50 Shades of Homebrew? PH2LB's Shack and NanoVNA Adapters

 

That would have been a very different movie.   And I don't think the box office results would have been favorable.  That's PH2LB's "pleasure room" (shack). He has a good blog focused on homebrew: 

https://www.ph2lb.nl/blog/index.php?page=history   

Lex has also  made some very cool adapters for measuring filters with the NanoVNA: 

https://www.ph2lb.nl/blog/index.php?page=qrp-labs-filter-adapter-for-nanovna 

Thanks Lex. 

QST Recognized Error on Sideband Inversion, But Continued to Make the Same Mistake

 

I don't really know if this is good news or bad news.  It's good that in November 1985 they recognized the error, but then they allowed the same error to be repeated by the same author in the 1989 article "A Four-Stage 75-Meter SSB Superhet," and again in 1990 in W1FB's Design Notebook.   It also made it into the 2002 ARRL Handbook.  

Thanks to Chuck WB9KZY for alerting us to this Feedback piece. 

QST Repeatedly Got Sideband Inversion Wrong

It kind of pains me to do this. These articles are from a long time ago, and the author is an esteemed  Silent Key,  but the myth about the origins of the USB/LSB convention is still out there, and as a homebrewer of SSB gear I feel obligated to point out these examples of the error that that myth is based on.   

Last Friday, Pete WB9FLW and I were talking about homebrewing SSB rigs.  I recommended a series of QST articles by Doug DeMaw.  "Beginner's Bench:  The Principles and Building of SSB Gear" started in QST in September 1985. There were at least five parts -- it continued until January 1986. (Links to the series appear below.) I hadn't looked at these articles in years, but when I did, a big mistake jumped right out at me:  In the first installment, on page 19, Doug  makes the same mistake that he made in his Design Notebook:

"Now comes the conversion section of our SSB generator.  We must move (heterodyne) the 9-MHz SSB signal to 3.75-4.0 MHz. Our balanced mixer works just as it does in a receiver. That is, we inject the mixer with two frequencies (9 MHz and 5 MHz) to produce a sum or a difference output frequency (9 - 5 = 4 MHz, or 9 +5 = 14 MHz) If we are to generate 75 meter SSB energy, we must chose the difference frequency. We could build an 20-meter SSB transmitter by selecting the sum of the mixer frequencies. The RF amplifiers and filter (FL2) that follow would then have to be designed for 14-MHz operation.  In fact, many early two-band homemade SSB transmitters were built for for 75 and 20 meters in order to use this convenient frequency arrangement.  The use of upper sideband on 20 meters and lower sideband on 75 meters may be the result of this frequency arrangement (the sidebands become inverted when switching from the difference to the sum frequency.) " 

Those last two sentences are incorrect.  They repeat the "Myth," or the "Urban Legend" about the origins of the LSB/USB convention.  Contrary to what many hams now believe, with 9 MHz filter and a 5.2 MHz BFO it takes more than just switching from sum frequency to difference frequency to invert one of the sidebands. 

There are two conditions needed for sideband inversion to take place:  

1) You have to be taking the difference product (DeMaw got that right) 

2) The unmodulated (VFO or LO) signal must be larger than the modulated signal. (DeMaw and the ARRL obviously missed that part.  Repeatedly.) 

This is another way of stating the simple, accurate and useful Hallas Rule:  Sideband inversion only occurs when you are subtracting the signal with modulation FROM the signal without modulation. 

For DeMaw's claim to be correct, one of the SSB signals going into the balanced mixer would have to invert, and the other would have to not invert.  Let's see if that happens: He has the sideband signal being generated at 9 MHz and the VFO running around 5 MHz. 

9 - 5 = 4  But we are not subtracting the modulated signal FROM the unmodulated signal.  SO NO INVERSION

9 + 5 = 14   We are not subtracting at all.  SO NO INVERSION.  

