How to Fix the Spur Problem in my 17 Meter SSB Transmitter?

 

I built the transmitter almost 20 years ago.  It is in the larger box, which originally housed a Heathkit DX-40.  There is a lot of soul in that old machine.  Details on this construction project are here: https://soldersmoke.blogspot.com/2021/12/junk-box-sideband-from-azores-2004-qst.html  (The smaller box is a Barebones Superhet receiver set up for 17 meters.) 

In the 2004 QST article I discuss a problem I had with "spotting" or "netting."  This is something of a lost art, something that you had to do back in the pre-transceiver days, when running a separate transmitter and receiver.  This was how you got the transmitter on the receiver's frequency.  Essentially you would turn on the carrier oscillator and the VFO and let a little signal get out, enough to allow you to tune the VFO until you heard zero beat on the receiver.  My problem was that around one particular frequency, I would hear several zero-beats.  This made netting the receiver and the transmitter hard to do.  

Important note:  This is really just a problem with the "netting" or "spotting" procedure -- the problematic spur does not show up in any significant way in the output of the transmitter.  I can't see it on my TinySA.  But it is strong enough to be heard in the unmuted receiver sitting right next to the transmitter. And that creates the netting problem. 

In the QST article, I said that I noticed that the problem seemed to be centered around 18.116 MHz.  As I approached this frequency, the tones -- desired and unwanted -- seemed to converge. That was an important clue.  In the article I said I thought that I could eliminate the problem with just one trimmer cap to ground in the carrier oscillator, but looking back I don't think that this really fixed the problem. 

I recently took a fresh look at it.  Exactly which frequencies were causing the unwanted signals that appeared in my receiver? 

I used an Excel Spread sheet to find the culprits. 

The first column shows the carrier oscillator and its harmonics.  The second column shows the VFO when tuned for a signal at 18.11668 MHz (23.2927-5.17602), along with its harmonics.  Check out the 10th harmonic of the carrier oscillator and the third harmonic of the VFO: 69.8781-51.7602 = 18.1179.   Those two harmonics would produce the problem I had been experiencing. 

I turned to one of Wes Hayward's programs for confirmation.  Spurtune08 came in the EMRFD software package. Here is what I saw when I plugged in the above frequencies:    

You can see the little spur off to the left of the main signal.  In the program, as I tune the 23 MHz VFO frequency, the spur moves closer to the main frequency as I approach 18.116 MHz, just as it does in the real rig.   Note that I have only turned on the 10th harmonic of the carrier oscillator and the 3rd harmonic of the VFO.  Spurtune08 is very useful.  Thanks Wes! 

So, what is to be done?   For now, I am just restricting my operations on 17 meters to above 18.120 MHz.  (I worked several DX stations with it on December 27.)  But obviously I need to fix this. This rig needs an exorcism.  I think I only need to get rid of one of the harmonics, and the 10th harmonic of  the carrier oscillator seems easier to kill.  I'm thinking of putting the carrier oscillator in an Altoids box, and then adding some filters to knock down the 10th harmonic. 

Here is the G3YCC schematic that inspired this rig.  I used G3YCC's carrier oscillator and balanced modulator circuits, just using a 5.176 MHz crystal and changing the tank circuit in the collector: 

How would you folks knock down that 10th harmonic? 

A Christmas Story: Mike AA1TJ Builds Receiver for 486 kHz, Listens to Fessenden Commemoration (Audio)

Mike's 486 kHz receiver

As if being able to get home on Christmas Eve 2021 and then catching the Webb Telescope launch was not enough, Santa had another gift for us:  Michael Rainey, AA1TJ, the Homebrew Hero of the Hobbit Hole, was back at it, melting solder. Mike threw together a regen receiver that allowed him to receive a transmission commemorating Reginald Fessenden's historic first transmission of phone signals.  I was really pleased to once again be able to read about an AA1TJ radio adventure.  Thanks Mike!  Here is what Mike heard: http://soldersmoke.com/AA1TJ 920km.mp3

Mike wrote: 

My chum, Peter/DL3PB, recently told me that Brian/WA1ZMS would broadcast a commemoration of Reginald Fessenden's mythical (operative word) 1906 Christmas Eve AM transmission. Doesn't that sound like fun?

True to form, I began scratch-assembling my receiver yesterday afternoon just as Brian went on the air. Then again, a two-transistor regenerative radio for 486kHz isn't exactly rocket science. In any case, I was up and listening inside of a half hour.

