Grayson Evans KJ7UM on the Ham Radio Workbench Podcast

 

OM Grayson was on the HRWB podcast with George Zaf and company. This was a really informative and entertaining session.  For example, when asked if special precautions are needed when working with thermatrons, Grayson replies, "Well, try not to swallow anything... and don't sit on the thermatrons."  Words to live by my friends.  Grayson's story about cooking Tektronix scopes in a refrigerator re-purposed as an oven (after cleaning the 'scope with a Home Depot power washer) is the kind of practical advice that readers of this blog REALLY NEED!  

But seriously, I learned a lot just listening to Grayson talk about thermatrons with George and the HRWB crew.  

The interview includes nice shout-outs to SolderSmoke, SPRAT/G-QRP, and Electric Radio magazine. 

Check it out:  https://www.hamradioworkbench.com/podcast/hollow-state-design

Stay to the end for some thermatron-related password management advice from George. 

Thanks to Grayson and to all the folks at HRWB. 

More Info on Tom's Amazing Junkbox 20 meter Receiver (using FPGAs)

 

Back in June we had a post about an amazing junkbox receiver project carried out by Tom in SW England: 

https://soldersmoke.blogspot.com/2021/06/toms-receiver-20-meter-superhet-built.html   

This was a receiver built around SBL-1 mixers and 10.7 MHz filters salvaged from an old satellite receiver.   It was also the first radio receiver project undertaken by Tom.  His use of FPGA technology is especially interesting. 

We asked Tom for more info and he kindly provided it: 

http://soldersmoke.com/tom20receiver.pdf

http://soldersmoke.com/tomRadioschematics.pdf

http://soldersmoke.com/tomFPGAdesign.pdf

Tom also sent me Firmware sourcecode  that may be reusable for STM8 users, and the FPGA design file (for Quartus users). If anyone has a GitHub or similar site that can host these files, please let me know and we will send them to you. 

Mythbuster Video #16 -- GLOWING NUMERALS! In Juliano Blue!

I added two San Jian frequency counters to the front panel. In addition to making the rig a lot easier to operate, they add a classy touch of Juliano Blue to the project.

I got my counters here: https://www.ebay.com/itm/224223678132

There is a limitation of some of the the San Jian counters: https://soldersmoke.blogspot.com/2021/02/a-problem-with-san-jian-plj6-led-counter.html

But this limitation didn't cause any problem with this rig:  In this case I just plugged in the IF frequency of 5.2397 MHz.  I connected the input to my VFO running around 9 MHz.  For 20 meter signals, I select the "up" option;  the San JIan counter just adds the IF frequency to the VFO Frequency.  For example 9 + 5.2397 = 14.2397 MHz .   For 75, I select the "down" option.  Here the San Jian just subtracts the IF frequency from the VFO frequency -- for example 9 - 5.2397 = 3.7603 MHz.  

The band select switch operates relays that select the proper band-pass and low-pass filters.  This switch also alternatively turns on either the 20 meter San Jian or the 75 meter San Jian. 

Mythbuster Video #15 The Mythbuster Signal As Seen in the NA5B WebSDR

Mehmet NA5B has an excellent WedSDR receiver in Washington D.C., about 9 miles east of me. I often use it to check my signal quality. I think this video shows that the 10 pole crystal filter is working and is producing a signal with very sharp drop-off outside the 2.7 kHz passband. You should focus your attention to the passband (yellow vertical lines) near 3895 kHz. That's me.

Once, when I was describing my 40 meter DIGI-TIA to an SDR guy, he seemed surprised that I was using a -- gasp -- crystal filter. "Your skirts must be atrocious!" he said. My HDR sensibilities were deeply offended.

I had hoped that the 10 pole crystal filter would produce skirts so nearly vertical as to make my signal indistinguishable (in the waterfalls) from the SDR signals. At least at this low signal level, it appears to be working.

Mythbuster Video #14 -- ON THE AIR!

On August 5 I put the Mythbuster on the air, making QSOs on both 75 and 20 meters. This video is from the following day -- I was on 75 meters. My first QSO with this rig was on 20 with S57DX. That was a good omen. TRGHS

I had no feedback or spur problems with the BITX40 module amplifier circuit. And I didn't release any IRF510 smoke. There is, of course, a lot more output on 75 than on 20. That's just the nature of the IRF510. I get about 4 watts out on 20 and about 9 watts out on 75 (with a 12 volt supply). At Pete's suggestion I might replace the IRF510 with a Mitsubishi RD06HHF1.

I had a couple of minor problems getting the transmitter going. I will describe these in a future video.

Mythbuster Video #13 -- RF Power Amplifier, and Relay Switching Plan

In this episode we enter into the most fraught part of the construction project: the production of RF power. This is where amplifiers stubbornly turn into oscillators, and where components release magic smoke, or at least burn the fingers of hopeful builders.

I kind of ran out of room when I built the low-pass filters. But, thinking ahead, I wanted to have them on a separate board. And it is good that they ended up in the far corner of the rig.

Just going from one band to two bands adds to the complexity of the rig. I had to add two relays, one to switch the low pass filters, the other to switch the bandpass filters. I ended up with 5 DPDT relays in this transceiver. It was very helpful to have a plan and a diagram for the relays and all the switching.

It looks like each of the three RF amplifier stages provides about 15 db of gain -- about what I need to get to the 5 watt level.

Farhan and the SBITX on Hack-A-Day

 https://hackaday.com/2021/08/06/sbitx-hackable-hf-sdr-for-the-raspberry-pi/

AFTIA! The Audio Frequency Termination Insensitive Amplifier from W7ZOI

 

It really pays to check Wes Hayward's web site.  I looked yesterday and found something that we really need:  A termination insensitive amplifier for audio frequencies -- an AFTIA.  Just last week I was looking at the AF amplifier of my Mythbuster rig, wishing that it had TIA properties.  Now, thanks to Wes, we have a circuit available: http://w7zoi.net/audio-fba.pdf

And let's not forget that it was Wes Hayward W7ZOI and Bob Kopski K3NHI whose 2009 article alerted us to the RF variety of termination insensitive feedback amplifiers. 

Mythbuster Video #12 -- Bandpass Filters

The really cool part comes at the end when I put the scope probe on the output, then on the input of the bandpass filter.  Exciting stuff my friends! 

Mythbuster Video #11 -- Block Diagram and Overview of the Transmitter Circuits

Much of the transmitter is now done. This video looks at the circuitry and how it all fits together.