Improving the Product Detector in the Lafayette HA-600A

Diode product detector on the left, BFO amp in the right

As noted in an earlier blog post, I didn't like the sound of SSB and CW when using the product detector in my Lafayette HA-600A.  It just did not sound right.  The receiver sounded fine on AM with the diode detector.  But when I switched in the product detector, it sounded bad.  The BFO was fine.  The problem was there even when I used an external BFO.  And SSB sounded great when I just coupled some BFO energy into the IF chain and used the diode detector to listen to SSB.  My suspicions were focusing on the very simple BJT product detector. 

Steve N8NM built the HA-600A product detector both in LTSpice and in the real world.  It worked fine in both versions.  Steve even put the product detector into his S-38 receiver -- he reported it worked well there.  

I too built the thing in LTSpice.  Then I went and rebuilt the circuit on a piece of PC board.  I connected the new circuit to the HA-600A, using my external FeelTech sig generator as the BFO.  IT STILL SOUNDED BAD ON SSB.  

At this point I started Googling through the literature.  I found a promising article by Robert Sherwood in December 1977 issue of Ham Radio magazine entitled "Present Day Receivers -- Problems and Cures." Sherwood wrote: 

"Another area that could use additional work is the product detector.  As the name implies, its output should be the product of the two input signals. If BFO injection is removed, output should go to zero. If this is not the case, as in the Heath HW series, envelope detection is also occurring, which causes audio distortion." 

I checked my circuit.  When I removed the BFO signal from the product detector, envelope detection continued.  In fact, with the receiver in SSB mode, and with the BFO disconnected, I could listen to the music of WRMI shortwave.  It seemed that Sherwood was explaining well the problem I was having: Simultaneous envelope and product detection was making SSB sound very bad in my receiver.   What I was hearing just seemed to SOUND like what you'd get with a mixture of product and envelope detection: "scratchy" sounding SSB.  This also seemed to explain why SSB would sound fine when using the diode detector with loosely coupled BFO energy -- in that case it would be envelope detection only, with no ugly mixture of both kinds of detection.

So I built a better detector.  I had had great luck with the two diode one trifilar transformer singly balanced design used by both Doug DeMaw and Ashhar Farhan. I built the circuit using one of the trifilar toroids given to me by Farhan, and connected it in place of the original BJT product detector.  With the FeelTech Sig Gen as BFO, I got good results -- most of the signal disappeared with I disconnected the BFO.  Looking at the circuit, I realized that I was balancing out not the IF signal but instead the BFO signal.  To minimize envelope detection I needed to put the IF signal on the balanced input of the product detector (to L1 in the diagram above).  When I did this, envelope detection seemed to disappear completely and the receiver went silent when I disconnected the BFO.  

Finally, I needed to find a way to use the BFO in the HA-600A with the new product detector.  Obviously I needed more BFO signal -- I needed about 7 dbm, enough to turn on the diodes.  I converted the outboard product detector board into a simple amplifier and put it between the HA-600A BFO and the BFO input port of the new product detector.   This works fine. 

A few issues remain: 

1) The output from the HA-600A BFO through the above BFO amp (and across the 50 ohm resistor) is NOT a pretty 455 kc sine wave.  But the peaks of the distorted wave appear to be enough to turn on the diodes, and when I look at the voltages across each diode (on my two channel 'scope) I see mirror images -- one is on when the other is off.   Is this good enough? 

2) Moving the BFO input from L1 to the junction of the two 50 ohm resistors (that is actually a 100 ohm pot) has big implications for how this mixer works.  With the BFO energy going through the toroid, BOTH diodes are being alternately turned on and turned off.  But both are on, and then BOTH are off.  With the BFO energy going in through the other side, one diode turns on when the other is off.  I think the mixing result is the same, with AF coming out of the output port, but the way the mixer works in this configuration is very different. Does this sound right? 

HA-600A Gets a New Coat of Paint -- After Almost 50 years!

 

The HA-600A that I picked up last week was looking kind of sorry.  There was a lot of rust on the cabinet.  Below is the before picture. 

I'm not really into cabinetry or radio aesthetics, but it is amazing what a 6 dollar can of spray paint can do. Formula 409 also helps. I moved the light bulbs forward a bit to get more light on that Juliano Blue dial. 

I am really enjoying this radio.  It has brought back many memories.  I think I got one for Christmas in 1972.  I was 14.  I got my Novice ticket on April 27, 1973 and made my first contact on July 19, 1973.  For that first contact I was using an HA-600A and a Heathkit DX-40.  Later I used the Lafayette with a Heathkit DX-100.   The HA-600A was replaced by the far superior Drake 2B on April 11, 1974.  So I used this receiver for more than two years.  

Looking around inside this receiver (and following up with Google) I learned some more about it: 

-- It was made in Japan. 

-- The manual says it has a "mechanical filter" but in fact it has a Toyo ceramic filter.  This may have been just an honest mistake by the folks who wrote the manual -- maybe they didn't understand the difference between the two types of filters. 

-- There is a big difference between the HA-600 and the HA-600A, mostly in the front end circuitry.  The HA-600 has fewer amplifier circuits at the front end.  This probably explains why the HA-600 I picked up did not seem to live up to my memories of my teen-year HA-600A.  

The fellow who gave it to me tells me that it had belonged to the short-wave listener father of a friend of his. 

I know we have a lot of tube-type receivers that are much older than this thing, but I still think it is pretty amazing that this is a receiver that I used almost half a century ago.  And it is still as good as new.

