Giulio Scaroni wrote:
So i'm planning to made an Amrad antenna, i have send a request at
Crystalonics for high current FET.
Has anyone tried a small power MOSFET as input stage in an active
antenna? I am thinking of BS170, 2N7000 and similar transistors.
They have a very high forward transconductance (hundreds of mA/V)
and should make a very "stiff" source follower. They are easy to find
and are cheap too. The input capacitance is higher than that of J-FETs
(in the order of 30pF) but it can be compensated by a longer whip/wire.
The drain-gate capacitance is also high but I guess that a cascode
circuit can be used to minimise the effects of Mr Miller... Since they
are "enhancement mode FETs", they require some bias voltage to
start condicting but that's no problem. The big question is noise...?