>When I shorten my coil the antenna is resonant around 1.830 Mhz
(strange with 15+14.5 >meter) the swr value is something around 3+
from my MFJ analyser I measure around
>12-15 ohm on meter.
Rune, you need a bigger capacitor.
I think you're measuring the natural feed impedance of the vertical,
and your shunt capacitor is too small to do anything. 12 ohms
resistive in parallel with -252 ohms (350pF) is like 12-j0.5 ohms, and
that's what you're measuring.
.I think you actually need something like 3000 pF instead!!! The
shunt reactance needs to be somewhere around 25-30 ohms.
A 3000pF variable capacitor is probably not worth it... but you could
parallel a couple of doorknob capacitors with the shunt cap for fine
tuning, or you could use a shunt coil instead.
You only need 2.6 microhenries inductance for 30 ohms... this sounds a
lot like my shunt coil, and it's a 9 turns of #12 (2mm) wire about
50mm in diameter spaced over maybe 60-70mm .
You'll need to tap for slightly less inductance on the series coil.
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