On 7/30/20 1:46 PM, Jim Brown wrote:
Hi Jim,
See comments inline.
On 7/30/2020 1:01 PM, jimlux wrote:
In an effort to keep the control and power wires to the remote tuner
from being "part of the antenna", I'm planning on choking it with a
cookbook design from Jim's book.
The question is, I would think I can take all the cables and run them
together through the cores as a "bundle" for this kind of thing. After
all, they're capacitively and inductively coupled by being in close
proximity, so from an "antenna" standpoint, it's one wire.
Yes. BUT -- an important design variable here is the parallel parasitic
capacitance in the equivalent circuit of the choke, which combines with
the inductance and resistance coupled from the core to "tune" the choke
to the frequency(ies) where suppression is needed. My "cookbook"
recommendations are based on measuring several specific cable types and
a specific winding style. Deviate too far from that and you're on your
own! :)
Yeah, that's sort of what I figured, say one had a bundle of wires (with
a shield) that is 0.405 inches in diameter (like RG-213), then choking
wise, it would be similar.
Also, better to have big chokes at carefully chosen locations (Where?)
or just put small choke at some interval of something like 5-10 ft.
Overall series impedance would be the same, but it's broken up.
The optimum locations for chokes are as close as possible to the noise
sources and to victim electronics.
I'm actually not so concerned about RFI -that's been dealt with by
design (and chokes at the source and victim) This question is more about
the cables winding up being a parasitic element of the antenna.
Think of the "breaking up guy wires with egg insulators" except that it
needs to carry signals, etc.
If my highest frequency of operation is 10m, then if I put a choke every
2-3 meters, then none of the "segments" between the chokes will be
resonant. (barring weird effects from self resonance across the choke).
An interesting experiment presents itself here..
If I have two antennas separated by 10 meters or so, and I measure the
S21 between them, and then I put a piece of wire of the right length
laying on the roof near them, I should be able to see it.
Then, if I put a choke in the wire, it should make it more or less
"invisible" at that frequency.
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