Iam using one of the C-3 Classic antennas by Force 12.
Performance on 14 Mhz is excellent, still Iam having some
abnormal values of SWR on 21 and 28 Mhz.
The ressonat point on 21 Mhz is at 21.080 Mhz and on 28Mhz
it stands on 28.700 Mhz, minimum SWR Iam able to achieve
on both bands is of 1.5 (1:1.5) SWR, which I think might
be a bit high.
I have assemble it with all instruction book measures, the
RF choke is 8 turns of 10''diameter of RG-213/U Mil, the
antenna stands at a height of 22 metres high and the Coax
from the RF Choke to the transceiver is RG-213/U Mil with
a lenght of 40 metres.
There is another variable that might influence the C-3, is
that I got a 3 element monoband Yagi for 7 Mhz stacked right
below the C-3, being the distance between both of 2,5 metres.
Could you please advice me about this abnormal SWR level at
the ressonant frequency on 21 and 28 Mhz ?
Could you also advice me on some soluctions to reduce at
maximum the interaction between both antennas ?
Some fellows here in Portugal also say that the position
of both 10-24 stainless machine screws that connect the coax
to the driver (active 20 metre element) is important to
optimize the SWR on the C-3 antenna.
They say that this screws must not be facing ground, but that
they must be 95 degrees displaced from that position !
Is this correct ? -Or just common sense !
Its all for now.
Your answer will be mostly apreciated.
Jose Emanuel Ribeiro de Sa CT1EEB
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