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Old September 30th 05, 03:30 AM
WSQT
 
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Grounded gate? Not too likely with the IRF 510. You will need 5V
drive at least, at all full current! Since a grounded gate(base, grid)
amp has only voltage gain, you would have a theoretical gain of maybe
3db at 12V, 6db@24V, and so on,but given unity gain from the IRF 510 at
12V grounded source at VHF, maybe unity or worse real world at VHF
regardless of supply voltage.

The IRF 510 has a maximum peak voltage of 100, thus a maximum safe
supply of around 34. Of course, a tube with several hundred volts
supply(or several KV for a big one) is quite another matter, as are
those 1KV peak MOSFETS as seen in some Class E 160M/80M rigs. No idea
what input C is in the latter, though.

Lastly, at grounded gate you still get the same voltage-variable
135pf gate-source C as your input C, you just get out of the Miller C,
which is an estimated 22pf times 2 for an MF/HF rig with 12V supply and
12V drive, or times 3.5 for a 30V supply. Input loss gets damned high
in this capacitance, and this is why a device that(grounded-source) at
MF has 30dB gain has 10dB gain at VHF.

 
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