A Tale of Two Old Analog VFOs -- Artificial Intelligence's Role. PLEASE COMMENT!

The Kenwood VFO under test, with 2 Yaesu VFOs Standing By 

I have sung the praises of the VFOs taken out of the old Yaesu FT-101s.  I am using them in two homebrew 20 meter SSB transcievers,  one in the Dominican Republic, the other here in Virginia.  We started buying these things just for the anti-backlash reduction drives. But the vendors would send along the reduction drives AND the entire VFO module.  These circuits were all analog, and all discrete component.  I understood them, and had completely homebrewed circuits very much like them.  So I felt comfortable using them. 

Somewhere along the line, I got the VFO from a Kenwood TS-820s.  My motivation was the same:  I wanted the anti-backlash reduction drive. But as with the Yaesus, the entire VFO box came with the purchase.    The frequency on this one was much lower than the Yaesu.  the Kenwood ran from 5-5.5 MHz, the Yeasu was up around 9 MHz.  On this alone, the Kenwood seemed better.  

I recently put the Kenwood on the bench and began testing it.  I used Artificial Intelligence (AI) in the tests.  The results were good and bad.  Sometimes AI helped, sometimes it made matters worse.  Mike WU2D recently used AI to look at the tubes of an old receiver he was working on.  He too was impressed by the usefullness of AI, but I think he too had some misgivings. Here are some of Mike's conclusions: 

Let's start with a fundamental question:  I asked Gemini which of the two "ages better."  Gemini said that the Kenwood was superior in this regard.  I disagree.  Here is why: 

-- Tuning on the Kenwood was very jumpy and very scratchy.  AI correctly said that this was probably due to corrosion over the years on the connections between the main tuning capacitor and ground.  Strike 1! AI recomended cleaning with DeOxit. As a last resort they recommended putting some solder wick between the rotator shaft and ground.  I did that and it fixed the problem (you can see the solder wick in the picture above), but I never had to do that with the Yaesu VFOs.   

-- The schematic of the VFO shows a .9 V RMS output from the VFO.  But it does not specify a 50 ohm load.  Here is the Yaesu schematic: 

AI kept insisting that I use a 50 ohm load.  When I did, the output was reduced down to 54 m V rms. I questioned AI about the load, but it kept insisting on 50 ohms.  Only later, did AI point out that in the Yaesu, the VFO would feed into a HIGH IMPEDANCE load.  Strike 2. 

-- Gemini kept warning about the Q3 and Q4 transistors. They were 2SC460 transistors with weird (ECB) pinouts.  And they were prone, it said, to a horrible sounding disease: "Original Hitachi 2SC460 transistors are infamous in vintage ham gear for silver migration ("black foot disease"), where the lead plating oxidizes, turns black, and causes severe noise, leakage, or intermittent oscillation failure." AI happily recommended replacing them with 2N3904s.  I did this, but the voltage on the emitter was way off.  AI blamed this on the new transistors (that it had recommended!) saying that their hfe was too high (so, uh, why did you recommend them?).  It then said that the direct coupling from Q3 to Q4  was at fault;  it recommented putting a .001 uF cap between these two transistors, along with two resistors for the biasing of Q4.  I did this.  I am not sure if it was necessary.  Strike 3. 

-- Gemini said I should check D3. It was germanium, you see, and "notorious"  for going open.  It was open.  I replaced it with a wire, but AI had a fit.  It worried that voltage from the follow-on circuits in the Kenwood would mess up the voltages on Q4.  I told AI not to worry about this -- all I had was the VFO!  Strike 4. 

-- I still wasn't getting good output.  Here AI was very useful.  First it told me to check the voltage on the emitter of Q4.  It was too high.  Then it told me to look at the resistance to ground from the emitter of Q4.  Uh oh.  It was open.  I quicky went through the connections to ground.  L6 was open.  I relaced it with 100 uH inductor. This corrected the situation.  I now had 1 volts AC rms at the output with no load and .8 V AC rms with a 1000 ohm resistor in the load.  SCORE ONE FOR AI. 

So, looking back, I came to several conclusions:  

-- Gemini was just wrong in saying that the Kenwood VFO ages better than the Yeasu VFO.  The Kenwood had Germanium diodes, weird transistors that get "Black Foot" disease, main tuning caps that get scratchy due to corrosion, inductors that go open.  Yuck.

-- You have to take the recommendations from AI with a grain of salt (see WU2D's conclusions above).  Sometimes they are right, sometimes they are wrong, and sometimes they recommend things that might not be necessary.  Dean KK4DAS points out that AI's seem to do better when you upload the schematic.  Maybe this lets AI analyse it using a simulator.  I had not done this.

