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

[Lou Mecseri]

A bright "moon light" can keep solar panels generating  solar power.

73, Lou KE1F

On 6/9/2022 20:09, Alan Bloom wrote:
> Mystery solved!  The spurs appear to be coming from a solar 
> installation on a house about 1/2 mile (3/4 km) from my house.
>
> One interesting point is that the spurs do not go away at sundown, but 
> continue until fairly late in the evening.  Apparently that solar 
> installation must have some kind of battery to store the energy.
>
> Solar panels are DC devices and do not themselves generate 
> interference.  Rather it is the inverter(s) and other electronics that 
> are the problem.  There are two kinds of solar systems -- the ones 
> with all the panels in series feeding a single inverter and the kind 
> with a separate inverter for each panel.  The latter is the kind I had 
> on my house in California before it was destroyed in a fire and I 
> never had a noise problem.  I have heard that the single-inverter 
> systems are more troublesome from an RFI standpoint.  There was an 
> article in April 2016 QST magazine about how to mitigate RFI from 
> solar systems.  ("Can Solar Power and Ham Radio Coexist?" by Tony 
> Brock-Fisher K1KP)
>
> ------------------------------
>
> The story:  I finally go around to walking around the neighborhood 
> with my KX2.  I only have the AX1 antenna for it, which is not 
> resonant on the 40 meter band, and I was not using a counterpoise so I 
> could barely hear the signal from in front of my house.
>
> I started walking south down the street but the signal seemed to be 
> getting weaker.  So I turned around and walked north.  The signal was 
> getting slightly stronger the farther I went.  I turned right at the 
> end of the street onto another street and it kept gradually getting a 
> little stronger.  At one point I suspected it might be coming from a 
> Montessori school, but when I walked down the access street toward it 
> it didn't get any stronger.  Plus with everything in the news these 
> days I didn't think it would be a good idea for a strange man holding 
> a strange contraption to be walking around the school grounds.  :=)
>
> So I kept walking down the main street and within a couple blocks the 
> signal started to rapidly increase in strength.  It peaked in front of 
> a certain house, strongest at the right side of the house. Sure enough 
> there are solar panels on that side of the roof.  The signal was 
> peaking about S4 or S5 on the KX2 S-meter. Again, this is with a 
> non-resonant antenna with no counterpoise.
>
> As I mentioned, the spurs are about S6 on the ground-mounted trap 
> vertical at my house and they are almost buried in the noise when the 
> band opens up at night.  So I'm not going to bug the neighbor about 
> it.  But I bet they would have trouble trying to listen to AM radio at 
> their house.
>
> Alan N1AL
>
>
>
> On 6/7/22 17:21, Alan Bloom wrote:
>> 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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