Dave Richards AA7EE

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 23, 2010

A New Antenna Opportunity

Filed under: Uncategorized — AA7EE @ 5:51 am
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In my last post I alluded to the fact that big changes to the antenna situation here at AA7EE could happen soon.  I’ve been painfully aware that my antenna just ain’t cuttin’ it.  It’s not the antenna (a Buddistick vertical, and more recently a 65-70 foot longwire as well) it’s the fact that it’s mounted on my balcony with the feedpoint at 20 feet above ground, giving me a reasonable take-off to the west, a bad take-off to the north, average take-off to the south and absolutely abominable take-off to the east, which as I’m in the San Francisco Bay area, is most of the rest of the country.

Today, the owner of my apartment building indicated that he would be open to my placing a 31 foot vertical on the roof of the building provided that a) it doesn’t break any local ordinances and b) he’s satisfied that it isn’t going to fall over and hurt or annoy anyone.  Just as I was looking around for a new place to live, I get the carrot from him that might tempt me to stay! To help explain the situation, here’s a cross-section of my apartment building, showing my apartment and the location of the current antenna on the first floor, as well as the proposed location of the new antenna. This new antenna, as well being about 35 feet higher than the existing one, would give me a pretty good take-off in all directions – a major breakthrough:

The antenna I’m considering is an S9V 31 foot vertical with a bunch of radials lying on the roof and an ATU located at the base of the antenna with 50 ohm feed going back to the “shack”. I’m pretty excited about this as I think it will be a great improvement over the current antenna location. Tomorrow morning, I’m grabbing a ladder and heading out onto the roof to do a bit of research. At the very worst, I’ll get a great view of the City of Oakland, but I think this is going to be good.

If anyone has alternative antenna suggestions, I am very open.

February 22, 2010

The 2010 ARRL International DX Contest

I’m not going to take any prizes in this year’s ARRL International DX Contest; I only had 32 QSO’s. However, it was a lot of fun, and well worth the time and effort I put into this very casual approach. Firstly, I’m no contest operator; my reliable CW copying speed is no faster than 15 wpm, my antenna is marginal at best (a 65-70 foot longwire strung out of the back of my first floor apartment to a nearby tree, and blocked to the east and north by tall trees and my apartment building), my signal is just 5 watts, and on top of that, I have almost no serious contest experience, and it shows!

The great thing for me about a big contest like this is that there are thousands of very experienced operators the world over all listening for my signal. Many of them have first rate receivers and excellent antenna setups in ideal locations, and they are all listening for me – much more intently than the average non-contest operator who is calling CQ and just looking for a casual QSO or a chat. What an ideal way to see where on the planet my little QRP signals are being heard.

In the first hour of the contest,  my head turned to mush. The operating was frenetic, and much of the sending even faster than normal (beginnings and ends of contests are often like this). The cacaphony of signals on the bands had me wondering if I had really learnt morse code at all, or if that had all been a dream, because all I was hearing were impossibly fast dits and dahs that seemed to carry no intelligent information. It was all a bit dispiriting until I calmed down and started to get the hang of it.

I’ve heard people say that they’re afraid to try big CW contests because the operating speeds are too fast for them. Once you’ve sat and listened for a while though, you realize that most contest exchanges consist of just a few well used and oft repeated terms and phrases.  On top of that, if you don’t get a station’s callsign properly, you can just sit on his frequency and keep listening as long as you want until you get it right.  The poor chap who is calling doesn’t have that luxury; he has to copy your callsign correctly the first time you send it (or the second time if he asks for a repeat). For a start, you KNOW that the other guy is going to give you a 599 report ( I disagree with this practice and like the fact that smaller QRP contests such as the NAQCC Sprint urge participants to give accurate reports). You also often know what the other part of his report is going to be by listening to him QSO’ing with other stations.  In the case of the ARRL International DX Contest, the second part of the exchange consists of the 2 letter abbreviation for the state for stations in the 48 contiguous states, and the power for all other stations; if you’re hearing a loud non-US station, chances are he’ll give you 599 KW, or simply 599 K indicating that he’s running somewhere around 1,000 watts, give or take.

So you’ve listened a bit, you’ve finally figured out the other chap’s callsign by listening him send it at 40wpm about a half dozen times (which is what I did much of the time), you also know he’s going to give you a report of 599 KW. All that’s left is to make sure you know how to send your callsign, and how to send 599 CA (or a different 2 letters, depending on where you live.)

