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MOSFET IF Amplifier Circuit

MOSFET IF Amplifier Circuit

Three of these amplifiers are used in series to build the 455 kHz IF amplifier. AGC voltage comes from the AGC Circuit

The original inspiration for this IF strip came from the “Progressive Communications Receiver” in most of the recent ARRL Handbooks. That circuit is used at 9 MHz, uses two stages, and uses an LED (or two diodes in series) to raise the circuit ground of the MOSFETs. It is also a broadband circuit and could be used at any IF frequency given the limitation of the ferrite cores used. AGC performance falls with higher frequencies (10 MHz to 20 MHz), but works very well for 9MHz and below.

The Cadillac of all MOSFET IF strips is “A Universal MOSFET IF Amplifier”, by Georges Ricaud, and Doug DeMaw, QST, August 1981, Page 27. This circuit uses large red LED’s which on the author’s batch gave a 2.1 volt reference for the sources. He has two different AGC outputs, one that can be used at the RF amplifier or at the post mixer amplifier in this LED MOSFET receiver. The idea of using a 100 resistor in series at the drain was used in this receiver instead of swamping the output coil with a 2.2K resister like in the Progressive Communication Receiver. Ricaud’s circuit uses a series 100 ohm resistor at G1 as well as at the drain. This is a great idea for using the MOSFET at higher frequencies, i. e., like the 9 MHz that Ricaud’s circuit is designed. He uses a MC1350 AGC amplifier, which is needed for great AGC action at 9 MHz. You would want to use this circuit if you wanted to design a single conversion MOSFET receiver, instead of the dual conversion scheme of the LED MOSFET receiver.

Article by David White at http://www.pan-tex.net/usr/r/receivers/secifamp.htm

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