Connect a 50 ohm 1 watt resistor from J102 center pin to ground on the
exciter PCBA. (This gives a load to the exciter in the receive, not
Pin 1 of P902 on the exciter PCBA is used for PTT. Connecting it to
regulated +10vdc, pin 8 causes it to transmit.
The RF output which can be anywhere from 50 mw to 150 mw is taken from
the exciter PCBA connector J101. (This is the output jack which is usually
connected to the PA)
Make sure that P902 pin 10 is connected to system ground.
Audio is injected into the channel guard input at P902 pin 9.
Tuning must begin at the oscillator level. The output from the oscillator
PCBA is located at J2 pin 5. The amount of drive at this point is critical
to the operation and successful tuning of the exciter. The signal here is in
the 50Mhz range and without enough the exciter will never tune correctly if
The oscillator module (FM Icom) has factory selected components to
accommodate the characteristics of the crystal that was installed. Replacing
the crystal may work fine and it may not. If you are having difficulties in
getting enough output from the oscillator PCBA or the frequency adjustment
seem difficult or effects the output level, try another module. Changing
capacitors in the module may or may not work.
It may be advisable to tack the crystal into the module, plug it into the
oscillator PCBA and measure the output. Try 3 or 4 modules and select the
one with the greatest output and ease of tuning.
Following the tuning instructions in the manual, use the following level
ranges for a guideline. Use a good quality analog meter, preferably a FET
VOM to minimize loading. Some meter deflections during tuning are very
subtle and a digital meter will not allow you to see them. If you don't
achieve the minimum at each stage, you will run into trouble. It is
important to watch the output of the exciter on a spectrum analyzer as
improper tuning will cause the exciter to run spurious.
|Metering jack J104 pin 1 from .5 to .8 volts
|Metering jack J104 pin 3 from .25 to 1.25 volts
|Metering jack J104 pin 4 from .4 to 1 volt
|Metering jack J103 pin 7 from .5 to 1.2 volts
|Metering jack J103 pin 6 from .8 to 1.8 volts
|Metering jack J103 pin 2 from .2 to .5 volts|