On Fri, 10 Sep 2004 17:14:40 -0400, George Allgood wrote:
> My OMNI VI+ with computer wired to the Key jack swamps when
>I strike a key on the keyboard. The problem goes away if I reduce
>power on the OMNI to about one half.
I would be willing to bet that you have a simple pin 1 problem. In
case you have missed my previous rantings on the subject, the
problem is that the cable shield for the keying line is not getting
connected straight to the chassis on either end, but is going to the
circuit board first. In this condition, any RF current induced on the
shield will flow on the circuit board, and the voltage drop across the
inductance of the circuit trace shows up in the electronics.
The fix is VERY simple. At the Omni, connect the shield of the keying
line to the chassis, NOT to the RCA connector (which, on my Omni V
and Omni A goes to the circuit board, not to the chassis). At the
computer, connect the shield to the shell of the D-connector.
It also helps to use twisted pair for the keying line. The best twisted
pair is shielded CAT5. Connect one side of the pair to the keying
line at both ends, one side to the chassis at both ends, and connect
the shield to the chassis at both ends.
Second best twisted pair is braid-shielded cable made by Belden
and Gepco for digital audio. I have tested all of the cables and wiring
configurations in my shack on my K2/100 being keyed by my IBM
T22, with an end fed antenna that puts a LOT of RF in my shack on
all bands from 160M through 10M. Before I went to the cables and
wirings described, the computer would stop with a solid key-down at
above about 12 watts output. Changing to the wiring and shielded
CAT5 completely eliminates problems on ALL bands. The braid
shielded cable fixes everything but 10 and 15 meters.
The difference in cable construction affects signal coupled onto the
signal pair (the key line). The wiring on each end affects signal
coupled onto the circuit board "ground" trace. Two separate
problems.
Jim Brown K9YC
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|