[RFI] Common mode chockes

Pete Smith Pete Smith <n4zr@contesting.com>
Sat, 23 Oct 1999 18:56:08 +0100

In the course of troubleshooting my recent RFI problem, I discovered that
putting a large coax coil - roughly 15 turns, 6-in diameter, of RG8X - at
the shack end of my 75-ohm CATV feedline got rid of the last vestiges of
RFI to my wife's computer when the 80-meter array is pointed toward the
house.  The problem is that the addition totally changed the tuning of my
amplifier on 40 meters and up, due presumably to the added line length
transforming the impedance at the shack end to some new and creative values.

I'm now considering a commercial line isolator, in the hope that it will
control the common mode currents while not functioning (so much, anyway) as
a series transformer. First, am I correct in this, as a general assumption?
 Second, can anyone recommend a good commercial product that is effective
at 80-meters.  Third, could I homebrew an appropriate choke with 50 or so
#43 or #77 material beads on a length of teflon?  

73, Pete Smith N4ZR

Sometimes a tower is just a tower

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