Hello Stefan, LF
I can not overemphasize the possible need to keep the feedline "clean" and free
of RFI that may otherwise make it's way to any active whip antenna.
My first attempts at deploying the PA0RDT Mini-Whip here were unsuccessful and
disappointing due to the fact that some of the RFI I tried to avoid was
conducted from the shack out to the antenna along the coax. This may among
other things depend on what kind of radio the antenna is connected to.
If in doubt, my advice is to use one common mode choke where the coax leaves the
house and to ground the coax braid just behind it using an independent
earth-stake and then further a second common-mode choke just before the
feedline goes vertically up to the antenna.
For common mode chokes I use large high-mu ferrite rings that can take 20 turns
of RG-58 or up to 45 turns of RG-174 but smaller rings can be used with RG-174.
There is a picture here of the first test-choke I used for tracking down my
noise: http://peditio.net/utility/Attachments/choke_sml.jpg
This may be "overkill" in most installations but I'm sure some users can gain
from these extra measures just as I did.
BR
Paul-Henrik, OH1LSQ
|
