Maybe it's not quite so simple, guys.
To be honest, I'm confused.
My first take would have been to tie the mic's "-" to the case ground.
Some of you have suggested that.
I'm suggesting that this is wrong.
One of our BCC contest stations attempted to use my ORION in the recent 160m
ARRL DX contest (SSB) but after 2 hours of failing to get their setup to
work with the ORION, they aborted the plan. They cut the 4-pin mic
connector off, soldered an 8-pin on, and used an FT-1000, Some of you may
be thinking that the hams there didn't know what they were doing, but if you
view their setup which they purpose-built on site just for the contest, and
consider the fact that they set yet another new world record, then maybe
you'll believe me that these were first class hams.
The problem incurred was strong hum and very scratchy audio (when
transmitting).
I had the team forward their exact configuration to me (connection between
the heil headset, the IBM notebook - through an audio line isolator - and
into the front-panel mic jack). I forwarded the drawing to Ten-Tec.
The reply was that this has happened a few times before and been cured by
separating the mic's (-) from the case ground.
With that, I rest my case.
73
Rick
<SNIP>
As to internal grounding, microphone connections and RF, I suspect that
radiation back into the associated equipment or cables is the culprit.
Grounding won't solve it unless one is at the electrical end of a 1/4 wave
or 3/4 wave ground pole. As to inserting a transformer, this is simply a
frequency limiting device (it won't pass RF) so the RF induced into the mike
cable won't get into the rig. I don't advise this approach as impedance
matching, common mode rejection, and associated humm pickup may prevail.
73
Bob, K4TAX
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