On Wed, 29 Dec 2004 10:32:47 -0500, Tom Rauch wrote:
>Chokes are only useful if ou have a low shunting impedance
>to ground, and they are most useful if the antenna or
>feedline common mode impedance is inductive (or the same
>reactance sign as the CM choke) at the point of insertion.
I would revise that to say that chokes are most effective and most
easily used if there is a low shunting impedance across the load.
Yes, I would love to have a low shunt Z across the load, but I'm not
going to throw up my hands if I can't -- I'll simply bring a bigger
elephant gun.
Example: I'm working on a problem whereby 850 MHz Nextel phones get
into the impedance converter stages of condenser mics via their
output wiring, mostly due to pin 1 problems inside the mics. A
single big #61 clamp-on (Fair-Rite 0461164281) looks like roughly
300 ohms at that frequency, and doesn't make much of a dent, but 3
or 4 of them does. That may sound awkward and expensive -- until you
happen to be working on a film shoot with some $3,000 mics that you
can't readily take apart to re-wire, and with crew and talent
costing upwards of $250K/hour.
I generally agree with your point re: the sign of the reactive
component, except that it matters a lot less if R is sufficiently
large.
Jim Brown K9YC
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