SB ALL @ ALLUSA < VE3MX $5284_VE3SNP
9600 baud UHF Mocom 35 Modification
R:910703/0418z @:W2OY.#WNY.NY.USA.NOAM #:11879 Z:14127 O:#5286 @VE3SNP
R:910702/2253 @:VE3SNP.#NIAG.ON.CAN.NA Welland Ontario #:5286 Z:L3B3A6

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 GREAT LAKES INTERNATIONAL DIGITAL ASSOCIATION, TECHNICAL BULLETIN ON
 MODIFYING THE MOTOROLA MOCOM 35 UHF SERIES FM TRANSCEIVER FOR 9600 BAUD PACKET
 by Ron Kramer VE3MX sysop GLIDA node stack Port Colborne, Ontario
 and asistant sysop of VE3SNP BBS Niagara Region. 

## NOTE.. Start with a operational tuned up radio on the frequency you are
          going to be using it on.

1. Remove DC power cord, Antenna cable, and take the radio out of the case.

2. From the component side of the radio, remove jumper from pin #40 and #41
   located with the front of the radio facing you just to the left of the
   center partition, about an inch and a half from the back.
   NOTE.. keep this jumper.

3. Remove the ends from the jumper in previous step. Obtain a 1.1 uH RFC
   and place insulating covers on leads, (note do not cut the leads on the
   rfc use full length), solder the jumper ends to the ends of the RFC.    

4. Install this RFC on Pins #40 and #3, note #3 is located to the right of
   T101 and the left of Variable resistor. on the left side of the radio.

5. Remove capacitor C119 to the right of T102.

6. Remove capacitor C117 to the right of T101.

7. Turn radio over front facing you solder side up.

8. On the right hand side locate T101 and T102 near the rear of the chassis.

9. Cut trace to the right of T101 alignment hole, between the first and second
   componet holes on trace going from front to back of set, (this trace has
   three component holes) see figure 1 below.


      - Add a 4 inch length of hookup wire here on top side of board to xtal
     :     ______________
     '- > : o           o:       _
          :o .-----------'      :o:3   
           -'         T101    .'.'    
                        _     :o:2 <-- add a 36 pf Mica here to ground   
                      ( 0 )   : : <-- cut here  
                        -     :o:1 <-- add a 47 pf Mica here to ground
                              '-'


                            Figure # 1


10. Solder a 47 pf Mica capacitor from hole 1 of foil you cut in step 9,
    to ground. See figure 1.

11. Solder a 36 pf Mica capacitor from hole 2 of foil you cut in step 9,
    to ground. See figure 1.











                                                           Page 2 of 3

12. See Figure 2 and cut trace to front right of T102 between hole 2 and 3
    of trace.

                        T102
                         _
     alignmnet hole -> ( o )
                         -    _ 3
                      _______:o:
 add 36 pf Mica -> .'  o _____.'
 here to gnd.    1 :o:'''' ^--Cut trace here
                   '-'  2

13. Connect power cord, antenna and turn on and retune T101 and T102 before
    continuing with modification, once tuned remove power cord and antenna.

14. Locate the Transmit Crystal channel element and remove from board.
    Open up the element and remove the fixed capicitor approximately
    25 to 32 pf that is in parrallel with the varialble capacitor.
    solder a 4 inch lenght of small hookup wire to the junction of the
    variable capacitor, crystal and thermisistor, on the foil side of
    this pc board. re-install the crystal circuit in the plastic 
    element case and file a notch on the side of the plastic case for
    the jumper wire to exit between the plastic cover and the main 
    chassis when reinstalled.

15. Reinstall the channel element on the main chassis.
    Solder the jumper wire from the crystal element to the rear hole
    where C117 was removed next to T101, (see figure 1). This is the
    is the junction of CR102 and R112.

16. Locate the mic jack on the left side of the chassis component side
    front facing you. There is a 10 pin terminal strip running along the 
    left side rail, number these terminals from front to back (1 to 10).

17. Disconnect the wire running from the mic connector to terminal strip
    pin 5. Solder this wire to blank terminal pin 7 on this strip.

18. Using a length of RG174 or teflon equiv. coax, prepare one end, and
    solder the center conductor to pin 7 of terminal strip on left side.
    Solder the shield to terminal 9 of same strip.

19. Feed this coax between the face plate and the pcboard near the speaker
    from the top to the bottom of the chassis.

20. Turn the radio over with the face toward you and the solder side up.
    Locate the metal shield in the shape of a trapizoid, near the front
    right side of the pc board (this shield has a 3/8 inch hole in it
    for alignment of the Discriminator).
    Along the front left angle side of this shield is a jumper wire 
    connecting the shield to the pcboard. Just to the rear along this
    side the very next foil trace is the discriminator output. There 
    is possibly a printed triangle with the number 15 pointing at this
    foil pattern. This is the junction of CR2, R35, C48, R37, R38.
    Using the Free end of the RG174 you just installed in step 18, 
    measrue and cut to length and prepare the end so that it can be
    soldered to the above described discriminator trace.
    Solder the center conductor to the trace described above and 
    solder the shield of the cable to the metal shield.

21. Connect the DC power cable and antenna to the radio, align the
    transmit crystal to frequency.




                                                           Page 3 of 3

22. Pin pinout of terminal strip on top left hand side is:
    front pin 1 - PTT
          pin 2 - Transmit audio
          pin 3 - ground
          pin 4 - ground
          pin 5 - wire from speaker
          pin 6 - unknown
          pin 7 - new discriminator output pin to mic connector
          pin 8 - jumpered to pin 10
          pin 9 - ground
          pin 10 - + 12 volt DC input to radio

23. Microphone connector 6 pin Din plug
          pin 1 - rx discriminator audio output to tnc
          pin 2 - ground
          pin 3 - ground
          pin 4 - 9600 baud tnc audio input to radio
          pin 5 - PTT line

         
24. That completes the modification. Hook up your 9600 baud PacComm
    Tiny 2 Tnc, set the tx audio level in the 9600 baud modem as per
    instructions from PacComm, and your away to Happy Packeting.

I hope that this Bulletin is of some help to other's working on System
development, more in this series will follow as modifications are made.
Next will be a writeup on the Mocom 70 series conversion which is very
simple because it is true FM to begin with, Also the Motorola Moxy, and 
the Motorola Maxar will be modified, these are also true FM.

73 for now and Happy Packeting from the Niagara Penninsula Ron VE3MX.
/EX