-- I will probably use the Kenwood VFO in a 17 meter SSB transceiver.  I recently bought some 13 MHz crystals for the filter and the BFO/Carrier Oscillator from Mouser.  And AI confirms that this combination should not produce any problematic spurs.  We'll see.  The ultimate test is still real-world construction. 

What do you guys think about using AI in projects like this?  Will AI improve? 

Does a simple, single diode envelope detector function the same way as a product detector does?

Mike WU2D has an interesting series of videos on the simple detectors used in crystal radios.  Mike's videos touch on a discussion that I had a few years ago with a member of the Vienna Wireless Association.  I was describing how an envelope detector uses rectification to recover (demodulate) the audio from an AM signal.  The club member dismissed this explanation and claimed that what really happens is that the diode simply mixes the carrier and the sidebands to produce audio.  He claimed that the rectification "theory" was just a fable created to deal with people who really didn't know how mixers worked.  See:   https://soldersmoke.blogspot.com/2022/12/is-envelope-detection-fable-or-is-it.html

I was kind of disappointed by Mike's videos.  He seemed to take an agonostic position on this issue.  He framed it as "some people believe in the rectification explanation, and some people believe in the product detection explanation." As if both explanations are equally valid.  They are not. 

This morning, I asked AI about the two explanations.  Here is what AI says: 

 Does a simple, single diode envelope detector function the same way as a product detector does? 

AI Overview

No, a single diode envelope detector does not function the same way as a product detector because the envelope detector is a non-linear circuit that recovers the audio from a full amplitude-modulated (AM) signal by following its envelope, while a product detector is a linear mixer that recovers the audio from various modulated signals (including DSB-SC and SSB) by multiplying the modulated signal with a local oscillator. Product detectors are more versatile and offer better signal quality than simple envelope detectors, which are limited to demodulating DSB-AM signals with a full carrier. 

I know that AI sometimes gets it wrong, but I think that on this one, it has it right. 

I don't think it is necessary to include discussion of modulation percentages nor diode biasing to clearly explain what is going on. 

Even if you are using a very weak signal and are completely in the square law region of the characteristic curve,  you are still essentially dealing with a form of rectification:  portions of the signal on the positive side of the curve will experience less attenuation than signals on the negative portion of the input curve.

When we use a crystal receiver, we are relying on the rectification done by the diode -- even if the rectification happens in the square law region.  After the crystal there is some low pass filtering.  The envelope of the AM signal remains and this is the audio signal that we listen to.  That is why we call it -- correctly -- an envelope detector.   And as the AI says, an envelope detector funcions differently than a product detector. 

A Tale of Woe from Mike WU2D, PLUS: The Importance of Band Noise

It was so cool to watch master homebrewer Mike WU2D candidly describe his error (tale of woe) made while building the Simple X Super receiver.  

It was also great to see his joy in hearing the band noise.  Watch his glee as the noise jumps up when he connects the antenna.  "That's the good stuff!"  Indeed it is.  So many younger builders see noise -- all noise -- as a bug not a feature.  Mike obviously sees it as a feature:  Thunderstorms in Brazil!  The weed-whacker down the street!  Remants of the Big Bang!  Hearing this stuff lets us know that the machine we have built is alive, and is inhaling the universe.  

Thanks Mike. https://www.youtube.com/watch?v=T_Mz9HljCys

 

No Bunching Up! It is Possible to Achieve Dial Linearity (and Stability) with an LC VFO

One of the major complaints about LC VFOs is that they allegedly cause "non-linear tuning."  Essentially, this complaint claims that you will inevitably end up with your frequencies all "bunched up" at one end of the tuning range, with frequencies greatly "spread out" at the other end. BUT WE HAVE FOUND THAT THIS IS NOT NECESARILY TRUE.  With a bit of careful design work, you can avoid the dreaded "bunching up."  I have used the calculator in Bob's Electron Bunker to DESIGN VFOs that do not "bunch up" the frequencies.  

Recently, Mike WU2D built a version of the Simple X Super receiver.  It has a VFO in the 5 - 6 MHz range.  And guess what?  There is NO bunching up of frequencies. As proof, I present the tuning dial that Mike made for his completed receiver.  See above.  Note the nice linear tuning.   

So you see, success in this area is possible -- all it takes is some careful design work. 