 
What did I hear? Static. Just static. As a sanity test I quickly tuned down to 371KHz to find my favorite non-directional beacon, "GW," beaming in loud and clear from Kuujjuarakip.

 
Kuujjuarakip?

Kuujjuarakip is a tiny settlement of mostly Inuit and Cree inhabitants located up on Hudson Bay. The villages are primarily accessible by air and water so a robust radio beacon is an obvious necessity.

 
Satisfied that my receiver was working properly, I re-tuned to 486kHz. Back to static. On the bright side, at least there were no commercials. I continued listening intently until Vic called me to dinner. After the dishes were done I slipped back down to my underground radio shack for one last try.

I heard it right away. Beneath the static I heard a weak, out-of-tune, solo violin playing, "Oh, Holy Night." The signal strength varied wildly with ionospheric propagation. When the signal finally climbed high enough above the noise I ripped out the bipolar transistor audio amplifier stage, connecting my headphones directly to the junction field effect transistor detector output terminals. Of course the audio was far weaker now, yet I could easily follow the tune until it eventually faded away. Not bad for an estimated 15 watt ERP AM signal from a distance of 920km. And on 486kHz, no less, just a hop-skip-and a jump from the old 500kHz Maritime CW band; where countless ship radio operators went to send their last SOS.

 
Returning to the house, I emailed my reception report and included a short recording that I had made of it. Brian replied just after midnight; apparently, equally as stoked

"Yours’ is the best DX ever given your regen RX! Way to go! I just love it."

He went on to tell me that he was born and raised in Vermont, but he'd been working as a radio scientist down in Virginia since 1990. Told me his heart was still here in the Green Mountains and he was touched to learn his meager signal had found its way back there on Christmas Eve. All in all, a night to remember.

 
If you're still with me I hope you'll listen to the short NPR story in the provided link. It originally aired on the supposed 100th anniversary of this event. It's not just about radio history. It's about belief, memory and the myths we lug around in our heads. I thought it was well done.

 
Cheers,
Mike

Listen to what Mike heard. He says he "merely connected the mic input line of my computer across the headphone terminals. Some of the noise in the recording, - certainly the higher frequency stuff - is a byproduct of the computer. The headphone audio with the computer switched off was much more pleasant."  Here it is: http://soldersmoke.com/AA1TJ 920km.mp3

NPR story (audio and text)

https://www.npr.org/2006/12/22/6665738/christmas-eve-and-the-birth-of-talk-radio?fbclid=IwAR1G3ZchgTCc2EDnkS5BCxGARwsa87bvf0LO9nd5hfLQDvb96fR6w0dBzw4

A Nice Christmas Gift Out of French Guiana -- The Launch of the James Webb Space Telescope

 

A nice Christmas present from NASA and ESA on the screen early on Christmas morning.  

Track Webb Telescope's progress here: 

https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

The (Real) Solar Flare of August 1972 in Cixin Liu's Science Fiction

 

A view of McMath Region 11976 from the Paris Observatory early on 4 August 1972. 

I have a vivid memory of seeing -- as a kid -- Aurora from our home near New York City.  Eric Carlsen, my childhood friend and colleague from the Waters Edge Rocket Research Society,  told me his mom had similar memories. A while back I did some Googling and concluded that it had to have been the monster solar flare of  August 1972:

 https://soldersmoke.blogspot.com/2009/09/carrington-flares-aurora-where-were-you.html    

That blog post got about eight comments, mostly from other folks with similar memories -- they apparently were led to my blog by the same kind of memory-based Googling that I had done. 

This year, on Christmas Eve, Elisa and I were flying home from the Dominican Republic. I was reading (on my phone) "To Hold Up the Sky," an anthology of Cixin Liu's science fiction short-stories.   I'd read his excellent "Three body Problem" in the Dominican Republic back in December 2017.   His work is usually "hard" sic-fi, with a strong connection to real physics.

One of the short stories in the anthology is entitled "Full Spectrum Barrage Jamming." Wow, I thought, that one is really promises to be very interesting for a radio amateur.  I turned out that it was more interesting than I expected. 

I won't spoil the story for you.  Suffice it to say that Cixin Liu makes reference to the same August 1972 solar flare that I remember from my childhood, and discusses its effect on radio propagation.  It was really kind of eerie to be in that plane, flying over the Bahamas, reading Chi-Fi on my I-phone, and seeing the author reference that memorable event from 1972.  TRGHS. 

