On Fri, 23 Jul 2004 11:14:02 -0400, Bill Tippett wrote:
>It's ridiculous that we have two manufacturers
>recommending two different connection schemes for such a simple thing
>as a microphone/PTT connection.
Yes, it certainly is. But the reason may be a failure of some to understand and
appreciate
"the pin 1 problem" -- that is, the mis-termination of shields within
equipment. Lots of ham
gear, including most Ten Tec equipment, suffers from this design error.
The proper termination point for ALL shields is the shielding enclosure
(chassis), NEVER
the circuit board. When the shield goes to the circuit board first and then to
the chassis,
any RF current flowing on the shield (for example, due to antenna action) will
get into the
equipment and cause trouble. The mechanism is simple common impedance coupling
--
the path to the chassis through the circuit board has inductance, and the
voltage drop
across that inductive reactance gets imposed on various points in the circuit
that are
dependent on layout of the circuit board.
Heil's advice to terminate the shield to the connector shell suggests an
awareness of this
important issue, and is a good step in the right direction. If this causes
problems with any
radio, including the Orion, I would suggest that there is a problem with the
radio.
Repeat after me -- "You call it a mic cable, but mother nature calls it an
ANTENNA."
(Quote attributable to Neil Muncy, ex-W3WJE).
Note that my comments are generic -- I own several pieces of Ten Tec gear, but
not an
Orion.
Jim Brown K9YC
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|