Month: January 2021

An End to the HDR – SDR Conflict? Kevin AA7YQ Combines the Best of Both Worlds

We’ve had some pretty amazing contact with Kevin AA7YQ over the years. Kevin and I originally bonded due to our common experience with parachutes (he was smoke-jumper, I jumped while in the army). Kevin once used a parachute to insulate a QRSS beacon. And one day, while thinking about SolderSmoke during a drive through Montana, Kevin turned on his rig only to hear… ME! He caught one of my infrequent CW contacts. TRGHS.

Now we hear that OM Kevin may be poised to end the HDR-SDR civil war that has for so long been dividing our great podcast. Can Kevin’s new rig heal our wounds and allow us to enjoy the beauty of SDR waterfalls while not forsaking the joy of hardware defined rigs? Kevin will soon launch a blog describing his effort at rig-building. See below for a preview. Stay tuned.

Kevin wrote:

I am currently working on a new rig design. It is a hybrid HDR(Hardware defined)/SDR radio that incorporates some classic superhet design along with some of the more useful features of SDR. I have found that pure SDR is really not that enjoyable for me. I love using GNU radio to mock up and test design concepts, but SDR basically dilutes the “magic” of radio to nothing more than software and touchscreens, stuff we use every day all day. Its not the Ham Radio I grew up with as a kid and was fascinated by. On the other hand, I have always fought temperature drift, large variable capacitors minimal tuning range, and associated with classic VFO and VXO designs. In fact, in 1997, for my senior capstone design in EE at Montana State University, I designed a 20m superhet that used a DDS LO. At the time DDS was cutting edge technology I used an AD7008JP50. I had to beg and plead with ADI to get a couple samples for my design, since they exceeded my self-funded college student project budget. 😊 But that’s another story. SDR has made me grow extremely fond of the waterfall display. I love having the visual “situational awareness” of what is going on in a moderate bandwidth outside of the spot I am tuned to. I also am a big fan of digital filtering and modification-ability that comes with boot-loadable microcontroller designs. So this design includes most of the real highlights of SDR but does not take the fun out of designing, building, and operating a HDR.

Anyhow, this design is a big goal of mine to complete and build in 2021. I am not retired yet so I still have to balance, work, family, and tinkering time, but I am very excited about this project. I have “noodled” this design to the point of what I have achieved full-on “analysis paralysis”. That is, I keep designing and redesigning, optimizing, and figuring to the point where after months of thought, I have nothing to show for it 😊. So my New Years goal for 2021 is to make “good enough” rather than “perfect” design decisions and move forward. I will keep you posted on the design and possibly start a blog so I can get some peer review input from the greater RF Design/Homebrew community on my project. I’ll keep you informed on my progress.

Glowing Numerals for the Lafayette HA-600A (With Jeweled Movements)

I really like this receiver. I have strong sentimental ties: it was my first SW receiver. But the frequency readout situation was kind of rough — depending on where you put the Main Tuning cap, your Band Spread dial could be WAY off.

China to the rescue! Specifically the very nice San Jian PLJ-6 frequency counter boards. I have used these in several projects. I like them a lot. I get mine on e-bay. They are very cheap. Here is the manual with specs:

https://www.mpja.com/download/35057tebasic%20manual.pdf
As I did with my BITX20, I put mine in an Altoids-sized box. I got to use my Goxawee rotary tool with circular metal blade to cut the rectangular hole. Hopefully future efforts will yield neater results, but the flying sparks were fun; they made me feel like one of those car-part “fabricators” on cable TV.

To tap the VFO frequency, I just put a bit of small coax at the point where the 10 pf cap from the VFO circuit enters the first mixer. I ran this cable to the unused “Tape Recorder” jack on the back of the Lafayette — this connects to the input of the counter. I attached 11 volts from the power supply to an unused terminal on the accessory jack of the Lafayette — this powers the counter.

Having a counter on the VFO proved very illuminating — in more ways than one. I measured the Center Frequency (CF) of my IF to be at 456 kHz. I set the PLJ-6 to display the VFO frequency MINUS 465 kHz. For AM broadcast signals, this worked fine: I’d tune the signal for peak S-meter reading. This meant that the carried was right at the CF.

For SSB, things were a bit different. I set the BFO knob to be RIGHT AT 465 kHz when the dot is in the center position. With the BFO there, I could tune in SSB signals. The suppressed carrier would be right at the center of the IF passband, with the audio information above or below the suppressed carrier frequency. But it didn’t sound good this way — it sounded better if I would tune an LSB signal 2 kHz down from the center, then adjust the BFO down about 2 kHz. This put most of the the audio in the peak portion of the IF filter(s) curve. Doing it this way means that I have to remember that the number displayed on the PLJ-6 is 2 kHz down from the actual suppressed carrier frequency of the transmitting station. I can live with that.

I am going to leave the Lafayette on the corner of my workbench so that I can easily tune in hams and SW broadcast stations. Having modified the product detector and added the digital frequency readout makes listening to this receiver even more pleasing. The jeweled movements are as smooth as ever.

So 2021 is off to a good start on my workbench. HNY to all!