I.F. OUTPUT MIXER FOR
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