[RFI] Investigating receive noise - got a few questions

Andy KU7T ku7t at ku7t.org
Thu Dec 20 19:24:54 EST 2018

Thanks for all the great advise and information. Here is an update and a follow up question:

I have identified these issues after a few weeks of research:

  *   (Small impact) My own ethernet switch/cable router created birdies around 14.03. Fixed with ferrites
  *   (large impact) My neighbor’s float charger for his truck and RV batteries caused sinus wave forms with the tips about 15 db above noise floor which wiped all weaker DX. The unit is a Schumacher Speed Charge, bought at Walmart.  Fixed by getting rid of and replacing with a different unit.
  *   (small impact) my neighbors ethernet switch creates similar birdies as mine did. Will fix with ferrites.
  *   (medium impact) my two Trane XL 15i heatpumps. When they run the create nasty spikes on 20 and 15, that are about 20kzh apart and about 5 – 10 db above noise floor. I want to fix this.

Regarding the last item on my list, my heatpumps Trane XL 15i (with electric auxiliary heat).  I have verified that it does not seem to be the inside blower, so moving my attention to the outside unit. I have taken a photo and would like to try putting a few ferrites in there at the indicated locations.


I could also put some preventive ferrites in the inside controller or maybe even in the thermostat. But I thought this is likely the source and if I prevent the noise to go out on the wires to the house, it may just fix it… Does this make sense?

Any other suggestions, before I open these up and try it?


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From: Andy KU7T<mailto:ku7t at ku7t.org>
Sent: Saturday, November 10, 2018 13:57
To: rfi at contesting.com<mailto:rfi at contesting.com>
Subject: Investigating receive noise - got a few questions

I am trying to sort out receive noise issues with my Flex.

I am not exactly sure how clean the spectrum could/should be. I have the feeling that I may be more concerned about this just because I can see the spectrum.  I am in an residenial area with 5 acre lots, with miles to the next town and businesses. I always throught/hoped I have no noise issues.

I took some time last night to turn off all breakers, one after another, until only the shack was left. Then I reduced everything in the shack so the only thing left was the 12V power supply, radio, computer and monitor.  I also adjusted the noise offset on the Alinco Powersupply with no changes, turned off the computer, and unplugged it. At this point any wall warts, modems, routers, etc were also  off. Still no significant changes.

Take a look here at my spectrum, recorded while I turned off a breaker every 30 s. There is no difference between beginning and the end: https://1drv.ms/v/s!AiAwh4TnZjYMhtoFCHwTeJdHO2MFGw

I really have not found any major decreases in hash or noise.  Here are my questions:

  1.  Do I go right about this at all?  Should I only look at the ham bands instead of looking at the half the HF spectrum?
  2.  There is quite some pulsing/jumping of noise going on below 10 Mhz (see in video’s top spectrum). Are those normal static atmospheric crashes or something else outside I should be investigating further and if so how?
  3.  There are patterns around 4 – 5 Mhz that are definitely some patterns from some device. Is it worth worrying about these, considering there are not near any ham bands of interest? Goes back to question 1 also: do I care whats outside of ham bands?
  4.  I have some harmonics, some spikes between 12 and 15 Mhz. the distance between the spikes is about 17.6khz. Any ideas what that could be? Is likely not in my house though…

Any tips and ideas how to proceed?


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