TRGHS -- My First SW Receiver Offered FREE for Pickup -- The Lafayette HA-600A (Looking for Globe VFO Deluxe)

 

So on September 27,2020,  I was sitting quietly in my shack, perusing the postings on various radio-related Facebook groups, when suddenly I saw it:  my very first shortwave receiver, the magic box that had put me firmly on the path to amateur radio, the Lafayette HA-600A.  Joe, the owner,  was offering it FREE to anyone willing to pick it up at his home in Virginia's Shenandoah Valley.  Holy Cow!  I was scheduled to drive through that very valley later that week.  A message was sent and the deal was done.  CLEARLY THE RADIO GODS HAD SPOKEN (TRGHS).  

Sure, the cabinet looked a bit rough, but I had high hopes for this receiver.  A while back I had -- in a similar fit of nostalgia -- bought what had been advertised as a Lafayette HA-600A on e-bay.  But it turned out to be a Lafayette HA-600 (no A).  I immediately noticed a big difference in performance.  That was NOT the radio that I remembered, not the receiver that had carried HCJB and Radio Moscow to me. Joe was clearly offering the A model.  

A few days later I was in Joe's front yard for the hand-off, and a few days after that the HA-600A was on my bench.  

I quickly realized how little I knew about this receiver.  Mine was a Christmas gift, probably in 1973. (A few days ago I talked to my mom and thanked her for driving all the way to New Jersey to get this receiver for me.)   I was so taken with this thing that I feared doing something -- anything -- that might mess it up.  I lived in fear, for example, that some sort of freak mid-winter lightning bolt might destroy it.  I covered it with a towel each night lest dust encumber its "jeweled movements." Obviously I was just not inclined to crack open the case and have a look around. So I didn't, and the receiver remained pretty much an appliance for all the time I owned it.  (I eventually sold it on consignment at Electronics 59 in Spring Valley, New York.  The proceeds probably went toward the purchase of a much better Drake 2-B receiver.) 

I downloaded the manual and familiarized myself with the receiver:  It is a single conversion superhet with a 455 kc IF.  It is all solid state with no ICs -- all discrete transistors and diodes. The manual claims it has a mechanical filter.  I kind of hoped for something like a Kokusai mechanical filter,  but it turns out that the filter was really ceramic, not mechanical.  Bummer.  

The thing fired up right away and was inhaling on the correct frequencies.  I noticed immediately that (as Joe had indicated) some of the controls were scratchy.  I also noticed that the ganged band selection switch was intermittent and required some jiggling to get it to work properly.  A few squirts of Deoxit D5 took care of all that. There seemed to be a bit of dirt in the main tuning capacitor, but I think I managed to blow that out using a can of Dust-off.    I was quickly listening to the SW broadcast stations, and to radio amateurs on 75 and 40 meters. 

Out of curiosity, I compared schematics of the HA-600 and the HA-600A.  There was indeed a big difference -- the front end of the 600 lacks a lot of the RFA amplification circuitry of the A model.  That's probably why is seemed so deaf and so different from what I remembered of the A model. 

There is really not a lot to do on this receiver.  I'll get some paint to fix up the top cover.  I may check the alignment.   But this single conversion receiver is so simple that alignment would be quite easy.  In many ways this receiver seems like a solid state analog to the Hammarlund HQ-100, but without the clock, and without the regeneration circuitry.   The dial lacks the exotic station locations (Java!) that make many of the older receivers so much fun.  I guess this is an indication that this receiver was aimed more at amateur radio operators than at shortwave listeners ( I was both).  I wonder how the ham band-only HA-800 compares to the HA-600A? 

I could pair this receiver up with a DX-40 transmitter that I have on the shelf and I'd be most of the way toward re-creating my novice station.  Anyone have a Globe VFO Deluxe?   That would complete the setup.  

Thanks very much to shortwave listener Joe Pechie for providing what is, for me, a very meaningful piece of gear. 

Here's a short video on the receiver: 

 

Wrapping up the HA-600A Product Detector Project -- Let's Call Them "Crossed Diode Mixers" NOT "Diode Rings"

This has been a lot of fun and very educational.   The problem I discovered in the Lafayette HA-600A product detector caused me to take a new look at how diode detectors really work.  It also spurred me to make more use of LTSpice.  

In the end, I went with a diode ring mixer. Part of this decision was just my amazement at how four diodes and a couple of transformers can manage to multiply an incoming signal by 1 and -1, and how this multiplication allows us to pull audio out of the mess. 

But another part of the decision was port isolation: the diode ring mixer with four diodes and two transformers does keep the BFO signal from making its way back to into the IF chain.  This helps prevent the BFO signal from activating the AGC circuitry, and from messing up the S-meter readings. LTSpice helped me confirm that this improvement was happening:  in LTSpice I could look at how much BFO energy was making its way back to the IF input port on the diode ring mixer.  LTSpice predicted very little, and this was confirmed in the real world circuit. (I will do another post on port isolation in simpler, singly balanced diode mixers.)  

At first I did have to overcome some problems with the diode ring circuit.  Mine seemed to perform poorly with strong signals: I'd hear some of the "simultaneous envelope and product detection" that started me down this path.  I also noticed that with the diode ring, in the AM mode the receiver seemed to be less sensitive -- it was as if the product detector circuit was loading down the AM detector.  

One of the commenters -- Christian -- suggested putting some resistance into the input of the diode ring circuit.  I put a 150 ohm pot across the input, after the blocking capacitor. The top of the pot goes to the capacitor, the bottom to ground and the wiper to the input of L1 in the diode ring circuit (you can see the circuit in the diagram above).  With this pot I could set the input level such that even the strongest input signals did not cause the envelope detection that I'd heard earlier.  Watching these input signals on the 'scope, I think these problems arose when the IF signals rose above .7 volts and started turning on the diodes.  Only the BFO signal should have been doing that.  The pot eliminated this problem.   The pot also seemed to solve the problem of the loading down of the AM detector.  

