[RFI] Fwd: 20 Meter Interference

[K9MA]

Half a dozen or so turns of the wire from the wall wart to the device on 
a Radio Shack 2730104 "Snap-On" ferrite core completely eliminates the 
interference. These cores generic. MFJ used to sell them, too. According 
to the data sheet, 6 turns should be about 450 Ohms at 14 MHz.

73,
Scott K9MA

On 2/26/2021 12:04 PM, K9MA wrote:
> It turned out to be a wireless doorbell extender, right in the shack. 
> Once again proving that one should check your own home first. I'm not 
> sure if it's the wall wart or the device itself. It seems to have 
> magically fixed itself after power cycling, but I'm sure it will be back.
>
> I suspect the 1.1 second interval between noise pulses is the polling 
> period of the device, when it draws current from the wall wart. If a 
> ferrite core on the power lead doesn't fix it, I'll just unplug it 
> when operating.  Who wants to be disturbed by the doorbell then, anyway?
>
> 73,
>
> Scott K9MA
>
>
>
> -------- Forwarded Message --------
> Subject:     Re: [RFI] 20 Meter Interference
> Date:     Tue, 23 Feb 2021 20:25:09 -0600
> From:     K9MA <k9ma at sdellington.us>
> To:     rfi at contesting.com
>
>
>
> 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
>>
>

-- 
Scott  K9MA

k9ma at sdellington.us