Sunday, December 7, 2008

A "go kit" for TVI and RFI?

What sort of things should I have an hand to solve RFI problems? I understand that it's risky installing devices on neighbor's equipment, but I would like to keep some things on hand to solve any problems I might have in my own house, and then can point to them and say "this solved my problem".

So far:
  • A FT-240-43 toroidal core, used to make a common-mode choke for feedlines. Wrap about 10 turns around the core: https://www.amidoncorp.com/skus/search?query=FT-240-43.
  • Having some snap-on cores might be helpful - although they aren't as effective as toroidal cores, they're really easy to install, so having a few of them might help identify which cable is the problem, and you could use a toroidal core then.
  • A high pass filter for 75-ohm CATV coax: http://www.mfjenterprises.com/Product.php?productid=MFJ-711B
  • A ferrite rod.
  • A low-pass filter on my station wouldn't hurt.
  • What about pickup from speaker lines? In the old days, you'd slap a capacitor across the speaker lines, but my ARRL RFI book suggests that modern audio amps won't like that.
Harris, K9RJ, pointed me to a great article written by Jim Brown, K9YC: A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

2 comments:

Anonymous said...

For speaker RFI usually the speaker wire is the antenna. I close wrap the speaker wire (there is almost always too much - one neighbor had enough for a 20 meter dipole!) over a ferrite rod. It works! In your own home keep the speaker wire as short as possible and use twisted pair (recommended by K9YC). Harris K9RJ

KM6I said...

Thanks, Harris. I'll add the ferrite rod to my list. And, I'm going to update my post with a pointer to Jim, K9YC's document, which I found on his web site: http://audiosystemsgroup.com/RFI-Ham.pdf