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ICOM R8500 RECEIVER mk2 WORK IN PROGRESS ! The mixer is designed to frequency translate the IF output of the ICOM R8500 communications receiver with a stable L.O. signal of 80MHz to produce a signal in the VHF band. The idea being to 'view' TV signals tuned on the ICOM. According to the R8500 manufacturers manual I.F. output freq's from receiver are: Video carrier 16.2 MHz Audio carrier 10.7 MHz {output level -60dbm (with -50dbm input from antenna in WFM mode) also has +9 volt DC level} With a "high-side" Local Oscillator (L.O.) injection frequency of 80 MHz the expected output frequencies would be: Video carrier 80 - 16.2 = 63.8 MHz Audio carrier 80 - 10.7 = 69.3 MHz The frequency assignment for (Australia) Ch 2 is 63 - 70 MHz This RF signal can be "tuned-in" using a conventional (analogue) TV receiver, channel selector #2. The circuitry is a self oscillating dual gate mosfet mixer. Varicap tuning is used on the drain circuit, which is tuned to the 2nd harmonic of the xtal. Additionally a variation in gate bias can be used to determine best operating point and hence best output from the circuit. Input is AC (capacitor) coupled; which blocks +9V DC level from gate of mosfet. VERO LAYOUT |