There were plans to turn this story into a movie: https://www.yicaiglobal.com/news/wandering-earth-producer-to-film-another-liu-cixin-novel

Here is an excellent article describing what happened back in 1972: https://room.eu.com/article/lessons-from-the-sun.   The August 1972 flare was so strong that it caused U.S. Navy anti-ship mines to explode in Haiphong harbor in Vietnam. 

On 17 meter CW from Santo Domingo with a uBITX

We are up on the 12th floor of a building in Santo Domingo. I brought my uBITX and managed to check in as baggage a 16-foot crappie fishing pole. I figured I needed to get the 1/2 wave antenna away from the building -- last time I was here I was unable to make any contacts from this location with the antenna stretched along the balcony. Last time I was QRP with an SST transceiver. 

The fishing pole worked well, but I operated with fear that it would fall or that the neighbors would complain). Today I got on 17 CW with the uBITX (more power than the SST), put it on 17 CW and promptly worked W4A, a special events station commemorating E. Howard Armstrong.  Turns out that today is Armstrong's birthday.  TRGHS.  

On the Reverse Beacon Network my CQs were heard by KO7SS in Arizona (very cool skimmer station at 8100 feet!) and by W2NAF (interesting operations in Antarctica, Svalbard and Virginia Tech). 

Ryan's New Prototyping Board

https://miscdotgeek.com/a-new-prototyping-pcb-for-qrp-homebrew-radio/

The Story of OSCAR 1, The First Ham Satellite

 

https://www.inverse.com/science/60-oscar-1-presaged-the-cubesat-era

Hack-a-Day: Has DIY become Click-and-Buy?

https://hackaday.com/2021/12/11/has-diy-become-click-and-buy/

Hack-A-Day today asks about the boundaries between DIY construction and the use of purchased, completed electronic components.   This is closely related to our long-standing discussion of what really constitutes "homebrew." 

Is it really homebrew if you buy a bunch of  already-stuffed PC boards and connect them together?  

Is it really a homebrew receiver if 90% of the components are inside one chip? 

Is it really homebrew if most of the signal processing is done in your computer (that you definitely did not build)? 

The comments below the article are interesting.  There we see some of the same arguments used by ham radio operators who are more inclined toward click-and-buy. They argue that since none of us are making our own resistors and transistors, we are ALL therefore click-and-buy people, so we should just get over it and pull out the credit cards. Some commenters carry this to extremes and ask if the real homebrewers are out there mining the copper for their wires.  

The debate seems to spill over into the software area:  One person asks if it is really DIY if you are using software libraries that contain code written by someone else.  Or to be truly DIY should you write all of your own code in assembly language?    

There is one very insightful comment about hams who are inclined to disparage the homebrewing that they did in their youth.  We often hear this:  "Oh, I used to build my own gear, but now-a-days I just buy commercial transceivers -- they are so much better."  As if homebrewing was a folly of youth, something that they grew out of (and up from) as they became able to afford the latest ham radio appliances.  As if homebreweing were a regrettable thing that was done only out of necessity.   This is, I think, sad.  

I think I'm a lot closer to the traditional concept of DIY than I am to click-and-buy.  I still prefer LC oscillators to Si5351/Arduino combos.  I prefer traditional filter rigs to SDR rigs.  And I prefer to make my own crystal filters.  I don't like to use ICs unless I really understand what is going on inside them (so I can be comfortable with an NE602 or an LM386, but I'm not comfortable with a CPU chip that may have millions of transistors in it).  But I am not homebrewing my own transistors nor am I mining copper. 

What do you folks think about this? 

https://hackaday.com/2021/12/11/has-diy-become-click-and-buy/

The Lamakaan Annual Radio Convention Starts Today!

 

The Lamakaan Amateur Radio Club's annual convention begins today in Hyderabad, India.  This is Farhan's club so it is sure to be a great event.  Presentations are being live streamed on YouTube and on the QO100 geostationary satellite. 

Here is the link to the convention: http://www.larc.in/larc4/

Pete N6QW will be the first presenter and will talk about his new PSSST Rig. He will be speaking at 0430 UTC Saturday 11 December.  That is 11:30 pm on Friday, December 10 on the East Coast of North America.  

I will be speaking at 1130 UTC on Sunday December 12.  That is 0630 Saturday 11 December EST. I'll be talking about the Mythbuster rig and about the ET-2. 

