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From: billp
Subject: G.E. MVP to a Repeater (Instructions)

Date: 29 Jul 92 17:29:57 GMT



I know nobody asked but I did this for someone else and I thought

it would be nice to share the information.  A lot of clubs these

days have a need for a new repeater and what with the economic

thing don't have a lot of money to spend.  There is a lot of junk

being marketed as ham repeaters (i.e. Spectrum Communications)

for horrendous prices.  I thought it would be nice for people to

have the choice to do the Ham thing and save a bunch of money.



These radios are available all over the place for very modest

prices and make great repeaters.  They work on our California

mountain tops without being fried by the other R.F. around.

Better yet they are a good neighbor.  They put out power on

just one frequency at a time and the receivers are selective

enough to work on 12.5 Khz split channels (though most Japanise

portable radios wont).  The transmitters are very clean if

tuned up according to G.E. instructions.  Transmitter tuning

only requires a wattmeter, dummy load and a VOM.  I have tuned

the receivers up with just a weak signal on channel but I do

recommend a signal generator.  The MVP's will put out ~60% of

it's rated power (there are several models ranging from 5-35

watts) continuous duty.  This isn't a lot of power but at

least when you add an power amp to it the amp won't be

multiplying garbage.



P.S.  No I don't work for a company that sells MVP's nor am

I interested in duplexing any more for other people.  I really

love these little puppies and I have them running all over the

place but I've done 20 or so and I'm not as young as I use

to be. :)



----------------------- Cut ? -------------------------------



                   Instructions for Duplexing a G.E. MVP

     by Bill Putney

  WB6RFW



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 board.



     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

           through).





     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

           receiver.  THE MOST IMPORTANT THING HERE IS TO HAVE A

           CABLE WITH A CONTINUOUS SHIELD from the receiver

           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 right.





     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 station!






SOURCE: The QRZ Windows Ham Radio CDROM



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