Similar results are possible with the other major allegation about LC VFOs:  That they are inherently and irreparbly unstable.  Proponents of this theory would have you believe that only by the use of an Si5351 (or something similarly digital) is stability possible.  Again, NOT TRUE!  It is possible to make LC oscillators that are stable.  All it takes is careful design and good construction practices. 

Mike WU2D's Video on the SimpleX Super Receiver -- Part II

 Another FB video from Mike WU2D.   

But you know,  I too find myself kind of opposed to front panel on-off switches.  I power my rigs with small DC supplies.  I just turn on the supply when I want to use one of the rigs.  I don't have or need a switch on the front panel of the rig.  

I especially liked Mike's use of the gate dip meter and, of course, the Q meter.  FB OM. 

I must say I have a preference for the first version, but only because I dislike the regenerative circuit in the second version.  I do like the newer-style coils -- I have one in the BFO of the Mate for the Mighty Midget receiver.   

Thanks Mike for the sideband inversion factoid in Part 1!   The Hallas Rule -- words to live by. 

One word of caution.  I used 6U8s on my Mate for the Mighty Midget receiver.  I had good results, but WA9WFA had a lot of trouble.  We eventually concluded that the 6U8s didn't age well.  And they were quite long in the tooth.  We found (from the tube guys) that 6EA8s aged better and were a good and easy sub for the venerable (perhaps TOO venerable) 6U8s.  I switched tubes in my rig and it did seem to work better.  BTW, this is the receiver that I use to listen to the Old Military Radio Net on Saturday mornings.  

Here is the story of our switch from 6U8s to 6EA8s: 

https://soldersmoke.blogspot.com/2022/02/6ea8s-in-mate-for-mighty-midget-and.html

SimpleX Super Superhet Receiver -- A Great Video from Mike WU2D

Here is another great video (and project) from Mike WU2D.  I'm a big fan of homebrew superhets.  And wow, Mike presents a band-imaging superhet!  Two bands for (almost) the price of one!  I have FIVE homebrew dual-band band-imaging transceivers around me.  Believe me, once you have the experience needed to build an SSB transceiver, a dual-bander is the way to go.  Five bands seems like a bit too much.  But two seems to be at the sweet spot.  

I wrote to Mike reminding him to talk about the sideband inversion problem.  This rig will invert the 75 meter signals,  but this is easily resolved by just shifting the BFO frequency.  I also pointed out that many of today's builders will be detered by the need to scrounge for parts.  Where oh where is the BOM OM? 

Thanks Mike! 

Mike WU2D Does a CCC Camp POTA with 1930's Gear

FB Mike.  CW without sidetone is not for the faint of heart.  

Walter KA4KXX saw Mike on the Reverse Beacon Network. 

Mike's QSO with KN4RRQ was especially interesting.  Tom was running a 1929 breadboard-style transmitter: https://www.qrz.com/db/KN4RRQ 

Mike WU2D POTA CCC Camp Activation (21 October 2024) with 1930s-era Station -- See If You Can Contact Mike!

Frank Jones lives!  See if you can work Mike on Monday.  Let us know if you do! 

--------------------------------

Bill,

 

I’m scheduled to tour the Civilian Conservation Corps. Camp at Bear Brook State Park here in NH on Monday. This is the largest totally intact camp in the country.

I will be activating POTA with the 1930s portable Station. The POTA CCC Camp event is scheduled for Monday around 2:30 ET (if I get everything setup after the camp tour). Primary 7057 kHz Sec 7054 kHz.

 

The station is an internal battery powered, push-pull Jones Oscillator Transmitter at around 3 Watts out, and a two-tube regenerative receiver that is a period ham artifact. So, four type 30 battery tubes in total.

The antenna is a single wire feed Windom with suspended counterpoise so basically an Off Center Fed Hertz (OCFH).

 

Between the weather, running the station, logging, and doing camera work, and of course, MURPHY - this should be nuts.

1930s Regen with Transmitter – Fully Self-Contained Portable. Note Charger that is attached to top off the internal battery on transmitter. I did not buy the proscribed 25 9V Batteries and make a TX HV pack up! I used a DC-DC converter and a LiPO drone battery! The Receiver is 100% Dry Cells However.

 

73’s Mike WU2D

----------------------------

More info here: https://www.youtube.com/watch?v=N2Pdprx0ItY

And many other great videos on Mike's YouTube channel: https://www.youtube.com/@MIKROWAVE1

A Paraset and the Heathkit SG-6 Signal Generator (Video)

Mike WU2D put out this nice video (above) about whether or not he should part out his Heath SG-6 signal generator, using the parts in a Paraset construction project.  I faced a similar question years ago: 

https://soldersmoke.blogspot.com/search?q=SG-6

I just solid stated the SG-6.  I was influenced by Farhan and the drinking straws that he picked up with his kids at a McDonalds in Hyderabad. 

