Modifications to the Motorola Pulsar II Mobile Radio Telephone



The Pulsar II is a UHF (459 Mhz TX 454 Mhz RX) full-duplex FM radio.  The

following modifications will adapt it for use as a UHF repeater on the 70 cm

HAM band.  Our mod targeted Tx 448 MHz., Rx 443 MHz.



"Model D" refers to the Model T1839D family.

"Model A" refers to the model T1839A family.

 (T1839R,



Order the service manual through Motorola.  Cost $30, phone 1-800-422-4210

Model D manual - order part number 68P81047E60-O

Model A manual - order part number 68-81029E65



If you need to figure out what manual to order for some other model,

call Motorola Parts Identification at 708-576-7418.



In many places, we used a spectrum analyzer to measure RF signal strength.

A sensitive RF volt meter may be used as a substitute.  Or a high speed

Oscilliscope.





READ ALL INSTRUCTIONS (FROM BEGINNING TO END) BEFORE STARTING



UNTIL YOU ARE TOLD TO DO SO, DO NOT APPLY POWER TO THE RADIO



0) Remove these boards (you won't be needing them):Supervisory Logic,

Option, and Interface.  Remove phone number wiring from interconnect

 board.



1)  All models:

VCO range change.  Remove the Frequency Generation Unit by removing the

4 mounting bolts, 3 coax connectors, and wiring harness connector P107.

Remove the 8 bolts fastening the VCO side (there is only 1 side with 8 bolts).

Remove the side, taking care NOT to let the rubber feet pull the circuit

board out with it.  C6 (trimmer capacitor) is the mid-range VCO adjustment.

Visually set it to mid-range (plates at 90 degrees to each other).



  Apply ground to the FGU case, 10.2v to P107-1 and 4.0v to P107-7.  Add

capacitance in parallel with C6 (the variable capacitor) until the VCO is

producing the frequency (target Rx - 10.7) Mhz from Rx Inj J3, plus-or-minus

3 MHz.  In our case, that amounted adding approx. 2 pico-farads.  Keep

leads short, and use a temperature-0-stable capacitor.  If you have a

capacitance bridge available, use it to measure the capacitor before

installing it (capacitor tolerances at this low range can be 30% or more).

Be extremely careful! Even extremely tiny pieces of solder loose inside

the VCO cavity can make it flakey, or cause the PLL to not lock up.

When you're within a few MHz of the target frequency, replace the side

cover and adjust C6 to produce the target frequency (Rx-10.7 Mhz).

The VCO may not be perfectly spectrally pure, so be sure that you

have identified the correct peak.  It is helpful to use a

spectrum analyser if you have one available to be sure that you have

adjusted the capacitance for the correct peak out of the VCO.  Using

the wrong peak can cause no PLL lock or flakey PLL operation.



Intermittent (or no) VCO lock may also be caused by dirty connections on

VCO control voltage line from P107 to the VCO interconnect board.  Another

suspect location is the VCO feedback RCA connector on the FGU.



2) Model D:

Frequency reference change:Precision 18 Mhz reference.  Remove reference.

Carefully take it apart.  Remove the 18 Mhz xtal and put in 20 Mhz in it's

place.  STABILITY IS MORE IMPORTANT THAN ACCURACY.  Get the best you can.

Reinstall and adjust to mid-range.



Model A:NO CHANGE! Do NOT change to 20 Mhz!



3) Model D:

PLL Frequency reference change. 18 Mhz to 20 Mhz.  Reference logic board

part numbers TRN4522A, 23A, 24A and 25A (newer version Ref Logic board):

To get 8.333 Khz reference from 20 Mhz, change the U4 divide by 9 to divide

by 10.  Cut the trace between U9 pins 1 and 2, and the trace between pins 2

and 12.  Jumper pin 1 to pin 12, and jumper pin 2 to pin 9.



Model A:

For reference logic board part number TRN8788A (Model A):Do NOT mod divisor.

Remove power (or the whole chip) from U1 and U2.   Install any missing

jumpers of JU1-4 and any missing pull-up resistors r9-r12 (10K).

Add a 4-position dip switch to the board.   A convenient place is on top

of the u12 position.  Tie all pins on one side of the switch to ground,

then jmp switch 1 to JU-1 through switch 4 to JU-4.  This provides a

16 channel range.  Jmp connector pin 22 to 23 (provides +5 to on-board chips).



