Archive for July, 2011

Improving 50-MHz Transmit Capability

July 28th, 2011

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.

Improving 50-MHz Receive Capability

July 23rd, 2011

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…

SoftRock v9.0 Lite+USB Xtall QRV

July 23rd, 2011

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.

Revisiting the 50-MHz Transverter

July 17th, 2011

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.

Field Day W3AO/KE3Q QSO standings

July 10th, 2011

As I wrote previously, for 2011 Field Day, I made a game of trying to contact W3AO and KE3Q on as many bands and modes as possible.  Here are the official standings from KD4D who managed the PVRC competition:

Call HF 6M 2M UHF GOTA Digital Satellite Total
K1DQV 11 2 2 2 0 3 0 20
K8GU 11 0 1 4 1 1 0 18
W3GG 12 1 0 0 0 5 0 18
K1HTV 10 2 2 0 0 3 0 17
NA3M 12 0 0 0 0 3 0 15

So, K1DQV was at the top of the heap (with a 2-meter CW contact, I might add).  Anyhow, I’m quite pleased with the results and happy to report that W3AO is claiming the all-time high QSO total for Field Day this year.  Congratulations.


New Arrival

July 10th, 2011

Early Monday morning, the day after Field Day, we welcomed our son Evan into the family.  We were so right to stay home!  As good friends have opined “your life will change…for the better.”  So far, I would tend to agree.  The blog will receive (even more) infrequent updates, K8GU may be a little less active on the air, and there will be fewer homebrew projects over the next few weeks and months.  A few months ago after building some UHF antennas when I pinched the palm of my hand with a pair of pliers, I watched the blood blister heal and commented to Sarah on how amazing it was for several days straight.  “You think that’s amazing?  Well, I’m growing new life inside of me.”  We laughed, but it’s very true.  Every day is something new:  grasping, gazing, grunting, and gurgling.  This is only the beginning.  That’s pretty amazing.