Hello Pieter-Tjerk,
Thank you for your analysis.
The mini-whip works as a monopole vertial antenna, however contrary to a
normal monopole the gap is not at the bottom, but at the top. The result
is that the output is 6 dB higher as the effective height is the height of
the mini-whip and not height/2. However this is irrelevant as the output
is easily adjusted by adapting the size of PCB antenna.
The feed line is not part of the antenna. I have tested the use of proper
common mode chokes at different positions in the feed line. It did not
make any difference at all on received signal strength (Noise is a
different story, though.) I have also build a mini-whip fed with
unshielded CAT5 network cable with rf-isolating transformers at both ends.
This arrangement is preferred when grounding the shield of the coax at the
bottom of the mast to prevent noise on the shield traveling up to the
antenna, is not possible.
One test I still intend to do is to feed the antenna with a 9V battery and
use fiber optic to transport the rf to the shack. I am using a non
conductive fiber glass pole and my guess is that the antenna still will
work.
73,
Roelof bakker, pa0rdt
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