With the pot, signals sounded much better, but I thought there was still room for improvement.  I thought I could hear a bit of RF in the audio output.  Perhaps some of the 455 kHz signal was making it into the AF amplifiers.   I looked at the circuit that Wes Hayward had used after the SBL-1 that he used as product detector in his Progressive Receiver.  It was very simple:  a .01 uF cap and 50 ohm resistor to ground followed by an RF choke.  I can't be sure, but this seemed to help, and the SSB now sounds great. 

A BETTER NAME? 

One suggestion:  We should stop calling the diode ring a diode ring.  I think "crossed diode mixer" or something like that is more descriptive.  This circuit works not because the diodes are in a ring, but because two of them are "crossed."   From now on I intend to BUILD this circuit with this crossed parts placement -- this makes it easier to see how the circuit works, how it manages to multiply by -1, and to avoid putting any of the diodes in backwards.

I prefer the bottom diagram

A KNOWN PROBLEM? 

I'm left wondering if the engineers who designed the HA-600A were aware of the shortcomings of the product detector.  It is really strange that my receivers lacks a 12V line from the function switch to the product detector. And it is weirder still that the detector works (poorly) even with no power to the transistor.  What happened there?  

When you look at the HA-600A manual, you can see a hint that maybe they knew there was a problem.  For CW and SSB, the manual recommends leaving the AF control at the quarter or halfway point, then controlling loudness with the RF gain control.  This would have the effect of throttling back the RF gain (and the potential for product detector overload) when strong signals appear.  MGC in addition to the AGC.  Any memories or insights on this would be appreciated. 

Mike WU2D Looks at the "Dream" SW Receivers of the 1960s and 70s (Video)

Wow, I really liked Mike's walk down memory lane. I saw several of my own dream receivers: 

S-38E.  Indeed, this little monster did add some danger to your life.  AKA "The Widow Maker," I gave one to my cousin's husband so he could listen to what the commies on Radio Moscow were saying.  He later told me that the receiver had given him a shock.  I now have TWO S-38Es in my shack (two more than I really need).  I have installed isolation transformers in both of them, so they have lost the one element (danger!) that made them attractive.  

HA-600A. I got this one for Christmas in 1972.  The A model is MUCH better than the plain vanilla HA-600.  I recently got another HA-600A and found serious deficiencies in the Product Detector.  Has anyone else noticed these problems?  BACKGROUND INFO AND A PLEA FOR MORE INFO HERE: https://soldersmoke.blogspot.com/search?q=HA-600A+Product+Detector

HQ-100.  Got one in the Dominican Republic.  Fixed it up, repairing damages caused by radio life in the tropics.  Disabled the goofy audio amplifier circuitry.  I now wonder if this receiver might benefit from the insertion of a 455 kc ceramic filter. 

NC190.  Wow "Cosmic Blue"  Perhaps this was an early influence that led to "Juliano Blue?" 

HQ-180.  "18 tubes and almost as many knobs!"  FB!  

HRO-500.  Love the dial. 

Transoceanic.  Never had one, but built a BFO for the Transoceanic that W8NSA took with him to SE Asia during the war. 

R-390A.  I don't have a crane for the workbench.  

Thanks Mike -- that was a lot of fun.  

Too Simple? Deficiency of the Lafayette HA-600A Product Detector?

 

I've been having a lot of fun with the Lafayette HA-600A receiver that I picked up earlier this month.  Adding to the mirth, I noticed that on SSB, the signals sound a bit scratchy, a bit distorted, not-quite-right. (I'm not being facetious;  this is an interesting problem and it might give me a chance to actually improve a piece of gear that I  -- as a teenager -- had been afraid to work on.) 

Before digging into the circuitry, I engaged in some front panel troubleshooting:  I switched to AM and tuned in a strong local AM broadcast signal.  It sounded great -- it had no sign of the distortion I was hearing on SSB.   This was an important hint -- the only difference between the circuitry used on AM and the circuitry used on SSB is the detector and the BFO.  In the AM mode a simple diode detector is used.  In SSB a product detector and BFO is used.  The BFO sounded fine and looked good on the scope. This caused me to focus on the product detector as the culprit. 

Check out the schematic above.  Tr-5 is the product detector.  It is really, really simple.  (See Einstein quote below.)  It is a single-transistor mixer with BFO energy going into the base and IF energy going into the emitter.  Output is taken from the collector and sent to the audio amplifiers. (A complete schematic for the receiver can be seen here: https://nvhrbiblio.nl/schema/Lafayette_HA600A.pdf )

I had never before seen a product detector like this.  One such detector is described in Experimental Methods for RF Design (page 5.3) but the authors devoted just one paragraph to the circuity, noting that, "We have not performed careful measurement on this mixer."  The lack of enthusiasm is palpable, and probably justified.  

A Google search shows there is not a lot of literature on single BJT product detectors.  There is a good 1968 article in Ham Radio Magazine:   http://marc.retronik.fr/AmateurRadio/SSB/Single-Sideband_Detectors_%5BHAM-Radio_1968_8p%5D.pdf      It describes a somewhat different circuit used in the Gonset Sidewinder.  The author notes that this circuit has "not been popular." 

To test my suspicion that the product detector is the problem,  I set up a little experiment.  I loosely coupled the output of a signal generator to the IF circuitry of the HA-600A.  I put the sign gen exactly on the frequency of the BFO.  Then, I switched the receiver to AM, turning off the BFO and putting the AM diode detector to work.  I was able to tune in the SSB signals without the kind of distortion I had heard when using the product detector.   

