GP300 VHF modification to 220 / 222 MHz!


Page is under construction...please QRX...

Software mods to go out of band are available at  www.batlabs.com.

A few notes in the meantime:  You will need to take some brass slugs from
UHF VCO coils and replace the VHF ferrite slugs with them.  Tweak them
down all the way inside the coils, and they will lock on 220.  Change the
3 low pass filter coils near the antenna from 7 turns to 3 turns and the 4
capacitors to 12 pf.  At this point you will have 1 watt output.
UPDATE- 2/26/03 - Removing C115 and putting it in place of C114 gives
2.2 watts output.  Leave all the other capacitors alone.

You will also need to modify the front end
module (still working on that - as of 1/21, it's down to 1 microvolt.)
UPDATE - 03/07/02 - I have removed all passive components from the input/output
Chebyshev filters in the RF module and replaced them with single tuned circuits.
Sensitivity is now about 0.4 microvolts, but front end noise is lower than it should
be, and the squelch is still tight even at a setting of 1.
You will also need to jumper around or modify the VCO low pass filter
on the receive side.

Deviation and power set do NOT work outside the
original calibration points, and may need to be set manually with component
changes. You will need to either buy or cut an antenna for 220.

 Deviation is weird - about
7 kc with no encode tone, and 5kc with PL encode.