Andreas points to diagrams in the article (see below). The first (A) shows how the biologist might view the radio. The schematic (B) shows how engineers or technicians view it:
Category: troubleshooting
Repairing the Sony ICF SW1 Receiver — Used for Numbers Station Reception? Why no replacement for C-625?
Troubleshooting and Fixing Old Faults in my Long-Suffering Hammarlund HQ-100 (Part 2) (video)
WD-40, a Hard Drive, a Coat-Hanger Antenna, Dumpster Diving, and Amateur Radio Satellites from the Azores
Colin M1BUU’s Homebrew Manhattan SST
SolderSmoke Podcast #235 NE-602, Azores Rig, Spur Problems, SSB Rigs, Peashooter, HB Filters, MAILBAG
SolderSmoke Podcast #235 is available for download:
One contact on uBITX. More SW listening.
Repaired my Chrome Book in Santo Domingo!
Christmas Present for All: James Web Space Telescope launch
Exorcism Lite — Spur Suppressed on 17 meter Transmitter — Split TX/RX Station On The Air
2) Try putting a series LC shunt circuit tuned to 41 MHz at the output of the carrier oscillator (between the oscillator and the buffer).
3) Reduce the voltage to the oscillator/buffer. I have this on a pot, so I can adjust it down to the point where the remnant of the harmonic is no longer audible, while keeping the main carrier osc signal sufficiently strong.
It seemed to work. I could now hear the desired frequency for spotting, without the confusing tone from the spur.
Why had I been able to do this back in 2002 in the Azores using a simple trimmer cap to ground? My guess is that I was using my Drake 2-B as the receiver. The trimmer cap to ground may have reduced harmonic output. And I was probably cranking back the RF gain on the 2-B to the point where I could hear the desired signal but not the remnants of the spur. I have no RF gain control on the Barebones Barbados receiver that I am using in this project.
So, what’s the lesson from all this? Well, if you are faced with a serious technical problem, and you find yourself considering complicated and difficult solutions, go to the Dominican Republic for about a month (especially if it is January or February), and then take another look at the problem when you return. If you are unable to travel this far or for this long, taking a walk or taking a weekend break from a troublesome problem will likely have a similar mind-clearing effect.
The video above shows part of a February 1, 2022 QSO with Gar WA5FWC using the split TX/RX 17 meter rig. Gar is an amazing long-time SSB homebrewer who got his start with phasing rigs back in the day.
Exorcism Not Quite Complete — Thinking of Other Options
As often happens, I may have jumped the gun in declaring the exorcism of my 17 meter transmitter to be a success. As readers of this blog will recall, my problem was that when trying to “net” my separate 17 MHz receiver and transmitter, at around 18.116 MHz I could hear more than one tone as I tried to get to zero beat. The 8th harmonic of my 5.176 MHz carrier oscillator was mixing with the 23 MHz VXO signal and producing a spur. I could probably knock the level of this spur down below FCC limits, but — and here is the problem — I probably could never knock it down to the point that it would not be audible in the sensitive receiver that sits right next to the transmitter. So this is really a netting problem, not really a spur problem.
I don’t want to try another filter frequency — I have VXO crystals that really work only with a filter at 5.176 MHz.
So here is my current idea: Build a receiver board and turn this thing into a transceiver. Switch with relays the input and output of the 5.176 MHz filter, and use relays to switch to the receiver board the VXO and carrier oscillator signals.
Making this thing a transceiver would eliminate the need for netting. This should solve my problem.
What do you folks think?
73 Bill
Exorcism Completed! Getting Rid of the Spur in my 17 meter SSB Transmitter using a TinySA (video)
To re-cap: The problem became evident when trying to “net” or “spot” my transmitter onto my receive frequency. Around 18.116 MHz, I could hear at least two tones in the receiver as I moved the transmitter frequency. I needed to get rid of the extra tone.
First, thanks to all who sent in suggestions. They came in literally from around the world, and this is a demonstration of the IBEW in action. I used or at least tried all of them. They were all good ideas.
Following Vasily Ivananeko’s pseudonymous suggestion I rebuilt the carrier oscillator (apologies to G3YCC). I used the carrier oscillator/buffer circuit from Farhan’s BITX20.