Doug's convenient frequency scheme WOULD work if he'd just switch the frequencies of the filter and the VFO.  With a sideband generator on 5.2 MHz and a VFO around 9 MHz you do get the happy 75  LSB, 20 USB arrangement without the need to switch the carrier oscillator/BFO frequency.   That is what happened in the Swan 240, and that is what I have in my Mythbuster rig. I am listening to both 75 LSB and 20 USB without changing the carrier oscillator/BFO frequency.  My filter/BFO/product detector is set up for USB.   With this arrangement the 75 meter LSB signals DO invert, and the 20 meter USB meter signals do not, so both are able to make use of my USB BFO/product detector without shifting the BFO frequency. 

This error shows up again in DeMaw's the May 1989 QST article "A Four Stage 75-meter SSB Superhet" (reprinted in the ARRL's QRP Classics book).  Here he writes: 

"Should you want to cover both the 75- and 20-meter bands you can build a 20-meter version of FL-1 and band switch the two filters. As with the 75 meter only version, an IF of 9.0 MHz (Y1) is required. With this arrangement the 20 meter band will tune backwards from the 75 meter band, but upper- and lower-sideband reception will occur, as required, without changing the BFO frequency (Y2). This two band scheme with a 5-MHz VFO is an old one!"   NOTE: FL1 is the bandpass filter, not the IF filter.  

Doug's mistakes in this area may simply be due to the fact that he was more of a CW guy.  And this is something that is quite easy to confuse:  9 and 5 will get you to 75 and 20, but you have to make sure the VFO is at 9 if you want to make use of sideband inversion and avoid having to shift the BFO/ carrier oscillator.   I've made this mistake myself: 

https://soldersmoke.blogspot.com/2012/05/usblsb-urban-legend-debunked.html

In October 1993 I wrote to DeMaw about his Four Stage 75 meter SSB Superhet.  I think I was looking for details on how to put it on 20 meters.  As I recall, Doug wrote back telling me to just pick 20 meter values for the input bandpass filter.  Had I done so, I would have discovered that  -- for the reasons cited above -- this just wouldn't have worked on 20.  His BFO and filter were set up to receive LSB signals. That's fine for the incoming 75 meter LSB signals.  But on 20 -- contrary to DeMaw's thinking -- there would be NO sideband inversion. I'd be trying to listen to 20 meter USB signals with a receiver set up for 20 meter LSB.  

Did anyone else notice these errors.  Were there ever errata notices in QST on this?  

This is a reminder that you should take all technical articles and schematics with a grain of salt.  Many contain errors. We are all human, and this is a complicated subject with lots of details. 

https://pe2bz.philpem.me.uk/Comm/-%20ARRL/Build-Service-Design/Receivers/PrincipleOfBuildingSSBgear/8509017.pdf

https://pe2bz.philpem.me.uk/Comm/-%20ARRL/Build-Service-Design/Receivers/PrincipleOfBuildingSSBgear/8510027.pdf

https://pe2bz.philpem.me.uk/Comm/-%20ARRL/Build-Service-Design/Receivers/PrincipleOfBuildingSSBgear/8511016.pdf

https://pe2bz.philpem.me.uk/Comm/-%20ARRL/Build-Service-Design/Receivers/PrincipleOfBuildingSSBgear/8512037.pdf

https://pe2bz.philpem.me.uk/Comm/-%20ARRL/Build-Service-Design/Receivers/PrincipleOfBuildingSSBgear/8601029.pdf

Possible Victory for Frank Jones and the FMLA? Could We Get the 5 Meter Band Back?

 

EI7GL reports some very interesting IARU activity that could possibly result in the 5 Meter band coming back to amateur radio use:  

"The 60 MHz or 5 metre band has the potential to be a future allocation for the Amateur Radio service. The International Amateur Radio Union (IARU) are currently encouraging member societies to try and obtain small allocations at 40 MHz and 60 MHz."

https://ei7gl.blogspot.com/p/60-mhz.html

Regaining 5 meters was, of course, the objective of Frank Jones and the Five Meter Liberation Army.  Wouldn't it be great of Michael Hopkins' fictional tale actually ended up coming true!  

