20M interrference

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  • Updated 12 months ago
Interference is noticed during the afternoons about 20Kc wide and 25 dbm in amplitude. 
Wipes out the digital portion of 20M and very slowly moves lower in frequency. 
Look familiar?

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Bill W2PKY

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Posted 12 months ago

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Mark - WS7M

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No idea but that looks rather nasty!
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David Ahrendts

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Bill, seeing similar anomalies when I began using the Flex display, I went on a big hunt for noise. I live in the middle of LA, so it could be anything from a neighbors bad light fixture to some big gun radar, aging arching power line, pool pump, etc. Doing some research I found the biggest cause for this type of roaming noise are switching power supplies -- those little wall wart plug ins. I systematically removed as many of them as possible from my station, added a centralized 12V DC noise-preventing power source (West Mountain Radio), replaced all zip line black-red wire with shielded twisted pair wire (noise cancelling), replaced all CAT6 with CAT 7 (shielded) cable, and re-checked all grounding. Helped immensely. Those traveling noise bumps disappeared. Interestingly, the biggest culprit was the wall wart for my LG display I was for the Flex 6500. I would have provided the shielded DC power to it, but the LG runs on an odd 24V, so it was replaced with a 12V DC Samsung which is dead quiet running off the shielded 12V supply. Another method to snoop for nearby noise is to find an HT that has AM aircraft band -- find a quiet frequency, squelch it to noise, put it in proximity to things. All of this also brought the general noise floor down to S3 rather than S6/7. Good luck.

David A., KK6DA, Los Angeles 
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Dan -- KC4GO

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I use my Kenwood TH-F6A with RX coverage from broadcast to 1.2 Gig.
With exception of the cellular bands. I recently purchased a SDRplay and will connecting it to my Surface Pro 4 and various antennas to locate the sources of interference.  
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Norm - W7CK

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David,

Would you mind elaborating a little more on the "replaced all zip line black-red wire with shielded twisted pair wire (noise cancelling)" wire you used.  Maybe a source, part number, website reference etc. 
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David Ahrendts

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Some people who have done considerable research into noise and wires suggest that the typical red-black zip line side-by-side wire invites noise. Twisted cable rejects noise (a lesson learned in the early days of telephone wiring), and shielded twisted pair is even better. I still use Anderson power poles, but with the twisted cable. Will get you the type/brand tonight.
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David Ahrendts

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Norm and all, for low amp-draw devices around the Flex, I use an 18AWG foil-shielded twisted pair speaker wire with the Anderson power poles (an Amazon purchase).
For the Flex itself, I obtained some very stiff 12AWG copper-shielded twisted pair that runs from the excellent PowerWerx SPS30DM (very quiet) power supply -- short 2-foot run.
For my UHF/VHF radios in the station, I do use zip line for the higher amp draw but noise is not the same issue for FM or digital in VHF/UHF.
Also, I forgot to mention the liberal use of ferrite clamp ons. Buy them in bulk. Put them on everything. Call me crazy but I even put small ones on both ends of the very shield CAT7 cables, certainly on all coax in and out, and certainly on microphone cables. Well, everything.
Excellent article above from Tim.
All of these steps truly reduced what I thought was urban-produced outside noise that was really with in feet of my Flex all along. Noise floor reduced from an irritating S5-7 to S3-4 and sometimes less. My two cents.