Hi Peter,
Hal said:
> On Behalf Of Hal Kennedy
>
> Common mode chokes DO NOT belong between boxes on your desk. As Tom and
> others have said. The objective is to get them all at the same RF
> potential, not isolate them from one another so they can seek their own
> independent RF potential.
To which you replied:
>I do not agree with that statement generally, especially when there is no
> good RF ground connection next to the rigs or the shack.
> If for instance you are using an antenna coupler with a doublet and open
> feeder then it is best to leave that floating and block common mode
> currents
> to the rig by a choke, if none is already part of the coupler and taking
> over that job.
What everyone should always remember is if we block HF current from a
coaxial line to intentionally float a chassis, we elevate the voltage swing
of the chassis. This is true even inside a device like a tuner, and it is
one of the reasons moving a balun to a tuner input can actually make balance
worse...not better!
There is no logical or justifiable reason to have different cabinets and
chassis on the desk floating at different RF potentials, and this applies to
every piece of gear.
There is a large focus only on current, as if voltage and electric fields do
not even exist, even by experts. Yet strong electric fields can create as
many problems as currents. One of our bible books written on baluns and
ununs totally ignores voltage as an important aspect of balance and
unbalance. Because of that, it has errors in core behavior, and even has a
balun design that forces balanced feeders into severe unbalance! A friend
of mine had a commercial automatic tuner using that balun design, and he had
incurable RFI into his station. No amount of grounding or beads, or any
feedline length, allowed him to operate 75 meters.
We have to pay attention not only to current, but what we do with voltages.
One of the last things we ever want is cabinets and chassis on the desk at
different RF potentials. If a tuner has a hot chassis, the tuner or antenna
system needs repaired, and that repair might mean NOT doing what a book or
article tells us to do.
The real root of our problem is lack of good peer review in technical
publications and information.
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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