[TenTec] Re: Heil ProSet on Orion - reprise

Jim Brown jim at audiosystemsgroup.com
Fri Jul 23 11:35:45 EDT 2004


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  





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