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Last night, as I have been doing lately in both the evenings and mornings, I was trawling the bands with a SoftRock (a dual-band v6.0 built for 40 and 80 meters—my first SoftRock) and Rocky.  Without fail, the waterfall enables me to see something interesting, which brings me to the point that I really need to integrate these receivers into my station.  But, I digress.  The really tantalizing, fascinating signals are the weak ones, especially when they are weak and unusual.

The subject weak and unusual signal is shown in the figure headlining this post.  Rocky’s cursor shows the approximate bandwidth of the CW filter (250 Hz, if I recall correctly) and the center frequency (7026.25 MHz).  I tuned it in and caught a CQ from “AA1T…”  Recalling that I head read about Mike, AA1TJ‘s, Das DereLicht transmitter built mostly from parts scavenged from a dead CFL, I suspected it was him.  After a moment the QSB came up and I caught the ‘J.’  Thanks to the fact that the SDR is not fully integrated into the station, I scrambled to plug my 15-year-old Small Wonder SW-40 in and get it online.  Mid-scramble, Sarah handed Evan off to me for a diaper change, but I did manage to snap the screenshot above.  By the time I returned to the shack awhile later to close things down, AA1TJ had disappeared.

Through the (ubiquitous) magic of the Internet, I sent Mike an apologetic e-mail QSL, which yielded a nice response.  It turns out that he was trying a 40-meter version of the first transistor transmitter described in the amateur literature.  The design for 146 MHz by K2AH appears in March 1953 QST.  If you are an ARRL member, pull up those old QSTs in the archives and read about it.  K2AH is on the cover of February 1953 QST with the same transmitter.  Mike figures he was making 20 mW, or 20650 miles/Watt on the path from his station to mine.  The more remarkable thing is that he was using a 1956-era point-contact transistor (the same type as in the K2AH article).  Fascinating stuff!  Hopefully, we’ll connect for a real over-the-air QSO sometime soon.

Thanks, Mike, for making my day by doing something interesting and sharing it on the air!

Over the past week in the evenings, I’ve managed to cobble a little PA together for the 50-MHz transverter.  It’s a near-clone of the PA in the Elecraft XV50 using the Mitsubishi RA30H0608M.  Last night, I got it all hooked up and installed in the cabinet.  It broke into oscillation when keyed on CW.

The oscillation was about 50.040 MHz.  I reasoned that it might be the PA output coupling into the nearby TX RF bandpass filters which are followed by 12 dB of gain before returning to the PA.  So, tonight, I added a litle shield between the BPF and the PA board.  That seemed to clear things up and I got about 10 watts out.  There is a 6-dB pad between the last driver stage and the PA, so I should be able to get it up to about 18-20 watts.  But, the first goal will be to check the linearity on SSB.

In other transmit capability news, some boxes and heatsinks arrived for the W6PQL PAs for 903 and 1296 this afternoon.

As I mentioned previously, the receive capability in my 50-MHz transverter seemed to be a little bit anemic.  So, I decided to add a little bit of gain.  Looking at the block diagram for the transverter (shown below in updated form—jumper across the SGA-4586Z to understand what the circuit looked like initially—by the way, full-sized PDF versions of all of my notes and schematics will eventually be available here), I reasoned that I had the following losses and gains:  +10 dB for the LNA (this might be as much as +15 dB, but 10 seems more realistic, if not generous), -3 dB for the bandpass filter, -7 dB for the mixer conversion loss, and -3 dB in the diplexer, leaving me with -3 dB overall conversion gain.

So, I endeavored to find some more gain in the form of a MMIC (which is really what all gain blocks in this transverter would be if I were to do it again).  I have a nice (but dwindling) supply of SGA-4586Z’s that produce about 20 dB gain with a 1-dB compression point around 16 dBm, which is probably a good part for this location.  The idea is to overcome the losses in following stages with robust gain in earlier stages (in order to keep system NF low).  So, I ripped out the existing two-pole BPF and replaced it with this:

I was relatively satisfied that I had everything working with the cover of the transverter off to peak the BPF on the W3APL beacon.  So, I replaced the cover and surprise!  To borrow a poetic description of RF circuit doom from N3UM, the MMIC “amplifier burst into song.”  Bursting into song is a bit of a charitable description for something that sounded more  like S9 power line noise in the IF receiver.  I did not actually know that it was the MMIC oscillating at first, but I started wiggling cables and finally found that if I touched the 12RX (+13.8 volts on RX) line, the problem disappeared.  So, I added the 0.01-uF bypass capacitor to ground on the supply side of 180-ohm bias resistor and the problem was solved.

With the completion of the HF SoftRock with Si570 LO, I now have a tunable IF to play with the transverter.  We had a nice opening to the Southeast and Gulf this morning and I even heard my first DX with the transverter and SoftRock combination—CO2WF.  With the appropriate software, I can configure a the SoftRock as a panadapter with the TS-930S as the transmitter.  More on this in the future.  Best of friends:

The real next step in making the transverter useful is building a 20-watt PA stage.  This should be good for driving a Mirage or TE Systems brick or even something bigger like a 3CX800 or 50-volt solid-state amp…

Got the SoftRock v9.0 Lite+USB Xtall working last night.  I’m not 100% sure what the problem was, but I think it may have been due to me programming an ATTiny85 with the latest SoftRock firmware (V15.14), rather than using the supplied ATTiny45 with V15.4.  So, I’m sticking with old version for now.  Not sure if it was cockpit error on my part programming (more likely) or an incompatibility with the new firmware which is designed to work with the Ensemble series of SoftRocks.