Here’s a typical exchange in the ARRL International DX contest

(other guy) JA0JHA JA0JHA test

(you) AA7EE

(other guy) AA7EE 599 KW

(you) 599 CA

(other guy) tu JA0JHA JA0JHA test

and there he’s off, about to work another station. If he doesn’t hear your callsign properly, he’ll send the few parts that he did hear, and then send ? like this:

7E ?

which is your cue to send your callsign – perhaps this time to send it twice to help him copy it.  That’s it – don’t send anything more – no extra phrases, like “QSL OM?” or similar. There’s no need for it.  If he didn’t get your report, he’ll send the following:

nr ?

This is your cue to send the second part of your report (twice in a row to make sure) – no need for you to send the signal report because he knows that you gave him a 599.  I don’t like this but it’s the accepted custom, so I’m going to act like a sheep here because I want to get myself in his log.

That’s about it really.  There are one or two other things, but you learn them as you go along.

Pretty easy isn’t it – and for that small amount of effort, you have at your disposal thousands of well-trained radio operators with first class setups in some of the world’s best radio locations all listening for your signal, and if not prepared to give you an accurate signal report, at least prepared to acknowledge that they heard you.

It’s brilliant – and that’s why I like contests. It was a bit depressing at first because I called a lot of people who didn’t respond, but I had to remind myself that if a guy was running full legal limit and was registering less than about S4 on my meter, he very possibly wasn’t going to hear my 5 watts at all. On top of that,  in the first hour or two of a contest,  everyone is going crazy trying to work each other, and the QRP station with a so-so antenna doesn’t even get a look-in. I noticed that an hour or two into the contest, everyone seemed to settle into a brisk yet more measured pace.  That and the fact that I had started to get the hang of things meant that I managed to make a few QSO’s.

In all, I spent a few hours of the 2 days at the radio.  I did a lot of listening, and a little bit of transmitting.  I made 32 contacts of which the majority were with JA land, a few were with Stateside stations, one with Hawaii, one with Asiatic Russia and one (my favorite one) was with CR2X in the Azores Islands.  I made the Azores Islands on 5 watts. Awesome!

The moment the contest ended the bands went back to being fairly silent. If you’re not seriously contesting, it’s worth stopping your operating a minute before it ends so you can be tuning around as the end time rolls around. Hearing bands go silent at the end of a major contest is a weird thing to experience. All those thousands of high powered transmitters the world over ceasing transmitting within a minute of each other.  Bizarro……

QRP can be hard work, and with a compromise antenna, it is harder work still.

I think though that my antenna situation is about to improve dramatically.  More about that in a future post.  I don’t want to jinx things…….

How did you do in the contest?

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.

February 1, 2010

Radio Shack Saved My Life Tonight (With Apologies To Elton John)

Radio Shack (I cannot bring myself to call it “The Shack”) has never been my first port of call for electronic components and associated items, but when I was a teenager in the 1970’s and went shopping in Worcester with my Mum (Worcester, England, as opposed to the one in Massachusetts) I’d hit up 2 places for parts for my latest electronic building project.  There was a mom and pop electronics parts store on Foregate Street (I think), and if they didn’t have it, I’d try Tandy (as Radio Shack is called in the UK). Back then they actually had quite a lot of discrete components. It was often possible to find a schematic for some simple project in an electronics magazine (lie detector, light dimmer – that kind of thing) and actually get all the parts for it from Tandy.  Wow – think of that.

As we all know, Radio Shack is carrying less and less stuff of interest to the electronics hobbyist.  I don’t blame them; it’s a shrinking market. I rarely even consider going there for parts now. But this evening I decided to take a look at the KD1JV Digital Dial kit that had arrived from Hendricks QRP Kits a week earlier with a view to putting it together.  The instruction manual recommends .02″ diameter solder to help with soldering the SMT devices instead of the usual .032″ size. I’ve been making do with .032″ diameter solder but knew that I actually wanted to try using some nice thin solder for this kit.  It was 6pm on Sunday evening. Where was I going to get .02″ diameter solder? The instructions mention that Radio Shack carry it, which surprised me, because my local electronics emporium, Al Lasher’s in Berkeley, doesn’t.  A quick phone call to the local RS revealed that they did indeed have a roll of the stuff in stock.

I realized that my bike had a flat rear tire (I don’t own a car), changed the inner tube, and got to the store at around 6:30. Had a quick chat with the employees there and got back home, solder in hand, at 6:51. I didn’t think I’d have occasion to say this nowadays, but a big thumbs up to Radio Shack.  I bet their employees haven’t heard of SMT devices, but their store certainly carried the solder to work with them.

How much longer before RS don’t carry anything I want………maybe not long but they came up trumps this evening.

(Incidentally, Al Lasher’s is a really great place for discrete electronic components with good old-fashioned personal service, if you’re ever in Berkeley, CA. The fact they didn’t have this one item is no big shakes.  There have been so many other times they had exactly what I wanted.)

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