800 to 900 MHz
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I haven't done one yet, but if you want to convert from 800 Mhz to 900 MHz, this is a place to check:

Instructions for modifying an 800 Mhz GE MASTR EXEC II Exciter to 900 Mhz

Copied from that site because it might be a dead link.   Thanks to http://web.archive.org/web/*/http://www.cdi2.com/build_it/900mhzma.htm

Replace C24 on the oscillator PCBA from 24pf to 18pf.

Replace the following components on the exciter PCBA.
C127 from 30pf to 22pf. C129 from 30pf to 22pf. C136 from 24pf to 18pf. C137 from 22pf to 15pf.


Replace C105 on the Audio Processor PCBA from .033uf to 1mf. (This is for a more linear audio response)

Cut 1/8 turn off of the top of the helical resonator coils Z101 & Z102 on the exciter PCBA.

If the exciter is used alone, i.e. without the receiver, the following will apply.

bulletConnect a 22 gauge wire from pin 8 of P902 on the exciter PCBA to regulated +10vdc.
bulletConnect 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 transmitting, mode.


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 at all.

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.


bulletMetering jack J104 pin 1 from .5 to .8 volts
bulletMetering jack J104 pin 3 from .25 to 1.25 volts
bulletMetering jack J104 pin 4 from .4 to 1 volt
bulletMetering jack J103 pin 7 from .5 to 1.2 volts
bulletMetering jack J103 pin 6 from .8 to 1.8 volts
bulletMetering jack J103 pin 2 from .2 to .5 volts


Except for portions owned by others, Copyright: Ray Vaughan, 2008