Hi Hal,
I'm not saying what you did didn't change something....but
the concept of common mode currents and isolators makes no
sense at all to me.
> Two remedies were proposed: That of a longer input
> coax cable and that of putting a line choke like the RF
> Works
> types.
The last thing any of us should do is place a common mode
choke on shielded cables between pieces of gear on the desk.
We want all the cabinets at the same RF potential, not at
different potential.
> My smaller amplifier, a manual-tune affair, had some input
> difficulty and this was because there was RF on the shield
> on a short cable.
How could that happen? Were the connectors not grounded to
the chassis on the amplifier? Was a shield connection in a
jumper broken?
Those are the only cases I can think of where the shield
could be excited by common mode in a properly configured
system.
If an antenna is way out of current balance on the feedline
terminals it would excite the outside of the shield and that
current might flow to the shack....but then it should come
to the entrance ground and virtually all stop. The common
ground buss should tie everything together. Even if it
follows a shield it should do no harm at all for stability.
It is on the OUTSIDE of the shield, and would never affect
SWR or RF performance of the rig or amp. Currents on the
shield can't change SWR inside the cable unless they somehow
change the termination impedance, and that can ONLY happen
with a radiating load like an antenna. They cannot change
signal performance unless they are getting into an interface
device like an audio line or power supply line.
>By using two 6-foot lengths, one on each
> side of a line choke I was able to achieve a better input
> match
> and reduce the RF feedback that was folding back the
> FT-1000.
How do you isolate the chassis of equipment in the same room
without creating RF in the shack problems?
73 Tom
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