[Elecraft] RFI issues

[David Ahrendts]

Andreas, TV transmitters at 500 MHz +- are really not noise disrupters in our amateur HF world. In fact, in our AREDN mesh work in LA, we’ve found that Ubiquiti sector antennas at 3 GHz and 5 GHz producing just milliwatts of power play nicely next to commercial TV transmitters generating 1.5-million watts at 500 MHz. So it’s something else.
A few years ago, I was on a similar RF noise hunt in my systems which reside in central LA, an RF noisy place. Some things I learned:
1) Pay close attention to how your power supply is connected. Use shielded twisted pair wiring from your power supply to your radio, and do not use red-black zip line. Unless twisted, that untwisted cable becomes an excellent antenna delivering noise to your system. In fact, pay attention to all cables. Make sure they are shielded. 
2) Hunt for noise makers. At that time I made the really dumb mistake of having two touch lamps near my radios — ya know, ya hit the base to raise or lower brightness. Those things will make noise for miles. Away they went.
3) Older plasma flat screens (pre-LCD) are noise makers. Most light dimmers. Someone even had a coffee maker with a loose heating coil connection that was through the roof with noise.
4) In my hunt for noise makers, I used an aircraft band hand-held receiver (that’s AM), squelch off, and just walk around touching the antenna to things.. Eye opening. Ya know what my biggest noise maker was near my radios?! My D-Link switch which lives under the desk not 3 feet from my HF radio. Further all of those CAT6 cables were great little antennas just spreading that noise all over. Solution: feed the switch highly filtered power and change all cables to CAT7 which is heavily shielded CAT6. Made a big difference.
5) Ferrite beads, clamp-ons. Get a bunch. Put them on every cable. Double up on the coax. Keep standing waves away. You want to discourage RF from traveling in places where it should not go. Ferrites are wonderful. Get 'em on Amazon.
6) Grounding. There are several well-known AC filtering devices that can add an extra ground to your AC mains coming into your radios.
7) Switching power supplies. Those wall-worts. Noisy beasts. Best to use a centralized, filtered 12V DC system that eliminates those wall worts altogether. One of the worst noise makers near my radios was a lovely, beautiful LG display which could not be plugged into my highly filtered and shielded 12V DC system because they run own 24V. Switched it out with a nice Samsung which runs on 12V and it runs totally quiet.
Good luck. The hunt may take a while But these steps took my urban noise from S7 to S1. Was worth the time.

David Ahrendts, KK6DA, Los Angeles