[RFI] RFI Signature

[Jeff (W4DD)]

I added the pictures to the link.  Tnx.

 

Don, your comments so closely align with my thoughts it is almost like I wrote the comments.  I did think this was a PLN issue, and we cleared a major issue about .8 miles away, but that did not clear the issue.  We have run RFI Maper looking for PLN in the area many times but nothing of the right intensity shows up.  Have also done a lot of VHF investigation, but nothing conclusive.   This issue is actually in Rhode Island so I am not able to do it in person (I am in GA), but I have a couple of partners on site doing the leg work.

 

It is great to listen to the input of so many experts.  In addition to solving this issue, I am expanding my thought on RFI investigation.

 

More to come. 

 

From: Don Kirk <wd8dsb at gmail.com> 
Sent: Tuesday, November 25, 2025 8:10 PM
To: jim at audiosystemsgroup.com
Cc: Jeff (W4DD) <w4dd09 at gmail.com>; Rfi List <rfi at contesting.com>
Subject: Re: [RFI] RFI Signature

 

Hi Jeff,

 

Per Dave's (W0LEV) request I have attached 2 pictures.  One is the oscilloscope display of your noise which I called "RFI being investigated" when you were using 20 KHz bandwidth.  The other picture is using the same scope set up to view the audio from my SDR receiver of a known bad power pole that was typically arcing 2 times per each half cycle of the sine wave (again using 20 KHz bandwidth), and this was verified using a Radar Engineers Model 243 (typically 2 arcs per each half cycle).  You will see in my known bad power pole screen capture you have big peaks in the positive direction each half cycle of the sine wave where I'm not necessarily seeing that in your screen capture of your RFI being investigated (but it might be an optical illusion based on the 60 Hz sine wave I injected on channel 2 which is not necessarily in sync with the RFI being displayed on channel 1).  You will also see an odd gap in the positive peaking pattern on your RFI being investigated.  On channel 2 of the scope (blue trace) I injected a 60 Hz sine wave just to help visualize time relative to a 60 Hz sine wave and it's not necessarily in sync with the RFI being displayed but it helps visualize the time relative to a 60 hz sine wave.

 

I really have no idea what the RFI is that you are trying to find, and will let others draw conclusions (I never try and guess).  If it's somehow power line RFI and you are close to the source then you should also hear it up on 136 MHz as an example using a handheld beam turned to 136 MHz but even if it's not power line noise you might hear it on 136 MHz.  A perfect example is that last year I had a home 0.14 miles from my QTH that had a bad LED light fixture in the garage that was generating a lot of RFI on 160 and 80 meters and when I was in the street in front of this home I easily heard the same RFI up on 136 MHz and my 136 MHz DF gear pointed right at this house as did my HF DF gear.  Nowadays many things sound like power line noise so it's very confusing.  I use my family room LED light dimmer as a power line RFI generator simulator as an example.and depending on it's setting it looks and sounds just like power line noise arcing 1 time per each half cycle (and I hear it on HF and VHF) and it even interferes with our reception of a weak UHF over the air digital TV station.

 

Not sure if my pictures will get posted so you might add them to your folder for others to see if they do not get posted.

 

Don wd8dsb

 

On Tue, Nov 25, 2025 at 7:16 PM Jim Brown <jim at audiosystemsgroup.com <mailto:jim at audiosystemsgroup.com> > wrote:

On 11/25/2025 11:46 AM, Jeff (W4DD) wrote:
> I think the antenna is a StepIR vertical.  It seems to have a narrow BW.

I wouldn't expect it to be narrow on receive.

I'm not familiar with Flex rigs. Elecraft has very good RX bandpass 
filters on each band (or pairs of higher bands, and I would expect Flex 
to do the same.

Do you hear the noise on on other bands?

73, Jim K9YC





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