[RFI] 160m-5mhz noise?

Paul Christensen w9ac at arrl.net
Thu Nov 5 18:27:05 PST 2009

> About 4-5 days ago I started noticing my noise floor on 160m,
> which had been around 4-5, is now running S9 to S9+10.
> I did see it stop for a couple of hours on the 2nd day,
> but now it's steady all day 24/7.

I had a similar issue last year.  The root cause was an imported "micro 
fridge" being used in a home about 200 ft away from me.  It emitted a very 
broad level of noise that raised the noise floor on all lower bands. 
However, don't make the mistake that this is the same device affecting you. 
There are hundreds, perhaps thousands of garbage-producing devices that emit 
similar characteristics -- many of them are appliances of some form since 
they (and their internal RFI-emitting circuitry) are exempt from FCC 
certification.  If you're looking for a new appliance of any kind, look for 
the CE label that is becoming familiar on the Samsung and LG brands. 
Unfortunately, as time moves on, we're going to be forced to live with more 
and more switch-mode technology around us.  My own home contains dozens of 
devices from the clothes washer to cell phone chargers to an unknown number 
of switch-mode wall warts for all kinds of devices.  It's become exhausting 
to manage it all.   Siting antennas away from your home and other houses has 
become more important now than ever.

Although the MFJ device you own is probably a good tool for locating 
electrical arcing noise, its no match for switch-mode sources.  Because 
switch-mode devices seem to affect the lower bands, I have come to rely on 
one indispensable tool to locate these noise sources:  A Palomar LA-1 loop 
antenna.  The tropical band plug-in loop covers the lower bands through 6 
MHz with razor-sharp directivity.  In the example I cited, I was able to 
locate the noise source right down to the corner of the house.  From a 
distance, I could not localize the point due to the distribution of noise 
onto the home electrical wiring network.  But as I got closer, the noise 
became stronger and the exact source location became easier to spot.

Another tool I use with the LA-1 is an SDR-IQ receiver connected to my 
netbook PC and Elecraft K3's I.F. port.  The SDR-IQ functions as a spectrum 
analyzer on the netbook PC -- and its powered by the netbook USB port.  A 
14.4VDC gel cel powers the K3.  I just throw it all into a Klein 
electricians bag and start roaming on foot.  What's cool is that I can 
document and save the noise display on the netbook PC as I walk around my 
sample points.  This allows me to analyze it later, if needed.  Or, in one 
case, use it as evidence with a homeowner.  What I'm looking for is a sharp 
reduction in the spectrum display floor or switch-mode noise peaks as the 
loop antenna is rotated.  After moving to a few points, "X" marks the spot 
through triangulation.

In addition to a rise in noise floor, you'll often see switching peaks every 
30 kHz to perhaps 100 kHz, depending on the switching frequency of the 
source.  As others will point out, its wise to make sure your own house is 
clean before tackling the neighborhood.

No doubt a high-quality loop antenna can be home-brewed.  However, I have so 
many projects in the fire that I need to know when to just order something 
and the LA-1 has been an absolute blessing.  However, the LA-1 is no longer 
made by Palomar.  But the good news is that Palstar makes a near-identical 


The schematics are identical to the LA-1, but with a few improvements.  I 
just purchased their version of the tropical loop antenna since it resonates 
to 7500 kHz.  I have a new switch mode noise source only on 40m that the 
LA-1 loop cannot tune since it stops resonating at 6000 kHz.  So, I am 
hopeful the Palstar loop will stay part of my RFI/EMI detection kit.

Paul, W9AC 

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