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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. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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