Mr. Carlson's New Lab. And his Amazing Tek Collection

The Unicorn! A 75 LSB /20 USB Receiver (That Can't Work)

 

Don't get me wrong -- I'm a huge fan of Doug DeMaw.  His books and articles are a treasure trove for ham radio homebrewers.  Also, Doug was an honest guy who admitted in the preface to his QRP book that at times he did not fully understand the circuits he was building; that kind of honesty is rare,  and is very helpful to amateurs who struggle to understand the circuits we work on.  

But everyone makes mistakes, and Doug made one in his "W1FB Design Notebook."  I present it here not as a "gotcha" effort to nitpick or sharpshoot a giant of homebrew radio, but because this error illustrates well the depth of the 75 LSB/20 USB myth, where it comes from, and how important it is to really understand sideband inversion.     Here is the mistake: 

That's just wrong.  A receiver built like this will not allow you to listen to 75 LSB and 20 USB "without changing the BFO frequency." (Am I the first one to spot this error?  Didn't anyone build this thing, only to discover that it, uh, doesn't work?)

Here's a little drawing that I think illustrates why the mythical scheme will not work: 

All confusion about sideband inversion could be avoided with the simple application of what I think we should call "The Hallas Rule": 

"Sideband reversal occurs in mixing only  if the signal with the modulation is subtracted from the signal that isn't modulated."  

Be careful here:   I think some arithmetic carelessness is responsible for much of the myth. Taking the difference frequency is not enough to produce sideband inversion. Read the Hallas Rule carefully:   For sideband inversion to occur, the signal with the modulation must be subtracted FROM the signal without the modulation.

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

About the Swan 240's SSB generation scheme: 

I first stumbled on this problem when building my first SSB transmitters in the Azores.  I was using a VXO,  and a filter pulled out of a Swan 240 (5.173 MHz).  I started with VXO crystals at around 12.94 MHz.  The rig worked,  but I couldn't pull the VXO crystals very far.  So I switched to crystals at around 23.3 MHz (you can pull higher frequency crystals farther).  But look what happened:  My Carrier Oscillator frequency had been set up to receive USB signals on 17 Meters.  With the 12.94 MHz rocks, that worked fine:   18.150-12.977 = NO INVERSION.  But it all changed when I went to the 23 MHz VXO rocks:  23.323-18.150 = INVERSION!   This had me scratching my head a while.  I had to draw myself little spectrum pictures (like the one above) before I realized what had happened.  To get it to work -- to get it to produce USB on 17 meters -- I had to move the Carrier Oscillator to the other side of the passband. Good thing that Swan 240 came with TWO BFO crystals (5.1768 MHz and 5.1735 MHz). I just had to change the crystal. 

For 75 and 20 meters, the Swan 240 uses the correct 5.173 MHz filter with a 9 MHz VFO to get the happy situation of 75 meter LSB and 20 Meter USB WITHOUT changing the BFO/Carrier Oscillator frequency.  This is the Mythbuster scheme.  Unlike Doug's receiver, it works.  The scheme also works in the Swan 240 on 40 meters because for 40 the Swan rig has the VFO running from 12.073 MHz to 12.513 MHz. Here too, no change in the BFO/Carrier Oscillator  frequency is needed. But the Swan recommended a modification that would allow operation on 20 LSB and 75/40 USB!  It used a BFO/Carrier Oscillator crystal of  5.1765 MHz and a switch mounted on the front panel.  Luckily,  my junker Swan (acquired from HI8P in the Dominican Republic) had the second crystal -- mine was 5.1768 MHz.  It was that crystal that allowed me to get my Azorean SSB transmitter to work using the 23.9 MHz VXO rocks.    

Ganymede and Jupiter as seen by Juno

But remember the warning:

"All these worlds are yours, except Europa.  Attempt no landing there." 

