever before.  Dan’s manual makes building this little radio a lot of fun, and with the help of the Yahoo Group, expert advice from the designer, or other builders, is not far away.

The build went smoothly.  As tends to be the case with these things, I stayed up all night to finish it off and ended up finally hitting the hay at 9am.  I find that it’s easy to get so engrossed in a project that I’ve barely noticed that it’s something like 3am.  By that time I’m within spitting distance of finishing – or so it seems.  I’m not fast at doing things, tending to get distracted easily by things like the need for coffee breaks, the urge to look at something on the internet etc, so what some might call an 8 hour kit build, is closer to 3 times that for me. Next thing I knew it was 9am, but the board was finished, and all the external connectors temporarily connected:

The board with external connectors temporarily attached. On the far right just above the middle you can see the 2 PA transistors epoxied to the heatsink. Just above that is the trimpot for controlling output power. The VFO toroid is on the far left about 2/3 of the way up the board.

Initial impressions are favorable. Although some of the capacitors are microphonic (to be expected in a DC receiver), I can tell that this is not going to be a problem in use, especially when the board is mounted on standoffs in a case.  The other main problem with DC receivers is the issue of hum pickup.  I’m a little concerned, because I am getting quite a lot of hum pickup through the antenna connection. I’m hoping that enclosing the board in a metal case will help.  An enclosure will be arriving later this week, so we’ll see how that helps.

The receiver is sensitive and VFO stability seems to be good enough for regular usage.  Using my FT-817 as a reference,  I measured about 60Hz of drift in an hour from the VFO after it had already been on for several hours, operating in a room of reasonably constant temperature. I then measured the frequency drift every hour for 6 hours. After 6 hours, the VFO had drifted 90Hz higher than the original frequency; the maximum drift from the original frequency within the 6 hour period was 150Hz. Not bad! I intend to fix the VFO toroid more firmly to the board with a nylon nut, bolt and washer to help improve the resistance of the VFO to physical impact.

At this point, my main concern is that of hum pickup in the receiver.  We’ll see what happens when I’m able to install it in a metal case. To be continued………..

Postscript – nothing better to do with my time this morning than stare lovingly at the PC board and ponder on what a thing of beauty it is:

The board after disconnecting the temporary knobs, switches, power etc and before mounting in a case.

Hum Problem Solved – I haven’t begun to put the FT80 in a case yet, but the hum issue has already been resolved.  The radio was connected to an antenna via an LDG Z11 tuner, which was powered by an unsmoothed wall wart transformer.  On unplugging the wall wart from the wall, the hum all but disappeared.  There is still a very low level of background mains hum, but only at the level you’d hear in a mains powered receiver with a well smoothed power supply. At this point, the radio is very usable in just the current bare board situation; things can only get better when it is installed in a metal case. Dan N7VE made the point that if you mount the board close to the bottom of the case, as the traces are on the bottom of the board, and the top of the board is mainly ground plane, then the traces will be sandwiched between two ground planes. The FT80 looks like it is going to be a very usable little transceiver. I’m really looking forward to when QRP Kits start stocking versions for other bands.

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