Here is the schedule.  

Here's a time zone converter: https://www.timeanddate.com/worldclock/converter.html?iso=20211211T043000&p1=505&p2=250&p3=137

Here is the Lamakaan Club's YouTube Live Channel.  https://www.youtube.com/watch?v=cRznKwGgvDo

I don't know how we might be able to watch or listen via the QO100 satellite.  The U.S. is not in the footprint of this bird.  But there is a good WEBSDR receiver run by BATC and AMSAT DL: https://eshail.batc.org.uk/

Where is Sunspot Cycle 25?

The other day I was complaining to Pete N6QW that 17 meters still seems to be in very poor shape.  I can hear 6Y6Y around mid day, but I don't often hear Europeans.  I did year my friend Mike EI0CL yesterday on 17, but conditions were not good.  Pete asked, "Where is Cycle 25?"  Good question. The Space Weather Center has the answer.  

Their Solar Cycle Progression page is up-to-date.  With the slider below each chart you can go back as far as 1750.  Check out Cycle 19.  I was born near the peak (TRGHS).  Pete was on the air during that cycle. Cycle 23 also looked pretty good. I was out in the Azores then (2000-2003) -- no wonder I could work VK and ZL with a 5 watt DSB rig.  

I like the little solar conditions widget that has appeared in the left hand column of this page, and I am grateful to the provider,  but the widget just doesn't update regularly.  So I think I'm going to switch to a link from the Space Weather Prediction Center that shows the numbers we really need: Solar Flux Index (SFI), Sunspot Number (SN), A index, K index.  (Please let me know what you think about this change.) 

Here is the link to the Solar Cycle Progression Charts (be sure to use the sliders):  

https://www.swpc.noaa.gov/products/solar-cycle-progression

Bluetooth, Winston Churchill, The Speed of Light, and a 1938 Zenith Receiver

 

Hello Bill -

It has taken me a while to put hands on keyboard to send you this message, but having seen or heard a few more of your references to Jean Shepherd, I felt I must. Being a fan of vintage radio equipment and the American scene of the late 1930s, sometime back I acquired a very nice circa 1938 Zenith 5-S-119 AM/Shortwave radio. 

Example: https://radioattic.com/item.htm?radio=1640094

Though it had been recently re-capped, it took some effort to get the thing working (needed a new power transformer), and still needs to be aligned, but it made a nice addition to my 1930s NYC Art Deco-inspired office. One reason I bought it was to add a Bluetooth receiver to it so I could listen to podcasts, etc, from my phone. I like the big electromagnetic speaker that those radios have and thought it would be cool to bring this one back to life. I picked up a small Bluetooth receiver board and a power supply for a few dollars online and got it working in the Zenith with no difficulty, except for some AC hum and oscillator noise that I will work on when I have time. So, success!

But here is the Jean Shepherd part. I recall one of his broadcasts in which he offered his theory that every radio transmission ever made is still out there, traveling further and further into intergalactic space and getting weaker and weaker, but still there. What an idea that was. I would say he is right. I have pondered the idea ever since. So being also a Winston Churchill fan, what would be the first recording I would play through the Bluetooth? What else but his 1940 blood, toil, tears, and sweat speech! So there was the scene — the Churchill speech playing the same audio waveform through a radio that might very well have played it live (or close to live) back in 1940! Almost (though not quite) like detecting the original still-traveling radio signal out there past the star Phi2 Ceti or wherever it is now!

Well that was a quick adventure this past summer that I thought you might appreciate.

Keep the Solder Smoke podcasts coming!

Tom Fuhrman, WX2J

Barrie Gilbert and Tinkering, Surplus, and the Visceral Experience of Electronics

 

Barrie Gilbert, 1951

From https://www.edn.com/analog-back-to-the-future-part-two/  :

"Gilbert believes that childhood hardships—including at age three losing his father in World War II, leaving his mother and three other children penniless—force one to be resourceful. Before and during his teenage years, he had access to a plethora of inexpensive military surplus gear which greatly helped to make him inventive. Gilbert laments that today's aspiring engineers are lacking the visceral experience of handling and hefting large coils and tuning capacitors, transformers and vacuum tubes, and such. Today’s surplus circuit boards are all but useless as a source of inspiration, or even “spare parts” to tinker with."

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

A really wonderful autobiography by Barrie Gilbert starts on page 7 of this page: https://hephaestusaudio.com/media/2009/06/the-gears-of-genius.pdf