On 6/1/2014 11:01 AM, Bob McGraw - K4TAX wrote:
If one chooses to use only one Common Mode Choke or Line Isolator,
best first placed at the radio.
No, the first choke should be at the antenna feedpoint. W2AJI is exactly
right. A choke at the radio would only matter if the shield of coax
connector was not bonded to the chassis. So far, I've not seen a
transceiver where this mistake was made.
Now, an additional choke either at the radio or at some intermediate
point on the line CAN be useful to the extent that it functions as an
"egg insulator" for the common mode current induced on the line by a
nearby vertical antenna, which makes it a parasitic element of that
other antenna, modifying its pattern.
And there ain't no such thing as a 1:1 common mode choke. A common mode
choke is a straight through section of transmission line wound around a
ferrite core. No transformer action. No turns ratio.
In every radio I've looked at, the bodies are buried in the unbonded
unbalanced jacks, not on the output SO239.
73, Jim K9YC
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