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HVAC RFI diagnosis, actions

Mar 4th 2020, 10:27


Joined: Feb 10th 2020, 08:12
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Total Posts: 0
I'm new to HF and due to the HOA rules, and on a recommendation from a couple of Elmers, I decided to start with a 20m dipole in my attic (in a 2 story house). The attic has a couple of gas water heaters and two gas HVAC heaters and blowers . After tuning the dipole I started listening on 20m and things seemed decent at first but then a 'white out' started which I tracked down to the HVAC systems running (individually or together). I'm not especially surprised but I'm wondering if I can mitigate this?

Here is the spectrum scope when HVAC isn't running:

Here is the scope once the fan starts running:

The units are about 3 years old so modern but are not the type that run in a low mode constantly. In addition to the white out type of noise there is sometimes a periodic noise as well. I can't tell an exact frequency spread on those but something along the lines of 15KHz. I checked other bands and some don't seem to be effected all and some only show a very minor amount of noise. I'm not sure if that is just the antenna tuning or if the emissions are close to 14MHz. SWR on other HF bands runs from 3:1 to 8:1 using this antenna.

I am aware of various 'stealth' approaches to HF, have read the ARRL book on wire antennas and so forth. It's an option I'm exploring. But at the moment I looking for comments on this RFI because one of my goals in putting up this antenna was to get some inexpensive lessons on HF in the real world. I've already learned a lot and this is just another useful learning for me to apply in the future. Thanks!
Mar 4th 2020, 14:55


Super Moderator

Joined: Apr 4th 1998, 00:00
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Mar 5th 2020, 06:30


Joined: Feb 10th 2020, 08:12
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Total Posts: 0
Thank you for the link. I had already reviewed Roger Hillson's presentation. It has an amazing amount of info, some of which is a bit advanced for me as a beginner. I didn't see the sort of noise I am observing mentioned there and was wondering if anyone had experience with something that looked like this and where they started in addressing it. Lacking that I guess my first step is to contact the company that maintains my systems and see if they can get involved with the manufacturer and go from there.
Aug 2nd 2021, 17:57


Joined: Jan 17th 2000, 00:00
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K5IDL de N6UG, Your scope images look very similar to my 40m band. I just installed a Carrier Mini-Split Ductless system and when the A/C is on, the noise wipes out the 40m band.

My installer has tried a couple of options but that has not fixed the issue. The installer is trying to setup a call with a technical resource at Carrier to discuss this more.

Hope you find a solution!


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