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More on DEMI 2400-144RX downconverter



More on the input impedance of the DEMI AO-40 downconverter...
My measured values of 5 to 6 dB return loss are correct.  I verified
these values using the old ARRL Radio Designer software.  Even though I
called DEMI on the phone and their answer was "50 ohms".
One thing I noted dorking with ARRL Radio Designer, which may be well
known to the group, but just in case...there is a wire inductor on the
LNA GaAsFET gate (input) for noise matching.  A significant noise figure
tuning capability with this LNA layout (which is identical to many of Al
Ward's fine published LNA designs) is in how the wire is formed against
the PCB.  Simple tuning on the ARD model showed around 0.3-0.4pF of
shunt capacitance right at the GaAsFET gate can improve the input NF by
several tenths of a dB.  When you're in the 1.0dB NF range a few tenths
make a BIG difference in sensitivity!
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