Dave Richards AA7EE

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!

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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.

January 11, 2010

Software Defined or Hardware Defined – Which Way to Go?

The main project going on in the AA7EE  “shack” (for which read “main room of my studio apartment”) has been, and will continue to be, the monumental task of committing my sizable collection of cassettes, CDs, DAT tapes and broadcast carts to backed up hard drives.  This is an ongoing project which I expect to take several years. Over the course of a 22 year career as a DJ, I amassed a lot of stuff that is becoming wieldy and expensive to lug around, so it’s time to start consolidating.

So whenever I’m listening to the radio or soldering something, I’m often also ripping a CD, scanning the artwork, or calling up my friend Antoinette and trying to give her as many of the CD’s that I just ripped as possible. I spent 22 years accumulating stuff (opens in a new browser window) and I now want a good portion of it gone (thanks Antoinette!)

All that aside, the amateur radio goings-on here have included building a neat little direct conversion receiver for 40M – the VRX-1 designed by NT7S and sold by the 4SQRP club. It’s a cool little DC receiver.  I’ve been having a bit of a problem with the input bandpass filter, so it’s on the back burner for a while, but it’s been a fun Manhattan building experience:

NT7S’ fun DC receiver got me all charged up.  The first successful TX/RX I ever built was an 80M DSB TX/RX designed by G4JST and G3WPO and published in the UK magazine “Ham Radio Today” in March 1983. It utilized a direct conversion receiver, to which I added an audio filter built from a 741 op-amp.  It was my first experience with DC receivers, and I remember being surprised that such a simple receiver could sound so good. Jason’s VRX-1 re-introduced me to the pleasures of DC receivers, as well as the technique of Manhattan construction (my first time), so by the time I’d finished construction, I was all primed up and ready to swoon at any direct conversion receiver that might flit it’s tail feathers at me.

John AE5X’s post couldn’t have come at a better time. Allow me to repost this picture of the 80M direct conversion TX/RX that the Arizona ScQRPions will be providing a kit for very soon:

The details are here. I was beyond excited when I found about this (thanks John).

I have a mental list of several different QRP rigs that I want to build, among them the Weber Dual Bander, and either the Elecraft K1 or K2. However……SDR has been on my mind too recently.  I built the SoftRock Lite II for 40M a few months ago and was impressed with the performance for such a simple piece of hardware, and low price too.  Of course, the simplicity of the hardware and the low price is a bit misleading because the signal processing is all done in software.  This is the beauty of SDR though – if a better demodulator or filter is available, you just download it.

I’ve been using the SoftRock to monitor the CW portion of 40M, and then once I see a signal, I can work him on the main rig, which is currently a Norcal 2N2/40.  Yesterday, I built a combined switch and dummy load into an Altoids-type tin so I can easily accomplish switching the antenna between the SoftRock and the 2N2/40.  The 2N2/40 is a cracking little rig – a sensitive low-noise receiver with a stable VFO (after the intial warm-up period).  It has a nice narrow crystal filter too which is great for working people, but not as convenient when you’re trying to find stations to work.

So….what I do is use the SoftRock to look at a wide portion of the band.  With my soundcard, I can look at a 96KHz-wide slice of the band on my screen, and the minute I see a station, flip over to the 2N2/40 and work him. It works well but it got me to thinking – why switch over to a traditional radio to work a station that I find with SDR? Why not just get an SDR transceiver and avoid having to switch over to a hardware defined radio?

Hardly original thinking.  I’m sure it’s the same thought process that has led many an amateur to adopt an SDR rig as their main station radio. FlexRadio are about to introduce their Flex-1500, which is a 5 watt all HF band SDR transceiver.

Mighty tempting and with my limited amateur radio budget, I’m now wondering whether to continue building all the QRP transceiver kits I’ve had my eye on, whether to build the SoftRock v6.3 HF TX/RX, or whether to go for broke and get the Flex-1500 when it comes out.

In the meantime, I have a KD1JV Digital dial on order, which will turn the Norcal 2N2/40 into an even more usable little radio.

Oh, and I have 1,000’s of CD’s to rip and perform hi-res artwork scans.  It’s not as if I’ll be sitting here twiddling my thumbs.

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