[TenTec] Audio Hum on Omni-VII

[Jim Brown K9YC]

On Thu, 18 Sep 2008 19:46:25 -0500, Dudley Hurry wrote:

>Could be, but not in all occasions..   Example, the Jupiter's audio 
>output is isolated ground,  audio ground is not chassis ground,  
>therefore you can not bond the audio ground to chassis ground,  
>isolation or matching transformers is the only way to make a good 
audio 
>connection.

Dudley,

What you describe is a classic pin 1 problem, which is well known as a 
CAUSE of Hum, Buzz, and RF interference. That doesn't surprise me -- 
nearly all ham gear is built with pin 1 problems, including my 
FT1000MP, my new K3, and my Omni V. The mechanisms by which this 
coupling occurs are VERY well known in the pro audio world, and are 
well documented in the tutorials on my website. The pin 1 problem 
first published by Neil Muncy, ex-W3WJE, in 1994, in the June 1995 
Journal of Audio Engineering Society. It is in any engineering library 
(visit your local university) and can be purchased for a nominal sum 
from www.aes.org. This is a peer-reviewed publication. You don't get 
published until some serious engineering talent has agreed that it is 
solid. Mr. Muncy was made a Fellow of the AES, largely on the strength 
of this work. 

Pin 1 problems are excited by CURRENT, which is in turn caused by the 
voltage difference between one equipment chassis and another. This 
voltage difference ALSO shows up in series with the signal because the 
interconnection is unbalanced. The bonding techniques outlined in my 
Ham Interfacing presentation, and in the RFI tutorial, reduce this 
current to a very small value by reducing that voltage to a very small 
value. The result is no hum, no buzz, using nothing more than plain, 
ordinary, copper wire. It is nothing more than a very simple 
application of Ohm's Law. 

No transformers are required. There is no "matching" to be done. 

73,

Jim Brown K9YC