>Almost certainly, but it is difficult owing to the EHT. If you design the
>PI-L circuit correctly, it will act like a low pass filter so ought to never
>be high Z at VHF. This does mean you have to use VHF techniques even though
>the amplifier is at HF. Short ground paths, thick conductors and multiple
>capacitors (i.e. 1 good low value VHF type in parallel with the HF one)
>for the DC block would be a good idea. It is better to use an HF transistor
>that
By nature a filter will look like a high or low impedance to any signal
outside of its passband. That's how they work. Plot the return loss of
a filter and you will see. The return loss will be 20 dB or better (for
a good filter) in the passband, but will be minimal (less than a dB)
outside the passband. So regardless of all the VHF techniques you employ
to build the filter, it still will not look like a 50 Ohm load at VHF.
And regardless of wether or not the impedance of the filter is infinity
or 0 Ohms at VHF, the signal will still be reflected back into the tank
circuit.
I don't think your statement is accurate about it never looking like
high-Z.
There are no resistive components in an ideal filter and so where does
the energy outside of the passband go? It gets reflected back into the
circuit. This is why regardless of how good your filter design is, the
VHF energy will stay inside your tank circuit. In fact, the better the
techniques are that you use, the more you are ensuring that the VHF
energy will NOT get passed outside the amp!
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@webspun.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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