4) Model D:

Channel 0 select:Channel 0  = lowest VCO frequency.  In this case, our

lowest frequency is 431.3, but we'll do 431.2 for a little breathing room.

As adapted from the manual, we use the formula for the jumpers:



(((431.2M / 3) - 140M)/8.3333K)+31-1 = 1DE Hex = 111010110 binary.

    FEDC2B.1A are the jumpers

we want, where 1 means jumper in and 0 means jumper out.



Wire the remaining switch 6 to jumper C.  Select any switch setting, and

adjust the 20 Mhz reference osc. to set the nearest 25 Khz.  Now select your

RX frequency using the dip switches and adjust the 20 Mhz reference if needed.

(Future note:For higher frequencies, add a divide-by-1024 stage after the

divide by 512 stage.)



Model A:

Channel 0 select, RX logic board.  Follow formula in book to set jumpers JU1-8

on rows A-C.  The dip switch that you added above will allow you to select

a range of 16 "channels".  You may want to calculate the channel 0 jumpers for

200Khz lower than your target frequency.  This will allow you dip switch

selection of several channels above and below your target frequency.  When

you are finished, set the dip switches to select your channel.



5) Model D:

VCO output frequency select, reference logic board.  Remove the socket at U9.

Cut all traces to/from.  Make sure that jumper JUS is open.  Install a 5-pos

dip switch at U9, connecting pull-ups to one side, ground to the other.  Then

Connect Data A-E to switch 1-5 (pullup side). U10 is a great place to find them

all, and it is next to U9.  Jumper C can be connected across a 6th switch,

with a pull-up added.



All models

Re-hook the FGU to the radio, without re-installing it. Check for PLL

lock.  When PLL locks, adjust VCO Control voltage for about 4 volts.

The voltage is not critical - stable PLL lock is.  Check correct

channel and frequency.



All models:

Frequency adjust.  Power the radio but not the finals.  Attach a frequency

counter to the FGU port labeled RxInj (3).  Adjust reference oscillator for

Rx-10.7 Mhz.  Attach a frequency counter to TxInj (1) adjust side step

freq adj. to Tx frequency.





6) All models:

Sidestep filter retuning.   Ground J101-3 (supervisory board) on the

interconnect board (This keys the transmitter).  Monitor the result

from Tx Inj J1.  You are looking for your desired transmit frequency.

Check the transmit frequency.  Adjust the 15.7 Mhz Sidestep Oscillator

for exact transmit frequency.  Loosen the 5 locknuts on the underside of

the unit and adjust for peak and cleanest signal.  Carefully tighten

locknuts, power off, and re-install FGU.



7) All models:

Injection filter retuning.  Power the radio but not the finals.  Attach

a micro-ammeter from Rx meter-6 to Rx meter-7.  Adjust L12, L13 and L14 for

best peak.  The markings for L12-14 are found on the interconnect board near

the RX meter socket.  Note:min reading is 10 uA.  Our best peak was 28 uA.

If you have trouble getting an initial reading, hook analyzer to injection

filter out (hole in mixer circuit board).  Set analyzer to 10.7 Mz below

rx freq and tune L12-14 until a reading is seen on the mico-ammeter.



8) All models:

TX Trisolector (diplexor) retuning.  Disconnect the cable from the isolator

output.  At that cable connector, apply signal generator at the transmit

frequency (that cable is feeding the TX cavities).  Alternately, you

can put the radio into transmit (without the finals powered).  Connect

the spectrum analyser to the antenna connector, and apply radio power

(the finals should not be powered).  Loosen the lock nuts for the TX

portion of the trisolector only, and adjust the slugs for peak output.

Multiple passes will be needed.  In general, you will be turning

clockwise to get down to the ham band.  Repeat the procedure using

a handi-talki at 2+ watts as input and a wattmeter on the output.

Then repeat with a 25 watt + mobile and a wattmeter.



9) All models:

Isolator retuning.  Do all adjustments using a non-metalic tool.  Connect the

rf generator to the isolator input at the TX frequency, and connect the

analyzer to antenna connector.  Peak by adjusting C1 & C2. C1 matches the PA

output to the isolator input, and C2 matches the isolator output to the

trisolector input.  You may need to remove the isolator cover.



