{"id":4328,"date":"2021-12-28T10:07:00","date_gmt":"2021-12-27T23:07:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2021\/12\/28\/how-to-fix-the-spur-problem-in-my-17-meter-ssb-transmitter\/"},"modified":"2025-07-22T18:04:05","modified_gmt":"2025-07-22T08:04:05","slug":"how-to-fix-the-spur-problem-in-my-17-meter-ssb-transmitter","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2021\/12\/28\/how-to-fix-the-spur-problem-in-my-17-meter-ssb-transmitter\/","title":{"rendered":"How to Fix the Spur Problem in my 17 Meter SSB Transmitter?"},"content":{"rendered":"

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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<\/a> <\/b>(The smaller box is a Barebones Superhet receiver set up for 17 meters.) <\/b><\/p>\n

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. <\/b><\/p>\n

Important note: This is really just a problem with the “netting” or “spotting” procedure — the problematic spur does not<\/u> 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. <\/b><\/p>\n

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. <\/b><\/p>\n

I recently took a fresh look at it. Exactly which frequencies were causing the unwanted signals that appeared in my receiver? <\/b><\/p>\n

I used an Excel Spread sheet to find the culprits. <\/b><\/p>\n<\/p>\n

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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. <\/b><\/div>\n

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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: <\/b><\/div>\n
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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! <\/b><\/div>\n
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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. <\/b><\/div>\n

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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: <\/b><\/div>\n

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How would you folks knock down that 10th harmonic? <\/div>\n

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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 … Continue reading “How to Fix the Spur Problem in my 17 Meter SSB Transmitter?”<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":4329,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[44,292,94,60,17,23,25],"tags":[],"class_list":["post-4328","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-17-meters","category-dx-40","category-emrfd","category-hayward-wes","category-sprat","category-ssb","category-troubleshooting"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4328","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=4328"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4328\/revisions"}],"predecessor-version":[{"id":4333,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4328\/revisions\/4333"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/4329"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=4328"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=4328"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=4328"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}