Henk PA0EME said I should look at the signal level at the input ports of the NE602 mixer. Henk was right — the VXO input was far too high. I lowered it, but the problem persisted.
At first, I thought that the spur in question was so small that it would not show up on the air. I could not see it in the TX output using my TinySA spectrum analyzer. That was good news and bad news: Good that it was not showing up on the air, bad that I could not see it in the TinySA and use that image in the exorcism.
At first I thought that the spur was being caused by the 10th harmonic of the carrier oscillator and the third harmonic of the VXO. This seemed to fit. So, following VK3YE’s sage advice, I built a little 69 MHz series LC trap (using a coil sent by AA1TJ, on a board CNC’d by Pete N6QW). That trap succeeded spectacularly in crushing the 10 harmonic. Look at these before and after shots on the TinySA:
Spectacular right? But guess what? The problem was still there.
I scrutinized the situation once more. I realized that the spur would be more visible if I put the TinySA on the input of the transmitter’s PA (a JBOT amp designed by Farhan) as opposed to putting it on the output. Watching the spur and the needed signal move in the TinySA as I tuned the VXO, I realized that they were moving in opposite directions. This indicated that the spur was the result of a carrier oscillator harmonic MINUS a VXO-generated frequency (as the VXO frequency increased, the spur frequency decreased). Looking at my EXCEL spread sheet, I could see it: 8th harmonic of the carrier oscillator MINUS the main output of the VXO.
To confirm this, I plugged the values into W7ZOI’s Spurtune program. Yes, the spur popped up and moved as predicted.
For further confirmation I shut down the carrier oscillator by pulling the crystal from the socket, and then just clipped in a 5.176 MHz signal from my HP-8640B signal generator (thanks KB3SII and W2DAB). Boom! On the TinySA, the spur disappeared. Now I at least knew what the problem was: a harmonic from the carrier oscillator.
Following good troubleshooting practice, I turned off the gear and went to bed. When I woke up, an idea came to me: Before launching into a lot of filtering and shielding, just try running the carrier oscillator at a lower voltage, seeing if doing so might reduce the harmonic output. I disconnected the carrier oscillator board from the main supply and clipped in a variable voltage bench supply. Watching the signal on my TinySA, I watched as the spur completely disappeared as I reduced the voltage from around 13V to 10V (see video above). The main signal frequency level did not change much. I tested this by listening for the hated extra tones. They were gone. Exorcised.
Key lessons:
— Spur problems are difficult to troubleshoot. Armstrong’s superhet architecture is, of course, great, but this is definitely one of the pitfalls. Single conversion makes life easier. IF selection is very important. Choose wisely!
— When looking at the TinySA as you tune the rig, pay attention to which way the spur is moving. This provides an important clue regarding the combination of harmonic you are dealing with.
— The TinySA is a very useful tool. It seems like it is easier to use than the NanoVNA (which is also a fantastic tool).
— It can be fun and rewarding to re-visit old projects. In the years between original construction and the re-look, new test gear has become available, and the skill and experience of the builder has improved. So problems that once seemed insurmountable become fix-able.
— Thinking through a problem and thinking about possible solutions is very important. It pays to step away from the bench to think and rest. Rome wasn’t built in a day. Here’s a rough block diagram that I drew up (noodled!) while trying to figure out this problem:
Troubleshooting Apollo: 23 MHz Crystals in a NASA Ground Receiver
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.
Right to Repair Update
Allan WA9IRS sent me this article. Thanks Allan.
The French “repairability index” is an interesting concept. I wonder how modern ham radio “radios” would score. I think our homebrew rigs would max out the index.
Pete has commented on manufacturing processes that do (or don’t) factor in access for repair.
One of the recent horror stories we’ve heard is about a certain manufacturer of mobile phones. It seems that they have designed the phones so that if you dare to replace a broken screen, the new screen won’t work unless you de-solder the associated chip, then re-solder in the SAME CHIP.
Previous blog posts on this:
https://soldersmoke.blogspot.com/2010/11/knackers-of-world-unite-you-have.html
https://soldersmoke.blogspot.com/2021/03/mending-vs-ending-fight-against-planned.html
SETI, Proxima Centauri, The Parkes Dish, and Intermodulation Distortion?
