[RFI] New RFI Source

[K9MA]

Hi Mike,

The other copies (harmonics of 78 kHz) show exactly the same structure. 
I hear the signal only on 20 meters, across the whole band.  They 
certainly go beyond the band, but it's hard to tell how far due to 
antenna bandwidth.  Looking at the whole band, I'm actually seeing 
harmonics of 39 kHz, though the 78 kHz harmonics are stronger.

Looks like I'll be taking a walk this afternoon.

73,
Scott K9MA

On 7/31/2024 7:26 PM, Michael Carter wrote:
> Scott, do the spectral copies at 78 kHz intervals
> mimic the sideband structure shown in your K4
> screen capture?
>
> Over what frequency range can you see the
> spectral copies (limited by antenna bandwidth,
> I suppose)?
>
> The120 Hz spaced fine spectral lines in the
> main lobe suggest to me a 120 Hz square
> wave modulating an underlying 'carrier' signal.
> AC power line signal rectified
> in the power supply for the device and coupled
> into the 'clock' carrier and its harmonics?
>
> The more distant sidebands don't exhibit the
> fine 120 Hz structure of the main lobe.  That's
> what's puzzling me.
>
> I'll be very interested to see what your DF'ing
> leads to......
>
> 73,
> Mike, K8CN
> ------------------------------------------------------------------------
> *From:* K9MA <k9ma at sdellington.us>
> *Sent:* Wednesday, July 31, 2024 5:56 PM
> *To:* Michael Carter <Mike.Carter at unh.edu>; rfi at contesting.com 
> <rfi at contesting.com>
> *Subject:* Re: [RFI] New RFI Source
> CAUTION: This email originated from outside of the University System. 
> Do not click links or open attachments unless you recognize the sender 
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>
> The carriers within that main lobe appear to be 120 Hz apart, so 
> likely line related. They seem to vary in amplitude, but are very 
> stable in frequency.
>
> 73,
> Scott K9MA
>
>
> On 7/31/2024 4:28 PM, Michael Carter wrote:
>> Hi Scott,
>>
>> The sidebands are not typical of any SMPS I've
>> looked at spectrally.  The fine spectral structure
>> inside the main lobe suggest 60 Hz or 120 Hz
>> modulation of the nominal 'carrier', but the
>> sideband spacing of ~ 1 kHz from the main lobe
>> is odd.
>>
>> What do you see when you zoom into the
>> main lobe?  Can you guesstimate the
>> spacing of the strongest sidelobes
>> within that lump?
>>
>> 73,
>> Mike, K8CN
>> ------------------------------------------------------------------------
>> *From:* RFI <rfi-bounces+mike.carter=unh.edu at contesting.com> 
>> <mailto:rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf of 
>> K9MA <k9ma at sdellington.us> <mailto:k9ma at sdellington.us>
>> *Sent:* Wednesday, July 31, 2024 5:08 PM
>> *To:* rfi at contesting.com <mailto:rfi at contesting.com> 
>> <rfi at contesting.com> <mailto:rfi at contesting.com>
>> *Subject:* [RFI] New RFI Source
>> CAUTION: This email originated from outside of the University System. 
>> Do not click links or open attachments unless you recognize the 
>> sender and know the content is safe.
>>
>>
>> This RFI source has appeared recently:
>>
>> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsdellington.us%2Fhr%2FRFI%2F24.07.31.png&data=05%7C02%7Cmike.carter%40unh.edu%7C5b47864c626340c4b55208dcb1a4e911%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638580569052206306%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=I3QbXdcat4zw3df8oU7lalFjpj9VCt3Qcf%2FvhKK3Hfs%3D&reserved=0 
>> <https://sdellington.us/hr/RFI/24.07.31.png>
>>
>> It appears to be harmonics of about 78 kHz. However, unlike most SMPS
>> RFI, it is very stable. It disappears at night, suggesting a solar
>> system, but it persists, weakly, an hour or so after sunset. Maybe a
>> solar system comm link, with a supercapacitor? However, I'm not aware of
>> any new solar systems nearby.  Anyone seen anything like this before?
>>
>> Needless to say, I'll be out tracking it soon.
>>
>> 73,
>>
>> --
>> Scott  K9MA
>>
>> k9ma at sdellington.us <mailto:k9ma at sdellington.us>
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>
>
> -- 
> Scott  K9MA
>
> k9ma at sdellington.us <mailto:k9ma at sdellington.us>


-- 
Scott  K9MA

k9ma at sdellington.us