[RFI] 160m-5mhz noise?
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
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.
More information about the RFI