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Drake 2880

Good Morning to all,

Did some more Drake tests this morning that may be of interest.  I really
over analyzed the bias network in the .Drake converter.  When I drew out
the circuit I was convinced that  the circuit was providing a positive
voltage to the gate of the RF amp.  Indeed, with the device out the input
pad measures +5V.  That suggested all sorts of weird things to me, none
of which turned out to be true.  I decided to take Yoshi's advice and I
installed a device that I bought on ebay (it is an NE42484A Pseudomorphic
HJ FET - whatever that is) in my second fried unit and it works!  The
drain current is almost right on the 10 ma specified for the device.  Vds
is 3 volts instead of  2 volts specified for minimum noise figure at 12
ghz.  I need to change the drain resistor to get the Vds down a little
but the unit appears to be working OK.  I don't know how well yet (it is
better than the other one with the MAR-3 in the front end!).  "Finger
tuning"  around the front end circuits indicates the circuit is not
optimum for 2.4 Hz but the received signal level from the test source is
at least as strong as anything I have seen on the work bench so far.

It seems that there may be life after death for these units after all.

73 de Jess - W4MVB
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