Using the RF Power Amplifier of the BITX40 Module

 

PA shematic from the BITX 40 Module

Click on the diagram for a better view

C.F. Rockey W9SCH (who alerted us in SPRAT 22 to the chicken sacrifice option) spoke of transistors that exhibit "quantum mechanical necromancy."  Rockey explained that when this happens, "The transistor simply turns up its toes and dies. Not even an Atomic Physicist can tell you why!"  

This often (very often!) happens with homebrew power amplifiers.  So when we find a good one, many of us stick with it, using the same power amp circuit in rig after rig.  I have done this with the power amplifier from the BITX40 Module. 

Mythbuster (75 & 20 Meter) version (early)  

Click on image for a better view. 

https://soldersmoke.blogspot.com/2021/08/mythbuster-video-13-rf-power-amplifier.html

Same amplifier built into Version 2 of the 15-10 Transceiver 

Click on image for a better view. 

In the build for the 15-10 transceiver you can see some changes.  I used an RD06HHF1 instead of an IRF-510.  I used an 8.1 volt zener diode instead of the regulator chip. I set the bias at around 5.5 volts DC on the gate of the RD06.   I used a smaller, metal can driver transistor (it works fine). I changed the input/output physical configuration between the pre-driver and the driver stages (I think it was kind of goofy the way I had it in the Mythbuster).  Finally, you can see how I used a small piece of copper tape (with conductive adhesive) to shield the line going from the driver transformer to the gate of the RD06.  The wire was too small to use a bit of shielded coax, but I think the copper tape and the copper clad board beneath it work just as well. 

Farhan provided me with some fascinating background on this circuit: 

Bill,

I just saw your post on the bitx40 power amp. The credit must go to Wes for this, it is from the Lichen transceiver described in 6.9 of the EMRFD. I merely copied it with some modifications for it to work with junkbox components.

It bears mentioning that at that time I didn't have a way of generating two tone signal or measuring the IMDR. Those came later when I built my own spectrum analyzer based on Wes and Terry White's spectrum analyzer. It was sheer luck that I picked this power chain that already had careful gain distribution.

For the output, the original build used and LPF with inductors wound on a ballpen shell and TV baluns cores instead of toroids. Again, it was incredibly lucky that they worked at all. 

- f

"Dream It - Make It" -- Rich WB4TLM, Mrs. Filoramo, and C.F. Rockey W9SCH (aka The Rock)

 

Rich WB4TLM spotted my bog posts about famed QRPer C.F. Rockey W9SCH.  He followed up by sending me a link to the WB4TLM blog.   It is a lot of fun.  It describes his troubles in school and his subsequent participation in The Rock's electronics class. 

Rich's blog has some great inspirational quotes for ham radio homebrewers.  He is now teaching at Full Sail University. Their fabrication lab has a motto: "Dream it -- Make it."  And in a quote that made me think of my good friend Pete Juliano, Rich tells his internet-jaded students, "I've been there...done that... I can get you there faster." FB OM.  

Here is the link to Rich's blog:  http://richardarndt.com/about

Thanks Rich.  And thanks to Mrs. Filoramo and The Rock! 

Rich WB4TLM

From a Student of C.F. Rockey, W9SCH

C.F. Rockey W9SCH

We have discussed the monumental work of C.F. Rockey, W9SCH, SK before.  Yesterday a comment appeared under that post that is just too good to leave buried in the comments.  It appears below.   Jeff's comment also caused me to dig up my small collection of "The Five-Watter" issues from the Michigan QRP Club.  Rockey wrote a column for that magazine.  It contains a lot of tribal knowledge.  Here is Jeff's look back:  


This turned up for me in a Google search for "Charles Rockey QRP ARRL" during a phone call with a friend of mine who was bemoaning that he never got a novice license because he could not master Morse code (he is in his mid-60s, as am I). I was taken back to the communications electronics class I had my freshman year at New Trier East in Winnetka (not Wilmette) IL in 1971. That class was taught by none other than C.F. Rockey, known to us students as The Rock. I think about him fairly often because I grew up to become a very hands-on engineer and can recall parts of his class quite clearly, even at this remove. Somewhere I still have the reports we had to write (typed on a typewriter) each week. He was a huge influence on me and I was saddened to have his passing undeniably confirmed for me. I have the little chemistry book he authored beside me now *Electrons, Atoms and The World* and am glad to be able to read his obit. One thing needs to be added to it: He won the ARRL 5000 mile-per-watt award for working Anzio, Italy from his home north of Chicago on 5W. I am very lucky to have had him as a teacher and mentor for those years. Thanks for sharing. Cheers, Jeff Mizener, DFW-TX