Connect the finals to the isolator.  Connect the wattmeter between the

isolator output and the TX cavity input.  Connect a dummy load to the

antenna connector.  Set the Power Control Adjustment at mid-range.  With

finals powered, key the transmitter (by connecting TX METER pin 9 to ground)

and adjust C2 for max forward power, and L7 (the first TX cavity of the

trisolector) to obtain the best compromise between maximum forward

power and min reflected power.



Reconnect the isolator to the trisolector.  Connect the watt meter

and dummy load to the input port of the isolator.  Connect a 20-30 watt

radio (at the TX frequency) to the antenna connector in place of the

dummy load.  Adjust C3 for minimum reflected power (power from the

isolator into the finals).



10) All models:

RX Trisolector (diplexor) retuning.  Apply the signal generator to the

antenna connector at the recieve frequency.  Remove the cover plate from

the receive mixer, and connect the spectrum analyser at the RX cavity exit.

Loosen the lock nuts for the receiver portion only, and apply power.  Tune

for peak signal.  In general, you will be turning clockwise to get down to

the ham band.  Use the minimum signal generator input needed to detect and

adjust slugs.



Remove the spectrum analyser connection and replace the RX cavity cover.

Attach a DC voltmeter from J102-5 to ground and repeat the adjustment for

peak magnitude.  Alternately, you may use the analyzer to peak the 10.7Mhz

IF on the IF board.



11) All models:

Audio Board mods (for those using the internal audio board):

Remove R79 and R80 (handset mic bias voltage no longer needed)

Remove C16 and Q5 (25 mA power reduction of unused circuitry)



12) All models:

Suggested mods for attaching external controller (do these on

the solder side of the interconnect board):





Jmp J101-3 to J101-16 (XMIT control pass-through to J110-3 PTT)

Jmp J101-7 to J101-12 (audio pass-through to J110-1)

Jmp J101-1 to J101-13 (COS pass-through to J110-4)

(Handset Mic Audio is applied to J110-2)



For those planning on using the audio path from the IF board to

the audio board, you may want to replace R126 on the interface

board with a wire.  This is a 10K series resistor in the audio

path.





13) All Models:

You will need squelch and mute circuitry.  Using op-amps, this

can be done within the radio by replacing the audio board with

an audio/squelch/mute board.  See schematic.



You can also use any available squelch and/or PL decode chips.



=============================================================================

For areas of the country which do NOT follow the ARRL UHF bandplan, and

therefore use a positive repeater offset

=============================================================================

This is what we would try if we had to, but we've never had to do it.



1) Raise the VCO to Rx+10.7 MHz by cutting away the strip capacitor in the FGU.



2) Follow all other mod procedures and hope that the transmitter side tuning

slugs, finals, etc. go another 5 MHz farther down.



Here's the theory: when two frequencies mix, the result is both the sum and

the difference.  In the original design, the receiver 10.7 Mhz IF was formed

by Rx-VCO.  This way it's VCO-Rx.  Either way, the low-pass filtering keeps

only the 10.7 IF result.  On transmit, Tx was formed by VCO+15.7 MHz.  This

way it's formed by VCO-15.7 MHz.  Either way, the sidestep filter passes only

the desired TX frequency.





Initial radio checkout...

1) Remove covers.



2) Remove the following boards and save for parts (especially bus connectors):

OPTION

SUPERVISORY LOGIC

INTERFACE

AUDIO (only if you will be some other mixer board)



3) For reference logic TRN6507, TRN8788A jmp connector pin 22 to 23

   (provides +5 to on-board chips).



4) Interconnect Board Jumper change:install JU101, JU102

   This enables XMIT keying.



5) Using a current limited supply, with current limited to about 1 amp,

   apply 13.8v DC to the RX power connection of the front connector.  This is

   pin 6.  You should see a current draw of about 500ma.



6) Using a DVM, you should measure the following voltages on the interconnect

   board: 

    TP1   13.7v        (Main supply)

collector Q104 TP3   10.2v        (reg 10.2)

    J105-23    5.1v        (reg 5.1)

    J106-19   10.2v        

    J106-4    10.2v        (Fused on Ref. Logic bd. 3/4amp fuse)

 Rx Logic TP5     4.0v        (PLL is LOCKED)