> His output impedance will be slightly above 3 kohms.
> So 300pf are plenty on 80m, also on 160m when his Q is not
> higher then 10 it
> will be fine as strays add to it.
Strays nomally subtract from the effective capacitance on
160. They add on higher bands, but the shunt reactance of
the choke dominatates on 160 and 80 reducing effective
capacitance....not that a Q of 8 makes much difference in
anything from what a Q of 12 would do.
> But with high impedance a higher Q will be needed for
> sufficient harmonic
> supression, so 500pf is the better choice.
> A padder of 500pf for 160m loading should be sufficient
> for proper loading
> from 25-150 ohms.
The biggest problem for higher harmonics is usually layout
or lead dress. You'd have to double Q or more to make any
worthwhile change in the lower harmonics. If the second
harmonic is an issue, better to make a series tuned trap out
of the padding capacitor. Then you can gain 20 dB or more of
additional suppression with no change in Q.
73 Tom
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