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

[Alan Bloom]

That's the strange thing about this.  It doesn't have a grinding sound 
or anything other than a clean carrier.  Actually two carriers, the 
weaker one about 150 Hz lower than the main one.  That pretty much rules 
out any kind of switching power supply, for example.

Maybe tomorrow I'll take my KX2 pedestrian mobile and walk around the 
neighborhood to see if the signal level changes.

Alan N1AL




On 6/7/22 19:36, jerry wrote:
> On 40M I see noise every 15 kHz.  It's constant.  Sometimes stronger, 
> sometimes
> weaker, but it's always there.  The pattern is obvious on the 
> waterfall display.
> When I tune in one of the peaks, it sounds like a rhythmic grinding.
>
>                 - Jerry KF6VB
>
>
>
> On 2022-06-07 16:59, Alan Bloom wrote:
>> 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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