Stray RF in the Shack

RF getting loose in your shack is a common problem. Especially with high power, multi antennas and cables into the shack and cunning USB devices that do not have a lot of protection from the myriad of wires shielded and unshielded that weave around the back of the operating desk. I operate two setups on the desk and two amplifiers. You can see the setup on and as it only prevalent on 80/40 (trap dipole) and 30M (full size loop) I decided to stop living with the problem and do something about it.

The symptoms included, drop out of USB device from radio to computer (only on one radio/amp at some times) I also had keyboard lockup and experienced a fair sized buzz from one of the two speakers in time with any CW sent out from the Quadra amp. The Tokyo HP amp didn’t do it. My rotator control box would suddenly move the needle and the compass lights would flash with CW. The whole experience with a KW up the spout was quite exciting. It was also damned annoying!

The first thing most hams do is to buy a bunch of ferrite cores and snap on devices and load up the cables one by one. I did that and quickly ran out of ferrite devices and money with minimal improvement. Not much, but some. The most noticeable improvement came when I put ferrite on the rotator cable from outside as it was picking up RF from the LF antennas and bringing it into the shack.

I then decided to ground the whole station. RF grounding is something I never had had to do in 60 years of ham radio. Usually, the shields of coax cable tied everything together and that was grounded back to the mains power supply. Obviously it wasn’t working for me. A bit of research on the net pointed out that grounding doesn’t work if you “chain” one piece of equipment to another which is what coax cables do.

I went to the local electrical wholesaler and bought a brass bussbar with 12 slots and a small roll of #12 stranded wire and proceeded to wire each individual unit to the common bussbar. I also ran ground leads from the AC input filter to the station and from all the antenna switches. Oh yes, also the computer, and the speaker cabinet.

The result wa that it all worked as it should. No problems with any combination of radios, amps or antennas. The only problem that remained was the keyboard which still continued to lock up! I replaced it with another and it did the same thing. A few weeks later I mentioned the problem to another ham also involved with I.T He asked if the keyboard was a good quality one with a metal chassis or a cheap one that’s all plastic and suggested a HP keyboard as they have a metal chassis and a great quality build. I bought one and have never experience keyboard lockup since. I bought several more for our contest group ZM4T as they just feel good to use. The USB to Serial cable into the Maxtor CT17 for the Icom works fine now without any protection.

That’s was my experience. I solved the original problem and have since have removed over half the ferrite snap-ons. Maybe some of these ideas will help you with your RF problems.

73, Lee ZL2AL

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