RFI - can anyone identify the source?

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  • Updated 10 months ago

I recently noticed unfamiliar source of RFI at my station.  The noise is most evident on 20m between 14.190-14.204 mhz. 

The sound generated by the RFI is ordinary/constant electrical static.  I have taken the following steps:  at the main circuit breaker panel, all power circuits were switched OFF.  Next, I turned on the AC circuit powering my current radio, IC-7300.  All other electrical circuits throughout the house were still powered OFF.  The RFI is still present when using only the single electrical circuit.

I initially discovered the RFI while using a 9 month old switching power supply, but the RFI still is present when the radio is powered from an Astron (linear) power supply.  I have Fios internet service at my qth: the RFI does not go away when the Fios ONT panel AC and battery backup power are powered off.  Another possible culprit was the outdoor street lamp located roughly 50’ from the radio.  I stood directly under the lamp holding a portable radio, tuned the radio to an used frequency: no noise/no RFI was detected from the street lamp.  Below image shows the radio tuned to 14.197 mhz and the visual pattern associated with the RFI.  I have one of the new 6400 series radios on order scheduled to arrive over next couple of weeks and would like to resolve this issue before the new radio arrives.  Thanks in advance for related thoughts!


 

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spinnaker

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Posted 10 months ago

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David Ahrendts

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My friend, it does not move, correct? Or breathe? Just a constant noise at this frequency, yes? Is it +20 over S9, or???
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spinnaker

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Hi David, I wanted to update you on the RFI issue.  Suddenly today I noticed that the mysterious signal formerly centered around 14.200 had shifted to around 14.240 mhz.  At this point, I reached out to my next door neighbor: as it happens, he recently acquired a new wireless router.  He agreed to run a test sometime later today where he will briefly turn the router off, then back on to determine if the router is the source of the RFI.  I speculate that this is a higher-end router that perhaps emits a stronger signal than the one it replaced.  If the router is configured to periodically change from one channel to another while searching for the quietest channel this would explain why the frequency changed over the past 24 hours.  I look forward to learning your thoughts.
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David Ahrendts

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Well that's worth testing. In my setup one of the RF nosiest devices is a 16-port D-Link switch. I upgraded all the CAT6 cables to shielded, grounded CAT7.
Another question: are you using two-conductor black and red Zip cable anywhere in your power supply to your rig? If so, you might swap that a twisted pair cable with good shielding.
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spinnaker

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Twisted pair is a good suggestion, but I doubt that is the issue here, because when I connected the power supply via a very short, 18 inch zip wire cable there was no change in the level of RFI.  On a related note, I recently reached out to a company that specializes in RFI mitigation.  They shared my view which is that source of my RFI is quite likely a faulty walwort used to power my neighbor's new router.  I hope to know more later today soon as my neighbor is available to perform the wifi router power down/power up test.
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David Ahrendts

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Maybe. However, typically that type of interference moves sometimes very slowly up and down the band in an upside-down U pattern while yours' is a real crisply defined buzz. That said, anything is worth a shot.
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spinnaker

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Thanks for asking.  The RFI is S6 (signal level on nearby unused frequencies is only S2).  It is just a constant noise...the signal does not shift in frequency.
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David Ahrendts

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So, not a switching power wall wart which would drift up and down. What does it sound like SSB, AM, FM? Is there content, or is it just a buzz or hiss?
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spinnaker

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There is no particular content, only a constant buzz that does not vary in amplitude.  The RFI is apparent irrespective of the particular mode of operation.  I do not see any way to upload a sample (audio) file to this forum but would be happy to send sample file via email.
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Steve - K6SRS

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You may find some good hints at this eHam link:
http://www.eham.net/ehamforum/smf/index.php?topic=71604.0
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David Ahrendts

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Steve has a good suggestion in the eham article. I think we could conclude this is a fixed device probably nearby but not at your locale. There is no time of day that it goes on or off? Is it worse at night vs. day? Etc.
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spinnaker

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Steve, thank you for the link!  I probably will build a simple loop antenna for use in combination with my portable sw receiver in hopes of narrowing down the general location of the RFI source.  I also agree with David's suggestion that the source must be nearby, but definitely emanating from somewhere outside of my house.  The RFI is present 24/7 and is always at the same constant signal level.  I walked around surrounding properties but could not pinpoint the source.  All local residential power lines are underground here; however, we do have overhead high tension power lines roughly 1/2 mile from this qth.  The power lines were erected around 2000 and so are of relatively recent construction.  My next step will be to drive closer to the power lines to see if perhaps the signal grows in intensity.
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David Salomon

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It's hard to tell from that screenshot, but it looks like a CODAR signal.  Does it sound like it's pulsating?  Look here: https://www.sigidwiki.com/wiki/Category:HF
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spinnaker

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Hi David.  As you appreciate, CODAR is "Coastal Ocean Dynamics Applications".  I am nowhere near the ocean, so CODAR presumably is not anywhere nearby.  I studied the image at sigidwiki.com.  The visual pattern is certainly similar to what I see on my radio.  However, unlike the pattern associated with CODAR, this particular RFI corresponds to a pattern that is continuous/non-segmented.
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spinnaker

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Here is a close-up shot showing the RFI in greater detail.

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David Ahrendts

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Another option is to use a hand-held set to the AM aviation band which is very reactive to any kind of RF interference. Or, yes, make something directional and see if it has a directional source. This is a device continuously on and fixed. Power company transformer?