A cosmically interesting troubleshoot. But I’m not sure about their explanation. Why would the intermod disappear when they moved the Parkes Radio Telescope off of Proxima Centauri?
No Longer On the “Shame Shelf” — Pete Fixes His KWM-1
Scott WA9WFA’s Mate for the Mighty Midget Receiver is WORKING! (Video)
The Perpetual Troubleshooter — John F. Rider — W2RID
The Joy of Fixing Broken Things (a really amazing video)
Mending vs. Ending — The Fight Against Planned Obsolescence
We don’t get a lot of mail from Darwin, Australia, so the message coming in from Phil VK8MC immediately got our attention. When I looked into the details I realized that it was very SolderSmoke-relevant. The Guardian article that Phil cited even mentions hobbyists tinkering with electronic devices in their sheds (that would be us!). Phil points to the connection between our repair efforts and the struggle to save the planet: “It’s not just a hobby, it’s an ethical position which contributes to the well being of the planet. A higher calling indeed!”
Here is the article Phil pointed us to:
The poster above (which hangs above my workbench) is from https://www.ifixit.com/Manifesto.
Repairing My Maplin Audio Waveform Generator
I picked this generator at the Kempton Park rally in London many years ago. I use it quite a bit, not only for circuit testing but also as an easy way to get my homebrew BITX rigs to send a signal so that I can adjust my antenna. I just plug this thing into the mic jack, crank in a small amount of 1 kHz audio, and I am ready to minimize SWR.
SolderSmoke Podcast #228
Of course, no travel. But vaccines are here so maybe soon we can leave our shacks.
In the meantime:
I’ve been playing chess against AI bots on chess.com.
Netflix recommendation: The Bureau. From France. A review from NPR:
A reading from “Conquering the Electron.” Germanium vs. Silicon.
Bill’s Bench:
The KLH Model Twenty-one II. Acoustical Suspension. First receiver WITH A PILLOW! Bad speaker? Blown AF amp finals. Hot heat sink. VBE Multiplier. Desitin.
Tony Fishpool’s recommended LM386 boards. 10 for 11 bucks. Nice. They work. Pictured in the Amazon ad at the upper right of the SolderSmoke blog page.
Putting a digital display on the Lafayette HA-600A
Test gear trouble. My Radio Shack multimeter getting flaky. I many need something better. Auto ranging? My beloved Maplin AF generator died – will have to fix. I need that thing. Probably a bad chip. Good thing they are socketed.
I almost forgot about SKN! But I remembered and I made one contact with the HT-37 and Drake 2-B.
Pete’s Bench:
Presentation to RSGB on Homebrew.
TenTek Troubleshoot.
Swan 240? Looking nice.
SDR adventures.
MAILBAG
Bill N8ET sent me some really nice Showa 9 MHz 8 pole crystal filters.
Kevin AA7YQ Smoke jumper! Building a hybrid SDR.HDR rig. Launched blog. FB
Nick M0NTV working on similar HDR/SDR project. Great video.
Grayson KJ7UM Hollow State Design – Launched a new blog. Very FB!
Thomas K4SWL of SWL Post blog. Kearsarge Mountain Transmission system. And recent events.
Peter VK2EMU Poetry. CW poetry.
Pete WB9FLW looking at DSB rigs…
Drew N7DA Feels not like a real ham because he hasn’t built a quad from bamboo. Which type of landscape bamboo is best for antennas?
Ryan Flowers of MiscDotGeek.Com blog is also watching the Tally Ho YouTube videos of Leo Sampson. Wants to put a WSPR beacon on the Tally Ho.
Joe KF5OWY Working with diode ring mixers, trying to see the mixer action on his ‘scope. 1 and -1!
Jim AB9CN sent a cool idea about how to do a 20/17 Moxon.
Roy GM4VKI – I thanked him for his article in SPRAT about putting a 2n3904 on the output of an NE602 10P mod. Brilliant.
Roger Hayward Told him that I really liked his Dad’s recent web site updates.
Farhan – Jokingly cursed me for showing him the Oscillodyne regen of Hugo Gernsback and Jean Shepherd. “Now I will have to build this!”















