On Thu, 23 Dec 2004 09:08:39 -0600, Duane A Calvin wrote:
>I definitely have RF in the shack due to close proximity of
>antennas, but do not have any problem with a TT 705 microphone.
Simple fix.
Connect the cable shield to the chassis ONLY. Connect mic hot wire
to the mic input. Connect the control wire to the control input.
If the mic cable has "returns" or "grounds" that are SEPARATE from
the shield, connect them to the so-called mic ground and control
ground respectively. If the mic "return" or "ground" in the cable
is already connected to the shield inside the mic, do NOT connect
it to the "mic ground".
Someone else said:
>Your new Orion is a highly sophisticated radio.
Yes.
>For proper
>operation you will need to provide a "DIRECT" RF ground. Heavy
>braided cable and solid copper bus bars are insufficient.
BS. The problem is improper wiring of the shield of the mic cable
(and maybe with other cable shields too). Fix that and you've
fixed the problem. See the next comment:
>My Orion shows 1/2 ohm resistance between the mic connector and
>the rear ground lug.
Which tells us that whatever you measured on the mic connector
isn't properly connected to the chassis! That ohmmeter only
measures DC resistance. That means there is a long circuit trace
and some hardware between the mic connector and the chassis. Now,
go to the ARRL Handbook and find the equation for the inductance
of a piece of wire equal to the lenght of the wire inside the
radio that connects that mic connector to the chassis, then
calculate the inductive reactance of that wire at your operating
frequency. The "RF in the shack" is flowing through that XL and
creating a voltage drop, and that RF is getting into your radio.
To fix you problem, you have to keep that current OUTSIDE the
radio, and the way to do that is to connect the cable shield TO
THE CHASSIS ONLY.
My shack is on the second floor, and my earth connection is to
four ground rods, the closest of which is 25 ft away. Most of my
antennas are dipoles, but I have a ton of RF in the shack when I
load one of my antennas as an end-fed long wire that ends in the
shack (on 80 and 160). I can run 600 watts into it without "RF in
the shack" problems -- BECAUSE I have my cable shields properly
connected to the equipment chassis.
Note -- I do not own an Orion, nor have I ever seen one or the
schematic for one.
Jim Brown K9YC
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