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- 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-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)
-
-
-