[Lowfer] Strange QRM here on SAQ frequency

[Bill de Carle]

Bill, Graham, Jay...

The 120-KHz spikes seem to be pretty much symmetrical near 17 
Khz.  Something I didn't notice right away: there is a harmonic at 34 
Khz but nothing at 8.5 KHz or above 34 KHz, which seems strange.  On 
Saturday I drove around the neighborhood to see if I could pinpoint 
the source.  Used a netbook running SAQ-RX (1000-Hz filter centered 
on 17 Khz) with an e-probe sticking out the car window.  Too 
distracting to watch the LCD so I mostly drove while listening to the 
audio.  There is a 14.4 KV single-phase distribution line running 
along Rapid Road, serving about 200 customers (mainly cottagers at 
this time of year) until the road dead-ends about 7 Km (4.5 miles) 
north of here.  The QRM was strongest under that power line and 
diminished as I drove toward the end of the road.  Fortunately, the 
near-field falls off very quickly - just have to go 200 - 300 yards 
away from the main line and the signal drops below background noise 
level.  Interestingly, this also holds where there is a branch line 
running off at right-angles: no detectable signal even right under a 
branch line connected directly to the main line) as long as I was 300 
yards or more away from the main line!  Indicates to me that the 
signal is being generated all along that distribution line and its 
amplitude is a function of the current flowing at each point.  The 
signal also surges up and down as though responding to load 
changes.  I expect there is some threshold load below which no QRM is 
generated - got up later a couple of times in the middle of the night 
and checked: no detectable QRM, presumably because the total load was 
low enough.  I discovered that all the *main* 14.4 KV lines in this 
area radiate a similar signal and all the shorter branch lines do 
not.  Found one point at the intersection of Lookout Road and Lover's 
Lane where the amplitude was horrendous - the audio sounded different 
near that place, and looking at the display it was apparent the 
uppermost component was some 10 dB stronger (relative to the other 
components).  There is a small rooftop solar installation nearby 
which would no doubt be tied to the grid (part of Ontario's "Micro 
Fit" program where the province pays 80 cents a KWH for electricity 
they don't need, hi!).  Other than that, nothing unusual to account 
for the extra noise.  There is another somewhat larger solar 
installation just north of here right on Rapid Road but I did not 
detect any different-sounding or louder noise as I drove past that one.

So while I didn't pinpoint the specific source of my QRM, I did find 
out how easily it can be overcome: just get > 300 yards away from the 
power line!

73,
Bill VE2IQ

At 07:59 AM 7/7/2014, Bill, KU8H wrote:
>Hi,
>
>I'm late to post here because the example I have that sounds 
>identical to this is intermittent. On for a half second or so and 
>then back maybe 15 or 20 seconds later. Mine was an outdoor 
>electronic anti-mole device (that didn't discourage moles) in the 
>next door neighbors yard. Since it didn't discoutage moles and they 
>knew it caused radio interference the devices (two of them) went to 
>the landfill. With DSP I was able to copy CW signals that were in 
>between the 'horns' of those gizmos..supposed filter BW under 90 Hz.
>
>Good luck getting this sorted.
>
>73,
>
>Bill  KU8H
>
>On 07/06/2014 09:32 PM, Graham wrote:
>>Bill,
>>
>>Got to thinking some more on your strange RFI / EMI.
>>
>>I don't think I have ever heard the type of emi/rfi that an 
>>electric fence or invisible dog fence might generate so I have no 
>>point of reference with those.
>>
>>However, the types of emi/rfi that I do see are aside from furnaces 
>>and airconditioners and is on and off during the day is that from 
>>dimmer switches, outdoor sensored lights, hair dryers, and networks 
>>but they don't seem to bother me too much  and except for networks 
>>are short lived and are on and off fairly quickly. Network emi/rfi 
>>tends to be more HF.
>>
>>If what you have is on nearly all the time and is it possible that 
>>someone local has started to use a home network using broadband 
>>over power line?  I have never heard or am familiar with the 
>>spectrum of this this type of emi/rfi maker.
>>
>>In Embrun we have both smart power meters and remote reading water 
>>and gas meters. I think the water and gas meters use some sort of 
>>VHF frequency but have been unable to verify; I don't know about 
>>the "smart power meter" however.  I didn't notice any new emi/rfi 
>>suddenly appear when any of those devices were installed
>>
>>do let us know if you ever figure out the source of your strange QRM.
>>
>>
>>cheers, Graham ve3gtc
>>
>
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