So what do you folks think?    Is the product detector the culprit?  Or could the problem be in the AGC?  Should I start plotting a change in the detector circuitry?  Might a diode ring work better?  

Some Thoughts on Singly Balanced Mixers with Two Diodes and One Transformer

In 2001, out it in the Azores, I built a 17 meter version of Doug DeMaw's Double Sideband transmitter ("Go QRP with Double Sideband" CQ Magazine, February 1997).  I struggled to understand the balanced modulator -- how it mixed, balanced, and how it produced DSB.  I later presented my understanding of the circuit in my book "SolderSmoke -- Global Adventures in Wireless Electronics" pages 132-137.   In essence, I figured out that you had to think of the balancing and the mixing as two separate operations: The transformer provided the balance that eliminated the carrier (the LO signal) while the diodes presented the two signals (audio from the mic amp and LO from the VFO) with a highly non-linear path.  The LO was successively turning on both diodes then turning off both diodes. The audio signal was being "chopped" at the rate of the LO.  This produced a complex waveform that contained sum and difference frequencies -- the upper and lower sidebands.  The carrier was balanced out by the transformer because the two outputs of the transformer were always of opposite polarity, and they were joined together at the output of the mixer.    

Fast forward to 2013.  I built a 17 meter version of Farhan's famous BITX 20 rig.  Above you can see the balanced modulator stage, which also serves as the product detector. As you can see, it is essentially the same circuit as the one used by Doug DeMaw in his DSB rig. 

In 2018 I built a simple direct conversion receiver for my nephew.  For the mixer I used what I considered to be just a cut-down  version of the circuit used by DeMaw and Farhan.  I got the idea for this from Olivier F5LVG and his RX-20 receiver from SPRAT.    It had the RF signal coming in on L1 and the VFO signal coming in to the wiper of the 1 k pot.  But with this arrangement, the diodes were NOT both being turned off on half the VFO cycle, then both being turned on during the other half.  Instead, as the VFO signal swung positive, D2 would conduct and D1 would shut down.  When the VFO signal swung negative,  D1 would conduct and D2 would shut down.  It worked, but the diodes were being switched in a very different way than they had been in the DeMaw and Farhan circuits.  If you have the strong LO signal going in on L1, BOTH diodes conduct, then BOTH don't conduct.  But if you have the LO going in through the pot, one diode conducts while the other does not conduct. 

After I concluded that the BJT product detector circuit in the HA-600A was causing distorted SSB and CW reception, I tried the old DeMaw/Farhan circuit, this time in product detector mode.  See above. This worked better, but I realized that this configuration was balancing out the BFO signal, and not the IF signal.  My problem with the original product detector had been that IF signal was getting simultaneous envelope detection AND product detection.  So I decided to just switch the inputs and put the IF signal into L1 (where it would be balanced) and the BFO into  R1/R2 (the 100 ohm pot). 

This seemed like it would reduce the envelope detection problem, right?  I mean, L1 is the balanced input, right?  But I wonder if we need to consider how the diodes were being switched in this arrangement.  Instead of having both conducting and then both not conducting, in this arrangement one would be conducting during half the BFO's cycle, while the other was not.  That means that at any given moment, the two output sides of the transformer would be looking into very different loads -- hardly a condition conducive to balance. But I used LTSpice to look at the audio output under the two different port arrangements.  Sherwood advised looking at the output of the product detector with the BFO turned off --there should be no output with the BFO off.  And indeed, putting the IF signal into L1 and the BFO into the R1/R2 pot resulted in less of the distortion causing envelope detection.  The way the diodes were being switched didn't seem to adversely affect the balancing out of the IF signal.  I am not sure why this doesn't seem to cause trouble. 

There was, however, another problem with the use of this circuit in the Lafayette HA-600A:  port isolation.  The BFO signal was getting back into the IF signal input on L1.   I could see it on the S-meter.  This was worrisome not only because of the S-meter, but also because the same circuit was driving the receiver's AGC -- in effect, the BFO was turning the gain down.  Theoretically, this should not have been happening.  Look at the transformer.  the BFO currents going through L2 and L3 should be of opposite polarities and should be cancelling each other out in L1.  But obviously this was not happening.  Perhaps this was the result of the sequential way the diode are switching in this arrangement.   On the bench, if I put the BFO into L1, I saw very little BFO signal at the R1/R2 junction. If I put the BFO signal into the R1/R2 junction, I was a lot of BFO signal at the top of L1.  And that is what I saw on my S-meter when this circuit was used in the HA-600A. 

On the bench,  if I turned off the BFO and put an AM modulated signal into the junction of R1/R2, I can see audio getting through once the input signal reaches 1 volt peak.  I do NOT see that kind of "breakthrough" envelope detection when (with the BFO off) I put a modulated signal into L1.  So the singly balanced circuit is doing that it is supposed to do -- it is balancing out the the signal going into L1. 

So it seemed that with the singly balanced circuit I would have to choose: suffer from the poor port isolation or AM breakthrough.   Clearly it was time to go for a doubly balanced circuit.  And that is what I did. 

Finally, I took a look at another two diode detector, the Polyakov or "subharmonic" detector. This is a really interesting circuit that can teach us a lot about how mixers work.  Here you can run the local oscillator at 1/2 the signal frequency.  With two diodes back to back, the incoming signal is being sampled TWICE during each cycle of the local oscillator.  That is equivalent to having the signal sampled at twice the local oscillator frequency.   This circuit allows you to run the oscillator at a much lower frequency -- this could allow much greater oscillator stability.  In the circuit above, with both diodes connected, a 7 MHz incoming signal would produce a 2 kHz tone. 

