I believe, and I think most other shortwave listeners would agree, that the biggest problem facing our hobby today is noise, radio frequency interference (RFI) from other electronic devices.
Long Rambling Preface
Just sitting here typing on my wireless electronic keyboard, connected to a desktop PC, connected to two LED monitors, with a desk illuminated with an LED lamp, just to the right of a LCD weather station display, above a desk drawer containing an outlet strip with USB charging ports, sitting beside an AC adapter powering an 8-bay battery charger, wireless mouse, on top of a wireless PC speaker and an AC-powered Wi-Fi network extender, not to mention a smartphone, all within 3 feet of me, provides ample examples for potential for generation of RFI.
A few years back, I took three approaches to reduce the noise. I put a chair outdoors far away from the house with a 20 ft. wire up a tree antenna, I got an MLA-30+loop antenna installed at a far corner of the house with a shielded antenna lead in the window, and I went on an active search and destroy mission to find and eliminate the sources of the noise. That was because the first 2 approaches didn’t help.
The find and destroy approach had partial success. It discovered one particular device, a Nitecore D2 battery charger, that created more noise than everything else put together. It was beyond belief how bad it was, just plugged in, whether actively charging a battery or not. It saturated the whole house with noise so that the only way I could find it it was by singly turning off every breaker in the house, and once the offending circuit was found, I had to turn off and unplug every device and outlet strip until the noise stopped.
The other offending device was my electronic dog containment fence. It uses an Invisible Fence Boundary Plus® Dual Loop Transmitter to inject 10.7 kHz or 7.5 kHz signals into buried wires around the perimeter of my property. Those are high audio frequencies, not what we expect as radio. Nevertheless, the unit creates a raucous crackle on my radios everywhere between 4 and 6 MHz.
My radio listening routine has been to either drive somewhere away from home, or disconnect the dog fence and its battery backup, and then go outside. This has proven inconvenient particularly in cold or rainy weather and late at night.
Boundary Plus® Dual Loop Transmitter
This is what it looks like:
My understanding is that the box, upper left, is a lightning arrester (not sure what the 8 terminal connections are for as they’re not connected to anything). The wall wart provides 19V, 1A DC. Radio Systems Corporation is the manufacturer of Invisible Fence producgts.
That’s the dog fence. It’s FCC type certified (KE3-3002587) but that doesn’t seem to mean anything. Reading the net I find RFI problems with the Invisible Fence product, and others with no problem. I found one “solution” at eHam.net, installing a low pass filter between the “transmitter” and the underground wires that carry the 10.7 kHz signal. K7NA recommended a Corcom Model 10Vk6, but I had problems finding a new one, so I bought a similar product:
K7NA also said he put some ferrite cores around the power supply lines. I’ll do that too. I have a big bag of them.
I do not expect it to work because the last time I went down this rabbit hole, I unplugged the AC and ran the fence solely on its backup battery and while there was less noise in the house’s electrical wiring there was still plenty of noise directly from the unit until I disconnected battery too. My previous foray left me convinced that the boundary fence circuitry itself created all the noise.
But today when I disconnected all the power, there was still noise, suggesting that a new and perhaps even more powerful RFI source had sprung up. The strategy is now to seal up the dog fence, putting ferrite cores around the AC, a low pass filter around the underground wiring, and a copper taped shield around that whole apparatus and then continue search and destroy.
To Do
- Power off the Invisible Fence including battery backup, and then assess noise levels in the house. Try turning off each circuit and isolate there the noise is coming from. Remediate.
- Install the EMI filter on the Invisible Fence.
- Investigate whether a separate earth ground on the Invisible Fence makes any difference.
- Install ferrite cores covering the wall wart lead to the Invisible Fence.
- Construct metal shield over the Invisible Fence transmitter.