Many 160m receiving antennas have to assign the ground at the antenna feed
to the antenna to supply the current sink for the received signal on the
antenna. Certainly a beverage or BOG fits this description, as do others.
The common placement of the transformer I have seen for these types is at
the signal acceptance end of the antenna.
If the shack side feedline is also grounded "sufficiently" near the antenna
feed, then the natural resistance of ground becomes a common path to
transfer feedline common mode to the antenna on the far side of the
For these kind of RX antennas, the antenna end of the shackside feedline
shield needs to be isolated from *both* ground *and* the antenna side of the
transformer. Several devices for this isolation have already been posted in
this thread. A common mode choke on the shackside feedline 1/4 wave from the
transformer toward the shack will attenuate the tendency of a high Z
isolation at the transformer to form a common mode current node at that 1/4
wave point and make the shield less liable to accumulate noise current at
the operating frequency, further restricting common mode signal pickup.
This amounts to *two* common mode chokes though they may be implemented
Ground on the shackside shield should be somewhere on the shack side of
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