Another big plus of this circuit comes if you take D1 out of the circuit (as shown).  In this configuration the circuit becomes a normal diode detector.  Here it will receive a signal at 3.5 MHz, converting that signal into a 1 kHz audio tone.  So you can get a direct conversion receiver for 40 and 80 meters fairly easily. 

A Diode Ring Product Detector for the HA-600A? Problems.

Pete advised me to try this a week or so ago, but it took me a while to follow through and try it out.  

I got the two diode, one transformer product detector working well, but with it a new problem arose: 455 kHz energy from the BFO was leaking past the product detector back into the S-meter/AGC circuitry.  This showed up in the form of a constant S-3 reading when I switched to SSB/CW.  This was annoying. 

I figured the problem was that the only signal really being balanced out was the IF signal going into L1 of the product detector.  I took another shot at putting the BFO signal into this port, with the IF signal going into the unbalanced potentiometer port.   This did indeed take care of the BFO leakage S-meter problem, but once again the SSB did not sound great -- I think the old problem of simultaneous envelope and product detection returned.  

This was obviously a port isolation problem.  I remembered that the diode ring "doubly balanced" configuration has much better port isolation.  So on Sunday morning I built one, first in LTSpice and then on the bench.  

For the bench model I used some PC board pads out of Pete Juliano's $250,000 CNC machine.  For the toroids I used two trifilar coils wound by Farhan's dedicated staff in Hyderabad.  The diodes were sent to me by Jim W8NSA.  So there was lots of soul in this new machine. 

The circuit worked in LT Spice and at worked well when tested on my bench with my FeelTech (for the BFO) and HP8640B (for the IF signal) sig gens with my Rigol 'scope watching for the audio out.  

But I ran into some problems when I popped the new board in there in place of the old product detector:  The 455 kc BFO leakage problem is gone and the S-meter is where it should be, but...

-- I'm seeing a return of the old simultaneous envelope and product detection problem.  SSB was sounding scratchy again and indeed, when I removed the BFO signal from the diode ring circuit I could hear SSB signals making it into the audio amplifiers.  These signals sounded just like AM signals as heard through an envelope detector without a BFO. 

-- The diode ring circuit also had a very bad effect on how the HA-600A worked in AM mode.  It seemed like the new circuit was loading down the diode AM demodulator.   SW broadcast signals sounded awful in the AM mode until I disconnected the IF input to the diode ring circuit (this input is NOT switched -- it is always connected, even in the AM mode). 

So, for now, am back to using the two-diode, single transformer, singly balanced product detector with IF signal going to the balanced (L1) port and the BFO going in through the wiper of the 100 ohm pot.  

Any suggestions on how to overcome the problems with the diode ring circuit?  

The Beginning of MY Radio Life...

 

Unlike Pete (see below), I don't have any cool pictures of me in front of an early station.   But in the picture above,  there I am, at the Thanksgiving table in 1973 age 15.  I was on the air by this date, on CW as WN2QHL.  Armed with a Lafayette HA-600A and a DX-40, I was tearing up the ham bands, especially 40 meters.  Look at the tension in my face, the grip of my fist... I just wanted to finish that turkey and get on the air!  But no, I had to have Thanksgiving dinner. 

I recently realised that I have been a ham for more than 50 years. Is there an HCWA?    

This and the recent movie from India led me to think about the timeline of my early radio days: 

-- Christmas 1972.  Santa brings me a Lafayette HA-600A general coverage receiver.  With jeweled movements.  Age:  14

-- April 27, 1973.  Novice Ticket becomes effective.  WN2QHL.  Age 14. 

-- July 19, 1973.  First contact (with Elmer WN2NEC).  Age 14.

-- February 1 and 2 1973.  A grumpy old-timer calls -- during the Novice Roundup! -- to tell me that I'm putting harmonics onto the 20 meter band.  I get scared and go off the air.  Geez!  I probably just needed to retune the tank circuit.  Age 15. 

-- February 23, 1974.  I go back on the air with a DX-100.  Age 15. 

-- March 5, 1974.  I take the General Class exam at the FCC office in New York City. I pass. Age 15. 

-- April 11, 1974.  I buy the Drake 2-B from WN2NEC. This revolutionizes my radio life.  Fifteen meter contacts become possible.   Age 15. 

-- April 13, 1974.  I work ZL2ACP on 15 meter CW.  I wake up my parents to tell them.  Age 15. 

-- April 21, 1974.  END OF NOVICE OPERATION.  Apparently we were still working under a one year limitation on Novice operation.  Could the expiration date have been marked on the license? 

At this point the FCC screwed up and sent me a Technician License instead of a General Class License.  My father got on the phone to Gettysburg and straightened this out.  Thanks Dad.  So I was only a Technician for a few weeks. 

-- April 9, 1974.  General Class License effective.  I become WB2QHL,  a man of substance.  Age 15. 

-- May-June 1974.  I acquire a Heathkit HW-32A 20 meter SSB transceiver from the Crystal Radio Club.  But I have to build the power supply from an old TV.  Somehow, I survive. Age 15. 

-- June 11, 1974.  First contact with the HW-32A.  Age 15.   

-- November 9, 1974.  Last contact with the HW-32A . Age 16. 

-- March 15, 1975.  First contact with my Hallicrafters HT-37. Age 16. 

Above is my only photo of my teenage ham radio station.  I can date it via the QSL card above the map. I still have that card.  I worked W7RUK on March 25, 1975.  That contact was on 20 SSB, but when this picture was taken I was on CW (the key is plugged in, not the microphone).   

-- June 1976   I graduate from High School.  Age 17.  

-- I was active and on the air through the summer of 1976. 

