Dave Platt wrote:

This looks like it would require 40 to 43 dB of gain to get to the level
that he needs for output.

Does anyone have suggestions of places to look on the web for application
notes and/or schematics for amplifiers along these lines?

I have done some searching on Google and found a few things but most of
them
take inputs of 30dBm or so and only take that level up to 40dBm. He still
needs to bridge the gap from 0 dBm to 30 dBm in that instance.

Hmmm. Seems to me that many of the VFO-and-mixer QRP CW/SSB
transmitter projects might have suitable designs... a few milliwatts
out of the mixer and bandpass filter, into a one- or two-gain-stage
driver which would then push power out to the final transistor(s).

Let's see. The Small Wonder Labs PSK-20 transmitters seem like a good
place to start looking. The schematic shows that the transmit
circuitry uses a Minicircuits TUF-1 mixer. According to the
Minicircuits web page, this takes as input a +7 dBm local oscillator
and up to 1 dBm of RF. It has a conversion loss in the 7-8 dBm range,
so you'd end up with somewhere around -6 dBm at most coming out of it.
The PSK-20 transmitter buffers this through a transistor, then through
a MAR-35M monolithic amplifier, and then through a 2SC1970 and
2SC1971, and ends up with 2.5 watts of power.

Seems to me that you could probably fiddle with this final stage a bit
(double up on the 2SC1971, heatsink 'em, run at a higher current
level, and adjust the driver circuitry to suit) and end up with 10
watts out.


Thanks for the information. I will check it out and pass it on to the
persons that were looking for it.

Al Butler
ka0ies