GE MVP Radio Mods by Bill Putney

			Instructions for Duplexing a G.E. MVP
				by Bill Putney
These instructions will work for MVP's on any band.
Before you start, test the radio completely to establish a 
benchmark for post conversion testing.  It is better to find any 
problems that exist in the basic radio and fix them now.  After the 
conversion you only need to find the problems you created.
MVP C.G. encoder/decoders are pretty useless after the radio has 
been duplexed so now is a good time to get rid of it.  Don't forget to 
replace the resistor between H1 and H2 on the System-Audio-Squelch 
board (The SAS Board).  Most of the duplexing is done on the SAS 

	1)	Remove the SAS board from the radio.

	2)	Cut the printed circuit land that connects J904 pin 2
		to U902 pin 7.  The best place I've found to do this   
is right near U902 pin 7 on the solder side of the    board.  
There is a land that goes from U902 pin 7 to a via pad.  
This trace is only about 1/8" long and is shown in gray in 
the MVP manual Outline Diagram.  I    use an Exacto knife 
to make these cuts.  Make two cuts perpendicular to the 
run of the land about 1/16" apart then remove the land in 
between by prying up one end   and pealing the copper 
away.  This disconnects the      receiver oscillator 
control line so that the U902 no longer can turn the 
oscillator off during transmit.

3)	Place a jumper between J904 pin 1 and pin 2.  I do    
that right at J904 on the solder side of the board.   This 
puts regulated 10V back to the receiver osc. control line 
so that the oscillator is always enabled.

4)	The next cut is a little harder to find.  The line on
the schematic that connects the junction of CR901,    
U902 pin 6, and J906 pin 5 to the junction of R905, R906 
CR905, C906 and U901 pin 7.  On the schematic it's a nice 
straight vertical line just above U902 but on the board it 
runs all over the place in and out of via's, from the solder 
side to the component side and back again.  The place I 
cut it is on the component side of the board near J905.  
Set the SAS board on the bench with the component side 
up and the board  oriented as shown in the MVP Manual 
Outline Diagram. On the Outline diagram you can see two 
component side lands that run parallel along the bottom 
edge of the  board the whole length of J905.  The bottom 
most land connects H16 to J906 pin 4.  Don't cut this 
one...    The one you want is the next one up.  It kind of 
looks like and S on the board and runs between J906 pin 5   
and a via just below U902 (next to H5).  I make the   cut 
near the end (pin 7 end) of J905 before it makes a turn 
and goes up toward U902.  Make the cut as described 
in 2) above.

5)	All of the I/O lines to the radio can be found on the
SAS board and should be connected before you put the 
board back in the radio.
PTT is at H17.  This is a ground to transmit line.
COS is at J912.  This line is ~0.1V when the radio is 
squelched and ~9.0V unsquelched.  Don't try to run a relay 
from this COS line.  I'd use a CMOS gate to buffer it.  If 
you're useing a modern controller chances are that it 
uses COMS logic and the buffer isn't required.
Mike in is at J913.  This line has mic bias on it and 
should be capacitor isolated.  It takes about 2V P-P to 
drive the radio to 4.5 Khz deviation.
Receiver audio is found at H16.  This is unprocessed 
audio.  It is not squelch gated and is not de-        
emphasized. There is ~4V P-P with 4 Khz deviation on  an 
on frequency signal applied to the receiver.  This should 
not be loaded by less than a 10K input.

6)	Put the SAS board back into the radio.

7)	Unscrew and unsolder the SO-239 antenna connector 
and remove it.  (If this is a UHF radio I'd throw it away and 
get an N connector but it's up to you).  After the conversion 
this will be the transmit antenna connector.

8)	Unsolder and disconnect the coaxial jumper at H2 
on the Filter board.  Disconnect P1 (this is the antenna 
relay control and can be cut off and pulled out of the 
harness or left alone.  It won't do much when you're 

9)	Remove the filter board from the radio.

10)	Using solder wick remove as much solder from 
around the antenna relay can on the component side of the 
board as possible.  Also use solder wick to remove as 
much solder as possible from the relay pins on the 
solder side of the board.  If you can remove enough 
solder from around the pins you can break them lose 
with a small screwdriver of knife when the solder is 
cold.  This will make the relay easier to remove. With 
a small pair of diagonal cutters grab a corner of the 
relay can.  Using the soldering iron, heat        whatever 
is stuck and remove the relay.

11)	Now you need to remake the connection between the
output filter and the antenna connector.  I use a piece 
of center conductor from a piece of RG-58 to do this in 
the hopes that the dielectric and the conductor 
diameter will keep the impedance about right.  This 
jumper should be placed as close as
possible to the circuit board in the holes left by pin 4 and pin 7 
of the relay.

12)	Now you need to rig up an antenna connector for the
connector on the front end casting to the antenna 
connector.  This means no voids in the shield around the 
connectors at each end.  If there are unshielded parts of 
this assembly the receiver will hear the transmitter 
and the resulting desense will be unacceptable.  
Use a good quality connector like a BCN or TNC (or type 
N if you can make it fit...).  I like all of the connectors 
to come out the back of the     radio.  This is real handy 
from the point of view of  working on the radio later 
and looks real nice but is a pain to do.
If you chose to do this (or put an accessory connector on 
the back panel of the radio) you need to take all the 
boards out of the radio and mask off the back of the 
radio from the rest with newspaper and masking tape to 
keep drill filings from  getting into every nook in the 
sheet metal and causing problems later.  
Mount the connector as close to the edge of the cover 
opening as you can or it will hit the filter board when 
you put it back in.  Make sure whatever connector and 
coaxial you use for this will make the turn to miss the 
filter can.  You could mount all this stuff on the front 
(plastic panel) and save yourself a lot of work but it 
wouldn't look as nice and it only takes time to do it 

	13)	If you choose to put an accessory connector on the
back panel I suggest you put it near all the other 
connectors.  To make room for this you will need to 
remove the little sheet metal doodad G.E. decided to 
put on the back of the radio.  Don't forget to mask off 
the power connector especially around the base where 
it meets the back panel of the radio.  Metal filings like 
this way of getting into the radio.  
The doodad is held by two spot welds.If you look 
carefully you can see where they are.  Drill these down 
to the point where the drill is just getting into the 
back panel.  Be careful not to screw up the power 
connector in the process.  
I put the accessory connector next to the power       
connector.  I like 9 pin D type connectors.  They are 
widely available and of good quality.  The D shape    
makes them a pain to mount without a punch (the       
Greenlee punch for this is >$280.00).  Get the        
connector as close to the edge of the cover cutout as 
you can.  This keeps it up high in the exciter area   and 
out of the way.  You are working through two      layers 
of sheet metal so be careful when (if) you tap the 
mounting holes as the tap tends to bind between   the 
layers.  Put the radio all back together now.

	14)	Put the output filter board back in and solder the
transmitter antenna connector back to the tab on the 
filter board.

	15)	Retest the radio to make sure it survived 
the operation.

That's all it takes to make a $100-$200 MVP nearly as 
good a duplexed radio as a $1,000-$2,000 MSTR II base