As shown in the screenshot from Rocky above, there appears to be a spur that repeats every 1 kHz (see left side of the waterfall).  The right side of the waterfall is with the USB cable unplugged from the computer.  I’m 99% certain this is something internal to the SoftRock because I wrapped a few turns of the USB cable around a big type-31 ferrite toroid and the spurs are still there.  So, need to play with that.

I’m listening to a Es opening to the south on 50 MHz right now using the SoftRock as the RX IF.  Yes, that means that I got the RX on the transverter souped up a little hotter.  I will post something about that later today and place a non-causal link in this post.

I recently resurrected the 50-MHz transverter project and have made good headway getting it working.  On Friday night, I began the process of tapping holes in the PA module heat spreader.  But, despite using plenty of “cutting fluid” (3-in-1 oil), I managed to break a (well-used) tap on the first hole.  Since the maximum (linear) power out of the driver stage is 200 mW, I embraced my inner QRPer and put the PA project aside to give the transverter a try in the CQ WW VHF contest.

The 6-meter Yagi had come down in favor of Yagis for 222 and 432 when the loaner FT-736R showed up.  So, I scampered up onto the roof and moved Yagis around.  I had hoped that this moment would be accompanied by changing out RG-8 coax for LMR-600 and LDF4-50A that are taking up space in the shop and shack.  But, I was not ready to commit to cutting that and I still don’t have LMR-600UF for the rotator loops.  Plus, I should replace the rotator at the same time.  That amounted to too much work for the available time.  I really just need to bite the bullet and install a rotating mast for the VHF antennas that’s not so precarious.

Got everything hooked up late on Saturday afternoon, but had to tend to some domestic concerns and was QRT until later in the evening when I heard my neighbor W4EE calling CQ on six SSB.  Did not know that he had six!  Apparently, this is a new thing for him, too.  He was surprised that I didn’t vibrate his radio off the desk like I usually do!  Told him I was running 200 mW and everything made sense.

Ended up working a few other locals on Sunday including N3UM, who moved me from 6-meter CW to 2-meter SSB for a quick chat.  He just completed the N1DPM active bias mod to his Mirage B2518G, so was eager for an audio report.  Sounds good!  He said my B3016G sounded good on-frequency, but I haven’t gotten the mod actually inserted into mine yet.  Probably that Kenwood (TS-700S) audio making up for the amp’s inferiority…

Eventually, I will be posting more details on the circuit here.  This is one of those projects that I would not encourage anyone to duplicate as I have constructed it.  However, there may be useful features.

Brian, ND3F (aka N3IQ/R), gifted me a partially-complete SoftRock kit a few months ago on the condition that I put it on the air.  I’m making some progress on that.  I took this photograph to show the SparkFun USB break-out board installed in the Bud CU-124 enclosure.  The whole thing is assembled now, but there is probably a solder bridge somewhere.  This kit is going to be a lot of fun because it’s actually more flexible for experimenting than the present Ensemble II RX kit.

This is about building electronics, not making beer, at home; although, I am sure there are parallels.  Three things brought me to writing this:  1. an eHam forum thread I responded to a few weeks ago;  2. the June 2011 issue of IEEE Microwave magazine (has articles by K2UYH, N2UO, and KK7B, perhaps others? thanks to W3KL via the PVRC reflector for bringing it to my attention since I let my IEEE/MTT membership lapse); and 3. a few minutes spent last night resuming a partially-completed Softrock kit gifted to me by a friend who decided to buy a FLEX-3000 instead.

Every once in a while, a thread appears on an amateur radio forum that goes a little bit like this, “Hi, I’m a new ham and I don’t have a lot of money to spend so I want to build an HF SSB station from scratch” or something similar. Somehow, somewhere, somebody has given the impression that it is less expensive to build your own amateur radio equipment than to buy it.  That’s true in some circumstances, but certainly rarely for anything that is mature, mass-produced, and readily-available on the second-hand market.  After all, there is nothing novel about a 100-watt superheterodyne HF SSB transceiver these days. The principal uncounted cost is the “engineering cost” associated with getting your first few projects working and keeping them working.

One of the first construction projects I undertook as a new ham was to build a Ramsey Electronics HR-20 (NE602-based) 20-meter receiver—$20 at a hamfest.  It did actually work eventually—but this was a simple kit with maybe two dozen parts.  Next, I built a ONER transmitter kit from now defunct 624 Kits.  I think that was another $20.  I never made any QSOs with that combination because I was always afraid of blowing out the receiver with the transmitter.  The first thing that I built that I actually managed to make a QSO with was a Small Wonder Labs SW-40, which I still have.  That set me back $55 and it did not work immediately.  Suddenly, that’s over $100 by the time you include the money I spent on a soldering iron and solder.  That’s one-third to half-way to a “real” used HF transceiver and I had two bands at 1 watt on CW only.  Furthermore—these are all kits—they leverage economies of scale in purchasing parts from various vendors and they have instructions to help you along.  And, I’d like to think that I was a relatively representative example of a recently-minted ham who had more ambition than money or skills…

As I soldered down 1206-size (easy ones) SMT capacitors last night, I was thinking of times that I rushed through a homebrew or kit project just to get it on the air.  In those instances the process was often, as I have belabored above, about saving money, not about the act of creating something.  Last night was about creating, not saving, and that is the joy of homebrew.