Just to add a comment on this thread:
I do not use an inductor to match my inverted 'L', just a capacitor from coax
centre/bottom of wire to the radial point. Further I do not use big wide space
'toast-rack' Cs, but tiny ceramic ones rated at 6.3KV which will handle very
decent amounts of power and are readily available over here. They seem to
handle the high currents at the bottom of the quarter wave 'L' quite happily.
I measure the impedance at resonance of the antenna without any matching
network, then use
www.sandiego.edu/~ekim/e194rfs01/jwmatcher2.html
to calculate the L-network values needed. Fit the parallel capacitor then
lengthen the antenna slightly to bring it back to the required frequency. This
provides the inductance necessary for the L-network.
Needless to say, your MFJ, or Palstar ZM-30 in my case, antenna analyser will
probably give you the wrong sign for the reactive part of the antenna's
impedance. This had me going for a long time before I realised the problem!
Check this by moving the analyser frequency LF from resonance and the impedance
should show -jX (capacitive). Moving the analyser HF from resonance should show
inductive reactance (+jX).
My inverted 'L' needs 1600pF to give me 50 + j0.
I have also made switched L-networks to successfully resonate the same antenna
on some other bands.
73
Tom G3OLB
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Topband Reflector
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