[RFI] 20 Meter Interference

Dave Cole dave at nk7z.net
Tue Feb 23 22:05:18 EST 2021

This URL may help:


It has a lot of information on location and IDing RFI.

73, and thanks,
Dave (NK7Z)
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 2/23/21 6:25 PM, K9MA wrote:
> The spectra images didn't come through, so here are the links:
> http://sdellington.us/hr/RFI/20m_K9MA.jpg 
> <http://sdellington.us/hr/RFI/20m_K9MA.jpg>
> http://sdellington.us/hr/RFI/20m1_K9MA.jpg 
> <http://sdellington.us/hr/RFI/20m1_K9MA.jpg>
> 73,
> Scott K9MA
> On 2/23/2021 7:46 PM, K9MA wrote:
>> I've recently started seeing this signal on 20 meters, probably local, 
>> as it is present late at night when the band is dead. It is a swept 
>> signal, typically starting at about 13.625, sweeping upward to a sharp 
>> cutoff at about 14.125. The total sweep seems to be about 500 kHz. The 
>> sweep slows down near the upper limit and seems to dwell there. Sweep 
>> repeats about once per second. It seems to be amplitude modulated 
>> during the sweep, so it shows up as a series of pulses on the 
>> waterfall display. While the frequency range seems fairly stable, it 
>> does move around a bit. I can't tell whether the frequency change is 
>> systematic or random.
>> In the attached images, the blue trace is the peak signal, accumulated 
>> over many sweeps. The yellow one is the actual signal, without 
>> averaging, which I caught near the upper end of the sweep. The 
>> waterfall shows the pulsed modulation. Resolution bandwidth is about 
>> 440 Hz.
>> Any idea what this might be?
>> 73,
>> Scott K9MA

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