On 8/22/2013 10:03 AM, Charlie Gallo wrote:
One odd thing I found - every keyboard around the house (and I have different
brands from cheap to Unicomp Model M keyboards) has horrid RFI_IF_ you are
close to it (like the hand held within say 6-9 inches)
Most trash like this is radiated as a common mode signal by the cable --
in other words, the cable is a transmitting antenna. Before spending big
bucks on a new keyboard, I would try a suitable common mode choke on the
cable. "Suitable" means wound on a suppression core with the number of
turns that makes it resonant in the frequency range of the interference.
Bear in mind that the typical circuit Q of the resonance is on the order
of 0.4 to 1. Fair-Rite #31 is the weapon of choice below 5 MHz, and is
quite effective to about 200 MHz. Fair-Rite #43 is a bit better above 20
MHz, and quite effective down to about 5 MHz.
Some of the trash may be radiated by wiring within the keyboard itself,
and a common mode choke won't make a dent in that part of it.
73, Jim K9YC
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