-- July 1976 -- QST article on the Herring Aid 5 receiver.  I try to build it and fail.  Age 17. 

-- October 1976 -- I depart for Army Basic Training. 

There is someone else who needs honorable mention here:  My sister Trish.  Here she is, next to me at the Thanksgiving table in 1973.  Trish helped me keep my ham radio log book.  Thanks Trish! 

Pete Juliano, Field Day, 1959.  With a DX-100B and (gasp!) a QF-1. 

SolderSmoke Podcast #227: Solar System, SDR, Simple SSB, HA-600A, BITX17, Nesting Moxons? Mailbag

SolderSmoke Podcast #227 is available: 

http://soldersmoke.com/soldersmoke227.mp3

Travelogue

Mars is moving away.  Jupiter and Saturn close in the sky.  And the Sun is back in action – Cycle 25 is underway.  Also, the earliest sunset is behind us.  Brighter days are ahead.

Book Review:  “Conquering the Electron”   With a quote from Nikola Tesla. 

No real travel for us:   Hunkered down.  Lots of COVID cases around us.  Friends, relatives, neighbors.  Be careful.  You don’t want to be make it through 10 months of pandemic only to get sick at the very end.  SITS: Stay In The Shack. 

Pete's Bench and Tech Adventures:  

 Backpack SDR  keithsdr@groups.io

 Hermes Lite 2

 Coaching SSB builders

 G-QRP talk  

 A new source for 9 MHz crystal filters

 Bill's Bench: 

Fixing the HA-600A Product Detector.  Sherwood article advice. Diode Ring wins the day.  Fixing a scratchy variable capacitor.  Studying simple two diode singly balanced detectors.  Polyakov.  Getting San Jian frequency counter for it.

 

Fixing up the 17 meter BITX.  Expanding the VXO coverage.  Using it with NA5B's KiwiSDR. 

Resurrecting the 17 meter Moxon.  But WHY can't I nest the 17 meter Moxon inside a 20 meter Moxon?  They do it with Hex beams.  Why so hard with Moxons? DK7ZB has a design, but I've often heard that this combo is problematic.  Any thoughts?   I could just buy a 20/17 Hex-beam but this seems kind of heretical for a HB station.

Suddenly getting RFI on 40 meters.  Every 50-60 Hz. Please tell me what you think this is (I played a recording).  

MAILBAG:  

Dean KK4DAS’s Furlough 40/20

Adam N0ZIB HB DC TCVR

Tony G4WIF  G-QRP Vids.  Video of George Dobbs. 

Grayson KJ7UM Collecting Radioactive OA2s. Why?

Pete found W6BLZ Articles

Rogier KJ6ETL PA1ZZ lost his dog.  And we lost ours. 

Steve Silverman KB3SII -- a nice old variable capacitor from Chelsea Radio Company. 

Dave K8WPE thinks we already have a cult following.

Dan W4ERF paralleling amps to improve SNR. 

Jim W8NSA -- An old friend. 

Pete Eaton   WB9FLW    The Arecibo collapse 

John WB4GTW old friend... friend of: 

Taylor N4TD HB2HB  

And finally, we got lots of mail about our editorial.   No surprise: Half supportive, half opposed.  Obviously everyone is entitled to their opinion.  And we are free to express ours.  It’s a free country, and we want it to stay that way. That is why we spoke out.

Yesterday the Electoral College voted, finalizing the results.  All Americans should be proud that the U.S. was able to carry out a free and fair national election with record turn out under difficult circumstances. And all loyal Americans should accept the results. That’s just the way it works in a democracy.

We are glad we said what we said. It would have been easier and more pleasant to just bury our heads in the sand and say nothing.  But this was a critically important election and we felt obligated as Americans to speak out.  We'd do it again. And in fact we reserve the right to speak out again if a similarly important issue arises.  

Super-Regeneration is Super-Strange

Farhan VU2ESE is largely responsible for this.  He has recently been talking about VHF.  (More about this in due course.).  This started me thinking about my failed effort in London to get on 2 meter AM.   My plan was to use the transmit portion of this HW-30 (above) with a 2-to-10 downconverter and my trusty Drake 2-B for receive.  

Tony G4WIF also bears some responsibility:  When I expressed interest in Farhan's VHF work, Tony sent me two articles from SPRAT.  Both of them were about super-regenerative receivers.  

Farhan's comments caused me to pull the HW-30 out of storage.  I started poking around the transmitter.  But then I noticed something:  On receive, the AF amplifier was obviously working.  Then, when I tuned through the 2 meter band, the rest of the receiver seemed to be working too.  I fired up the HP-8640B sig gen on 2 meters and turned on the AM modulation.  Indeed, the old receiver was inhaling!  

This launched me into an effort to understand how super-regenerative receivers work.  There are a lot of really weak explanations out there. You get the distinct impression that the person explaining the circuit does not understand it himself.  This makes explaining it very difficult.  I am not the only one to notice this phenomenon:  Mike WU2D commented on this in one of his excellent super-regen videos.  This one:  

https://www.youtube.com/watch?v=QOhNPLT8R10

Mike very kindly said the operation of this circuit seems like "magic."  I was thinking more in terms of Voodoo.  

Howard Armstrong discovered super-regeneration years after he invented plain old regeneration.  The new discovery came around 1921.

It looks like VHF guru Frank Jones had very early misgivings about super-regeneration.  In his 1934 classic 5 Meter Radio Telephony, Jones seems unenthusiastic about the circuit and about our ability to understand it:  "To explain, simply, exactly how this form of detection takes place is not a simple matter, but some of its characteristics are easy to visualize."  In this book, Jones goes on to predict that super-regens will be superseded (!) by superhets.  Indeed, in his 1961 book VHF for the Radio Amateur there are no super-regen circuits; all the receive systems are down-converters to HF receivers. 

