A Clean Vintage Ham Radio Transmitter: The Collins 32S-3

In an article on IMD and splatter,  tech guru Rob Sherwood noted that the cleanest tranmitter he had ever owened was the Colling 32S-3.   Here is the article.  https://soldersmoke.blogspot.com/2024/09/sherwood-its-time-to-clean-up-our.html

In it, you will see thar Rob has the spectrum anayser two tone test to prove his point.  

This got me wondering:  Why was the Collins transmitter so clean.   Today I looked at some ot the tech info on this rig.  I think I have found the answer. The Collins Collectors Association has a great page on the 32S-3: https://collinsradio.org/cca-collins-historical-archives/the-equipment-of-collins-radio/the-grey-boxes/32s-3/

The key lines are these:  

Click on the paragraphs or go to the link for a clearer view 

I think the explanation of Collins'32S-3 cleanliness is due to 1) Thermatrons in the final stages and 2) Negative feedback to take down any IMD products that might appear due to non-linearities in the finals.   

There is nothing magical in that technique.  Heck, we could homebrew that today.  We could build HDR stations (perhaps transistor-tube hybrids) that would be cleaner than their commercial SDR cousins. 

Ham Radio -- How To Build Stable Oscillators

Spasibo Vasily!  

Wow, thanks a lot Todd.   There is some great wisdom in your video.  You clearly demonstrate that it is possible to build your own stable LC VFOs.  Sure, for many the arrival of the synthesizer chip put an end to this kind of project.  But some of us still want to fully homebrew all the stages in our rigs, and not be dependent on mysterious chips and software written by others.  

I really liked the way Todd acknowedged the tremendous contributions of Wes, and Roy, and Rick and others. 

Of course, all of Todd's recommendations are right on the mark.  I have been following most of them (but I do fall short and occassionally use a Manhattan pad or two).  Todd even gets into the mysterious and arcane practice of boiling (three times!) toroidal transformers.  I do have a preference for air-core coils, but that boiling sounds like fun. 

One thing that Todd and Brad might also want to consider:   tuning linearity.  Too often LC VFOs end up having the frequency spacing very close at one end of the dial and very broad at the other end.  "Bob's Electron Bunker" provides some great tools for alleviating this problem:

https://soldersmoke.blogspot.com/2022/09/the-cure-for-frequency-bunching-up-in.html

Thanks again Todd! 

AG5VG's Homebrew 20 meter Superhet (with a CW rig Coming) (Video)

 Michael AG5VG finished this receiver last weekend.  He hopes to build a CW transmitter using an output of the Si5351.  Obviously I defer to Pete on that one.  Good going Michael.  I think it sounds great and looks even better.  

Vulnerable MOSFETS in NASA's Europa Clipper

 

Oh man, this is terrible.  Just months before launch of the Europa Clipper mission to Jupiter's satellite, they discovered that some of the MOSFETS in the spacecraft might get fried by the Jovian radiation.  1500 MOSFETS.  Ouch.  Details here: 

https://futurism.com/nasa-disastrous-flaw-spacecraft

"QRP Classics" The Book that Got Me Started in Homebrew

https://soldersmoke.blogspot.com/2022/09/fixing-up-old-homebrew-rig-barebones.html

A question this morning from Scott KQ4AOP caused me to Google this old book    On page 59 I found the article about my first transmitter.  Someone has put a copy of the entire book on the interenet.  Here it is: 

https://ham.v4.si/books/QRP%20Classics%20-%20The%20Best%20QRP%20Projects%20from%20QST%20and%20the%20ARRL%20Handbook.pdf

Sherwood: "It's Time to Clean Up our Transmitters"

 

http://nc0b.com/qst-article/NC0B-QST-Nov-2019.pdf

As an analog, HDR, discrete component, radical homebrew fundamentalist, obviously I have been concerned about all the hype about SDR.  SDR advocates often make it sound as if those of us who build with discrete analog components (crystal filters!) are hopless troglodytes, about to be thrown on the ash heap of radio history.  Or something like that.  They sort of imply that without the cleansing benefits of SDR, our signals will remain hoplessly dirty. 

I find it interesting that Sherwood concluded that the cleanest transmitter he ever owned was a Collins 32S-3!  He compared the two tone output of this old rig to that of a modern transceiver.  This was in 2019.  See above.  HDR wins. 

Don't get me wrong.  I want to clean up the signals from my HDR rigs.  But I am encouraged by Sherwood's remarks.  I do not think I will have to go SDR in order to have a clean signal.   I may just  do some two-tone tests on the rigs,  make some adjustments, and maybe build a class A Thermatron .1 kW linear. 

IMD in Transmitters -- Splatter? Or Signal Strength?

https://www.newsvhf.com/conf2024/PresPapers/WA1MBA-IMD_in_Transmitters.pdf

Here is a good (and very recent) article on IMD ("splatter") produced in transmitters. The focus is on VHF, but much of this is relevant to HF operators.  I found the footnotes on the ARRL "Clean Signal Initiative" to be worrisome.  They seem to just be assuming that all ham operators will be using commercial gear, and the "OEM" needs to be made to meet certain standards. This seems to leave the homebrewer out in the cold.  I can see where someday soon, the "standards" will exceed the capability of analog homebrewers.  That would be bad.  