As with the QF-1, I say to Mike: GO FOR IT OM!  You need those parts for other projects.  Don't feel bad about the SG-6.  But keep that switched coil assembly -- it is quite useful. 

Electronic Toys and Their Influence on Us

Mike WU2D recently put out this interesting video.  I vaguely remember the springs on the Radio Shack kits -- I also remember (bitterly) not being able to get their shortwave receiver to work.   I really wanted to tune in HCJB and Radio Moscow.  This probably led me to ask Santa for a Lafayette HA-600A receiver in 1973 or so. 

An earlier influence was the little intercom kits.  I think they worked over the AC lines?   We took some of them to the beach bungalows we had in Lavallette NJ.  With them we were able to speak clearly to similar units in nearby bunalows.  Wow, that was cool. That got me interested in radio. 

Cassette tape recorders were another early influence. I still have a recording I made with a tape recorder I got for Christmas, probably in 1972.  I used this recorder to practice CW for the ham exam. 

I managed to escape the CB madness.   But I came close to falling into the groovy psycho stuff of the early 1970s.  I remember the Transcendental Meditation gizmos.  I never built one, but if I had I may have been better off with CB. 

I kind of wish I had followed the example of the Woz and Jobs by making telephone blue boxes.  This could have led me to riches.  But as Jean Shepherd used to say, young men often come to a fork in the road: one path leads to wealth, the other to ham radio flea markets.  I got on the second path.  

Thanks Mike! 

 

A Contact with my Old Azorean DSB Transceiver

I've been thinking about balanced modulators, and I wanted to see how some of my early circuits performed.  So I pulled this OLD Double Sideband rig off the shelf and fired it up. The balanced modulator -- and everything else! - worked fine,  and I soon made contact on 17 meter SSB with Gene, AB9GK. 

This was the first DSB transceiver that I ever built.  I made this out in the Azores, probably in 2000 or 2001.  Years later I had replaced the RF power amplifier with a "JBOT" (Just a Bunch of Transistors) designed by Farhan.  

Over on my YouTube channel a comment came in from my friend Jack:  

@dhakajack

"Looking inside and seeing the o-scope probe in place while the radio was on the air reminded me of neurosurgery where the patient is awake and talking while the surgeon probes different brain regions soliciting feedback. Sure, ham radio isn't neurosurgery, but it's not too far at times. Also, you already have rocket science covered."

Here is an article about my build of that first rig:

https://www.gadgeteer.us/17METER.HTM

I think the article captures well the trials and tribulations faced by new homebrewers, perhaps with the twist that comes from being out in the middle of the Atlantic ocean.  

Mike WU2D is having similar fun with his homebrew 10 meter DSB transceiver: 

https://www.youtube.com/watch?v=uZt1LTGyoHc

I was struck by how similar Mike's early QSO experiences were with mine.  We both put our DSB transmitters on the air before they made their way into real cabinets or boxes. 

Here's mine from 2001 in the Azores: 

Retro QRP Rigs of the 1960's, 70's, and 80's -- Video by Mike WU2D

It is time to put aside (again!) all of the heated ideological arguments about the power level that defines "low power."  Just sit back and enjoy this wonderful trip down QRP memory lane. 

Mike's description of the simple, single-transistor QRP transmitter was really nice.   I recently made something similar: https://soldersmoke.blogspot.com/2023/02/first-qso-with-high-school-receiver-100.html  And Mike does a nice plug for our beloved Michigan Mighty Mite.  Go CBLA! 

The modular idea:  words to live by my friends. 

40673!  TT2!  And G3RJV's PW Severn - indeed, bow your heads!

Wow, the Ten Tec Power Mite (or Might!) -- I still want one.  Same for the Argonaut -- what a great name (sounds like a "magic carpet), and with SSB to boot!  I want to join the Argonaut cult! 

I have both the HW-7 and HW-8 (the HW-8 is heading to the Dominican Republic).  This video makes me want to fire up the HW-7.  Maybe on 40.  

My 40 meter homebrew rig (Digi-Tia) has in it the filter from that old Yaesu FT-7 rig.  The filter was given to me by Steve "Snort Rosin" Smith.  https://soldersmoke.blogspot.com/2015/05/bitx-digi-tia-build-update-2-installing.html  

Thanks to Mike for including me in the credit roll at the end.  What a great group of people -- it is a real honor to be listed with those folks.