Still, with that HW-30 hissing away right next to me, I feel I need to understand how the super-regen works.  I'm not there yet, but I'm trying.  Here are some good resources: 

A good article from Wireless World 1946:  

http://www.r-type.org/articles/art-285.htm  

A student's write up of his effort to understand: 

https://folio.brighton.ac.uk/artefact/file/download.php?file=597679&view=111191

But the best so far (for me) is from Frederick Terman (one of the founders of Silicon Valley) in  his 1943 classic Radio Engineer's Handbook.  Click on the images for a clearer view. 

I will definitely try to get the HW-30's 5 watt AM transmitter going.  I am not so sure I'll do anything with the receiver.  I think this is a matter of picking your battles and "finding joy."   I didn't find joy in FT-8, so I stopped working with it.  Same with my HA-600A, DX-40 Novice rig.  Same with CW in general.  And the same with SDR.  I suspect that super-regen receivers may also fall into this category.  I mean, let's face it, if you are not fond of ordinary regens, is there any real chance that you will like SUPER-regens?  Even Frank Jones seems to have disliked them.  And there is a reason Howard Armstrong moved on to superhets -- they are better! But still, that receiver is hissing away at me...  Stay tuned. 

SolderSmoke Podcast #226 The U.S. Election, Solar Cycle, uSDX, Hermes, HP8640B, SGC 600 Sig Gen, HA-600A, Mailbag

SolderSmoke Podcast # 226  

http://soldersmoke.com/soldersmoke226.mp3

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About the U.S. election

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Mars:  Setting early, will have to shift to evening observation.  Weather has been poor. 

Sunspot Cycle 25 is underway -- SFI 78, SN 32  

The Gliessberg cycle

Pete's Bench:  #49,  #50,  uSDX,  Hermes Lite

Bill's Bench: HP8640B,  Global Specialties Corp 6000 counter, Lafayette HA600A.

MAILBAG:

Peter VK2EMU Sent me copy of 1947 Handbook.  Thanks Peter

Brad W1BCC Spotted 10 S-38s for 80 bucks on Craig’s list.  What’s going on here? 

Dale K9NN sent both Pete and I care packages with very cool part, including DG Mosfets

Stuart ZL2TW sent me Les Moxon’s Antenna Book.  TRGHS. Moxon will be back! 

Alvin N5VZH got his receive converter with a little Tribal Knowledge from SS. 

GM4OOU The Bitsy DSB rig from Scotland

Peter VK3YE DSBto DC incompatibility SOLVED

Paul VK3HN's Digital SWR and Power Meter and Low band AM TX VFO/Controller FB Videos. 

VK2BLQ alerts us to article about Jac Holzman of Elektra Records. 

AA0ZZ great message on assembler language and writing software the hard way. 

So Many Wonderful Things on W7ZOI's Site

 

There he is.  Wes Hayward, W7ZOI in 1957.  I had never seen this picture before.  I found it on Wes's recently updated "shackviews" web page: http://w7zoi.net/shackviews.html . 

There are so  many treasures on that page, and on all the other portions of Wes's site.

Some highlights for me: 

-- Wes's description of the station in the above picture. 

-- On his page about Doug DeMaw, Wes mentions that after Doug edited Wes's 1968 article about direct conversion receivers, Doug built some himself, experimenting with different product detector circuits. Having used Doug's mixer circuit in many of my rigs, and having recently experimented with different product detectors for my HA-600A, I kind of felt like Doug was watching over my shoulder, guiding me along as I experimented. 

-- Wes's use of a digital Rigol oscilloscope.  Makes me feel better about giving up on my Tek 465. 

-- The page about Farhan's visit to Wes, and the awesome gathering of homebrew Titans that ensued... 

-- Wes's meeting with Chuck Adams.  

Thanks Wes.  Happy New Year and best of luck in 2021!  

Putting the "Mate for the Mighty Midget" Back to Work -- With a DX-100 on 40 Meter AM

After working on it for a while I got so fond of my old Hammarlund HQ-100 that I moved it from the AM/Boatanchors operating position over to a more convenient spot right next to my computer.  This left a big gap on the receive side of the AM station.  

I briefly put my HRO-ish solid state receiver above the DX-100, but I'm afraid that receiver needs some work.  More on that in due course. 

I thought about putting my SOLID STATE Lafayette HA-600A atop the thermatronic DX-100, but this just didn't seem right. The Radio Gods would NOT approve. 

So I turned my attention to the Mate for the Mighty Midget that I built in 1998 and have been poking at and "improving" ever since. 

This receiver worked, but not quite right. It received SSB stations well enough, but when I turned off the BFO I could no longer hear the band noise. I wasn't sure how well the RF amp's grid and plate tuned circuits tracked.  And I had serious doubts about the detector circuit that Lew McCoy put in there when he designed this thing back in 1966. 

As I started this latest round of MMMRX poking, I realized that I now have test gear that I didn't have in 1998:  I now have a decent oscilloscope.  I have an HP-8640B signal generator (thanks Steve Silverman and Dave Bamford).  I have an AADE LC meter. And I've learned a lot about building rigs. 

FRONT END TRACKING

The MMRX has a tuned circuit in the grid of the RF amplifier, and another in the plate circuit of the RF amplifier.  There is a ganged capacitor that tunes them both.  They need to cover both 80/75 and 40 meters. And they need to "track" fairly well:  over the fairly broad range of 3.5 to 7.3 MHz they both need to be resonant at the same frequency.  

