[Elecraft] I need a Sherlock Holmes (weird spurs on 40m)

[Alan Bloom]

The weird thing about these spurs is how clean and stable they are. 
Switching power supply noise is generally not frequency-stable and it is 
not a clean CW carrier.  This one is actually TWO clean carriers, 
separated by about 150 Hz.

Alan N1AL


On 6/7/22 17:43, Fred Jensen wrote:
> I did the "Main Breaker 2-Step" and nothing went away.  My noise on 80 
> and 40 on the K3/P3 is highly varied ...
>
> 1.  Narrow discrete carriers [that appear linked, 25-35 kHz apart] 
> come and go, sometimes within seconds
>
> 2.  Broad [5-10 kHz] bands of noise, often without any harmonic 
> brethren [that I can find] that come in pulses that look like 
> wide-band AMTOR
>
> 3. "Rope-like" noise on the WF, with and without harmonic brethren 
> that often changes in character but mainly a primary signal 
> oscillating back and forth in frequency over maybe 5 kHz.
>
> Underground utilities, but we do have a 345 kV transmission line about 
> two miles away that runs from a large power plant 5 or 6 miles east to 
> somewhere up in OR near the Columbia.  Sources are a mystery, but I've 
> suspected harmonics of transmission line carrier-current signaling ... 
> they really look like sometimes it's just idling, and then a burst of 
> information.
>
> 73,
>
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
> Alan Bloom wrote on 6/7/2022 4:21 PM:
>> As part of christening my new QTH/antenna/rig here at N1AL, today I 
>> did the test where I recorded all off-the-air spurious signals on all 
>> bands and then threw the main circuit  breaker for the house and did 
>> the measurement again, powering the K4 from a battery.  This is to 
>> identify any spurs that are coming from my house so I can do further 
>> sleuthing to figure out what is causing them.
>>
>> One spur (or set of spurs) has me mystified.  It is a series of 
>> harmonics, with very stable frequencies, spaced at precisely 24 kHz, 
>> that extend from roughly 6.6 MHz to 7.4 MHz.  Each spur consists of a 
>> main carrier and a secondary carrier approximately 150 Hz lower in 
>> frequency and approximately 8 dB lower in amplitude.  The spurs are 
>> all the same amplitude, around -90 dBm (S6), dropping off as you 
>> approach 6.6 or 7.4 MHz.  I don't see these spurs on any other band.
>>
>> The spur amplitudes did not change when I turned off AC power, so it 
>> can't be the rig's switching power supply or any other electronic 
>> device in the house.  It's nothing internal to the radio because if I 
>> switch to a dummy antenna the spurs go away.
>>
>> So it's coming in through the antenna.  The antenna is a 6-band trap 
>> vertical about 30 feet from the house, with the coax coming 
>> underground to the shack.  We're on a large lot, there is a canyon 
>> (i.e. no houses) behind the property, and there is a vacant lot on 
>> the side where the antenna is located so the nearest houses in the 
>> neighborhood are about 150 feet away from the antenna.
>>
>> The electric utility power lines switch from overhead to underground 
>> at our property line, about 150 feet away from the antenna. Internet 
>> is via cable, which is underground also.  Both power and Internet 
>> enter at the far end of the main house, which is over 100 feet from 
>> the shack, located in a granny unit.
>>
>> I believe the exact fundamental frequency is 7007.03 kHz / 292 = 
>> 23.9967 kHz, in case that's a clue.
>>
>> Anyone have any ideas of what could be causing this?
>>
>> Alan N1AL
>
>
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