Mythbuster Videos 8 and 9 -- The Old Military Radio Net plus "Zero Beat and The Vertical Skirts"

I like to listen to the Old Military Radio Net on Saturday mornings. This week I was listening with the Mythbuster receiver. The AM carriers provided a good opportunity to observe the effects of the steep skirts of the 10 pole crystal filter. We start at zero beat, with the BFO exactly on the carrier frequency. If I turn the VFO dial in one direction, I in effect move the passband in a way that puts the carrier in the passband. And it is no longer zero beat with the BFO, so we hear the heterodyne (the beat!). But if I turn the VFO dial in the other direction, the carrier is now outside the passband. Even though the BFO would produce a tone, we don't hear a tone, because those steep filter skirts are keeping the carrier out. We do continue to hear some of the sideband frequencies, because they remain in the passband. The very sharp drop-off of the carrier tone is a good indication that the steep skirts of the crystal filter are doing the job.

"Zero Beat and the Vertical Skirts" Sounds like the name of a Punk Rock band, doesn't it? Anyway in this video I explain what happened in Mythbuster Video #8 (above). I explain why we can hear the Old Military Radio Net carriers when I tune the VFO in one direction, but not in the other.

Michael Newton Hopkins, AB5L, Author of the FMLA series

Better than anyone else ever has, Michael Hopkins, in his fictional series about Frank Jones and the Five Meter Liberation Army, captures the spirit of homebrew radio.  There is just so much of us in those articles.  I read them some 20 years ago when they first came out; reading them again recently I appreciated them even more.  

Frank was a bit of a curmudgeon:  There are jabs at the appliance operators, Hiram Percy Maxim, hamfests, SSB, the Collins collectors, the QRP movement,  and even Electric Radio magazine.  Howard Armstrong makes an appearance, as do Carl and Jerry.  It all made me want to put a five pin SAW filter on my lapel.  

As I read, I thought about what a great writer Michael was.  When I Googled him, a few of the results led me back to  my own book.  I'd forgotten that Michael was in there, but he is.  On one page he advises me how to power my Mate for the Mighty Midget receiver without using a power transformer (a very Frank Jones approach).  On another page I note that Michael had sent me a kit for the Doug DeMaw "Barbados Receiver."  Wow, that was my first Superhet.  (I also have one that was built by Dale Parfitt.)  Most of the parts were put to use in other projects.  But I still have the board (see above).  Reminded that it came from Michael, I will now have to complete the construction.

Below is a nice article about Michael that appeared in the Flying Pigs newsletter. (Click on the images for an easier read.)   

The articles can be found here: 

http://soldersmoke.blogspot.com/2021/07/summer-reading-for-homebrewers-frank.html

Michael's 2005 Obituary:

https://obits.dallasnews.com/us/obituaries/dallasmorningnews/name/michael-hopkins-obituary?pid=14406223

Thank you Michael.  VIVA EL FMLA! 

Alan Wolke W2AEW's Great Video on Using NanoVNA to Measure Amplifier Input Impedance and Gain

Alan Wolke W2AEW is a true wizard.  We are all lucky to be interested in homebrew radio at the same time that he is sharing his knowledge and wisdom via YouTube. 

The ability of the NanoVNA to measure circuit impedances is, in my mind, one of its most valuable features.  With this, we can MEASURE input and output impedances.  We can put bits and pieces of circuitry together without wondering whether or not we were introducing impedance mismatches.   

But I had trouble getting good NanoVNA impedance readings on my TIA amps. I wrote to Alan about this and he pledged to make a video about how to do it right.  That video was posted to YouTube today (see above).  

Not only did I learn how to get a good impedance reading, I really learned a lot by just watching Alan move around through the various NanoVNA screens.  I want to be able to do that too!  I want to monitor the Smith Chart, and gain, and SWR, all at the same time.  Yes I do!  I also now realize that I have to order a bunch of those cool PC board SMA female connectors from Bezos. 

Thanks a lot Alan.  

Frank Jones's 1936 Radio Handbook

 

https://worldradiohistory.com/BOOKSHELF-ARH/Handbooks/Radio-Handbook-4-1936.pdf

Mythbuster Video #7: Bandswitch, Reverse Polarity Protection, CW with Clarifier Offset

I have the speaker mounted on the front of the board. I kind of like it like that. I now have a bandswitch, and reverse polarity protection (no more living dangerously for me). That Yaesu VFO clarifier circuit might prove useful should I decide to give this rig CW capability. I once again find myself thinking that I might never put this in a metal box. Frank Jones had the right idea.