McCoy's article just called for "ten turns on a pill bottle" for the coils in these parallel LC circuits.  The link coils were 5 turns.  No data on inductance was given.  Armed now with an LC meter, I pulled these coils off the chassis and measured the inductances of the coils.  I just needed to make sure they were close in value.  They were: 

L1 was .858uH L2 was 2.709         L3 was .930uH  L4 was 2.672

Next I checked the ganged variable capacitors.  At first I found that one cap had a lot more capacitance than they other.  How could that be?  Then I remembered that I had installed trimmer caps across each of the ganged capacitors. Adjusting these trimmers (and leaving the caps connected to the grid of V1a and V2A, I adjusted the trimmers to get the caps close in value.  I think I ended up with them fairly close: 

C1: 63.77-532 pF          C2 64.81 -- 525.1 pF

I put the coils back in and checked the tracking on 40 and on 80/75.  While not perfect, it was close enough to stop messing with it.  

DETECTOR CIRCUIT

I've had my doubts about the detector circuit that Lew McCoy had in the MMMRX.  In his 1966 QST article he claimed that the circuit he used was a voltage doubler, and that this would boost signal strength.  But I built the thing in LT Spice and didn't notice any doubling.  And consider the capacitors he had at the input and output of the detector:  100 pF.  At 455 kHz 100 pF is about 3500 ohms.  At audio (1 kHz) it is 1.5 MILLION ohms. Ouch.  No wonder years ago I put a .1 uF cap across that output cap just to get the receiver working. 

Scott WA9WFA told me that by the time the MMMRX appeared in the 1969 ARRL handbook, the second "voltage doubling" diode was gone, as were the 100 pF caps.  Now it was just a diode, a .01 uF cap and a 470,000 ohm resistor.  I switched to the 1969 Handbook circuit (but I have not yet changed the 1 meg grid resister to 470k -- I don't think this will make much difference).  Foiled again by a faulty QST article, again by one of the League's luminaries. 

6U8s out, 6EA8s in 

We learned that the 6U8 tubes originally called for by Lew McCoy are getting old and not aging well.  So I switched all three to more youthful 6EA8s.  This seemed to perk the receiver up a bit. 

MUTING from the DX-100

My K2ZA DX-100 has a T/R relay mounted in a box on the back of the transmitter.  When the Plate switch goes up, it switches the antenna from receiver to transmitter.  The box also has a one pole double throw switch available for receiver muting.  I put the common connection to ground, the normally connected (receive position) connect the ground terminal of the AF output transformer to ground -- it is disconnected from ground on transmit.  The other connection (normally open) is connected to the antenna jack -- on transmit this connection ground the receiver RF input connection.  These two steps mutes the receiver very nicely. 

Replacing Reduction Drive

Over the years I have had several different reduction drives on the main tuning cap.  I had a kind of wonky Jackson brothers drive on there that needed to be replaced.  I put in a new one -- this smoothed out he tuning considerably. 

Ceramic Resonator

I never could get McCoy's 455 kc two crystal filter to work right.  So at first I made due with the two 455 kc IF cans.  This made for a very broad passband.  Then I put a CM filter in there.  This was more narrow, but with a lot of loss.  There may have been others.  But the filter spot is currently held by a 6 kHz wide ceramic filter.  This one is my favorite so far. 

Digital Readout

When I was running the DX-100 with the Hammarlund HQ-100 I built a little frequency readout box.  The box was from a Heath QF-1 Q multiplier (I am sorry about this).  The readouts are in Juliano Blue and come via e-bay from San Jian.  I now have it hooked up to the DX-100's oscillator.  I haven't tapped into the MMMRX's oscillator yet. 

A Problem with the San Jian PLJ6-LED Counter

I had hoped to use this handy and cheap little frequency counter to add some glowing Juliano Blue to the frequency readout on my Quarantine Hodgepodge rig.   I've used these boards with my BITX20, my HA-600A,  and with my DX-100/HQ-100 rigs.  But guess what -- these boards do not work with the BITX40 module board that is the heart of the Quarantine Hodgepodge.  And the reason why is interesting. 

Here is what happens:  First, you plug in the IF frequency of your rig.  In my case 12 MHz.  You connect your VFO output to the signal input on the PLJ6.  You power up the PLJ6.  You then have to select one of two IF frequency options.  One of these options ADDS your IF frequency to whatever it detects at the signal input.  In my case, for a 7.2 MHz signal it would detect a VFO signal at 4.8 MHz. If it were to ADD this signal to the IF freq,  it would readout 16.8 MHz.  And it does.  But obviously that is wrong.  So you go to the other option -- this one SUBTRACTS the designated IF frequency FROM whatever it finds at the signal input.  So here we get 4.8 - 12 =  -7.2   Almost perfect right?  But here is the problem:  The PLJ6 can't handle negative numbers!  So it displays 000000.  Not helpful. 

Here is the manual: 

https://www.mpja.com/download/35057tebasic%20manual.pdf

I didn't have this trouble with any of the other rigs because none of them required the use of negative numbers.  My BITX 20 for example had an IF of 11 MHz and has the VFO running a bit above 3 MHz -- so the PLJ6 just adds the IF to the VFO signal and Bob is my uncle.  Similar problem-free addition takes place with the other rigs. 

I found some discussion on this problem on the internet.  Here is one: 

https://groups.io/g/BITX20/topic/bitx40_and_plj_6led_frequency/4330098?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,4330098 

Some of the respondents didn't seem to understand the problem.  Others hint that the ability to handle negative numbers was as some point in the code for the PLJ6 device,  and may somehow be accessible, but no further info is provided. 

I have already worked up a possible solution, but I'm interested in how you folks would approach this problem.   Any thoughts or suggestions?  I will reveal my solution in the days ahead.