The role that signal strength plays in the perception of "splatter" is often misunderstood by the "waterfall police."  We often we hear some irate waterfall policeman screaming that,  "You are 40 over and far too wide."   Here is a good quote from the article on this point: 

"If you have a calibrated spectrum display (as many SDR’s are these days), you can directly measure the level difference in dB. If it is 30 dB or more, then it could be an acceptably “clean signal”, even if it is bothersome. Most ham voice communication is conducted with less than 30 dB signal/noise, and in that case the unwanted IMD is buried in the noise."

And even in a low noise environment,  if the signal is 40 db over S9. that would mean the signal PEP is at -33dbm.  If the IMD products are 46 db down from the signal peak, that means your IMD products are -79 dbm.  That is S-8!   That signal will look quite wide in the waterfall, but it would be within FCC specs, right? The problem here is not so much distortion, as signal strength.  And let's remember that "legal limit" is usually a misnomer:  FCC regs require hams to use the minimum power necessary, not 1.5 kW on every single QSO. 

The Surprising Difficulty of Analog Circuit Chip Design -- AI to the Rescue?

https://www.youtube.com/watch?v=lNypq1XuZRo

Really interesting.  Why the design of the analog portions of chips is so much harder than the design of the digital portions.  

Great channel. 

Sony and the Transistor

 https://www.youtube.com/watch?v=7pi9k5n7Wrw

I found the comment about Sony's belief that NPN transistors are superior to PNP very interesting. 

IMD and Splatter

 

https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/hr/1988/10/page71/index.html

I think the point I was trying to make about the influence of signal strength is here:  

Referring to fig. 1C, note the high level of rf at the 3rd order level - typically 36-dB down. Consequently, there will be rf energy outside the normal 23 kHz passband that will be only 36-dB below the carrier peaks, or about one four-thousandth of the peak power. Not bad if the station is only 25-30 dB out of the noise, but very objectionable if it's 40-60 dB out of the noise.

I think it is supposed to read "2-3 kHz passband" vice "23kHz passband."

I guess the point is that QRP levels of operation can hide a host of ills.   IMD ills.  This makes me wonder about the cleanliness of my own signals.   I will have to do some more careful measurements. 

Ham Radio in the 1970s (and earlier, with some cool Jazz). What favorite rigs do you see?

Rogier PA1ZZ sent me this today.  I think I may have seen pieces of it before, but this restoration 

is really nice.  But ham radio seems to have been a lot cooler in California.  I don't remember it being so socially advantageous on the East Coast.   See Dilbert cartoon below. 

So many memories: 

-- The video opens with someone working on a QF-1 Q multipliers.  We have destroyed so many of these relics, in pursuit of the variable capacitors (which turn out to be not so good). 

-- A Drake 2-B on Field Day. 

-- An HT-37 in a shack.

--What looks like an HW-32a in a mobile rig. 

-- Maybe an HW-101. 

--  A BC-348. 

-- The ATV station with lots of homebrew gear was very cool. 

-- I also liked the single THERMATRON homebrew CW rig made from an old TV.  FB. 

-- The CW used in the video was all pretty good.  There was a lot of chirp.  This, of course, adds character to a signal.  FB.

After the video, they take a walk down memory lane, looking at ham radio magazines with some cool jazz playing in the background.  I saw a Swan 240 and a D-104.  The debauchery of the 1970s was evident on the magazine covers.  Even QST seemed to be caught up in this.  Check out the August 1975 cover of QST.  

Anyway, this video was a lot of fun.  Thanks Rogier!  

What favorite rigs do you see?   Make note of them in the comments. 

This video and the Dilbert cartoon reminded me of a discussion we had many years ago about THE KNACK: 

https://soldersmoke.blogspot.com/2008/11/cry-for-help-soldersmoke-responds.html

Excellent New Video from Grayson KJ7UM on his Thermatron version of the Michigan Mighty Mite

Here is a really wonderful video from Grayson Evans, KJ7UM, author of Hollow-State Design for the Radio Amateur.  

I really loved this video.  Throughout we see Grayson's sense of humor.  Early on he explains the differences between a tube (what remains from a roll of paper towell), a valve (like the plumbers use) and a THERMATRON (like a 6146).  Grayson is the inventor of the word Thermatron.  We should all pledge to use it whenever possible. 

Grayson's humor also shows up when describing the parts acquistion process for the Thermatron Michigan Mighty Mite.  He puls out a coil (a huge coil) and laments that it is not -- despite its large size -- sufficiently inductive. 

There are wonderful shout outs to SolderSmoke, to Electric Radio, to the Color Burst Liberation Army, to Pete Juliano,  and to Rex Harper.  

Grayson describes the utility of Rex Harper's Thermatron ME pads.  

During the video, Grayson actually builds the Thermatron MMM.  In under 2 minutes!  He then experiences the Joy Of Oscillation, or JOO as it has come to be known.  OM needs a contact -- listen for him on 3579.  He is calling CQ.  

Grayson talks about his book, Hollow-State Design.  I have a copy with me here at SolderSmoke Shack South in the Dominican Republic.  Great stuff.   The above link takes you to Lulu, where you can order the book.  You can also get it from Electric Radio Magazine here: https://www.ermag.com/product-category/books/

Thank you Grayson for bringing us this video, and so much more over the years.  And for giving us the very useful and fun word:  THERMATRON!