Attached is my driver it goes between
VR1 and the outputs of T10 you need to remove C84 and T10 and
insert this circuit. I am using the AMP signal to reduce the
overall power output when driving a linear amp which needs 5W not
10W. U7 is a current driver, I chose it because I have a number of
them, I probably could select something better, or use an emitter
follower but it should do the job at 0 cost for me. The same with
the T13-1 transformer, I have them. The opamp was selected for its
speed slew rate voltage and current drive capability. C45 is there
because U7 needs a minimum load capacitance for stability. I will
see if I need to add something there later. TX is the switched 12
volts that is there in transmit only.
I am working on a PCB with this being one part of a daughter board
for the uBitx. I would be interested in any feedback. I am not
suggesting that this is a cost effective way of improving the
uBitx for production. I will post the entire schematic in a few
days.
Howard
On 6/8/2018 11:50 PM, Jerry Gaffke via Groups.Io wrote:
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And if you really
wanted an MMIC for the pre-driver,
here's a cheap one capable of 18dBm.? $0.55 each if you get a
reel.
? ??
