The part number for the MITREX UHF manual is 68-

The part number for the MITREX UHF manual is 68-81045E75,

UHF and VHF MITREX elements should be KXN1086 for receive and KXN1088 for transmit.

The crystal companies know the specs for the elements, all they want to know from you is the transmit and receive

frequencies.For the MICOR, but not the MITREX, there is a company called Channel Element HQ,

1-800-237-9654. They maintain a very large stock of used channel elements. They will sell you one on your

frequency for $25.00 or $20.00 with trade in. The only catch is: do they have your frequency?

Amateur frequencies are commercial some where else in the world, so they probably do.

All you need to give them is the model number of the element, the frequency and, for receivers, if its high or

low injection. The advantage of them is there is no waiting for re-crystaling. This modification of a MITREX

440 to a 9600 full-duplex repeater is from William Lyman, [email protected]

I have successfully completed assembling a 9600 fullduplex data repeater. I used a Mitrex T44 with an

MFJ 1270 TNC and Tapr 9600 baud modem with bit regen. This repeater in now in use at Bethany CT,

Portland Ct, and Bridgeport Ct and they are all working GREAT. My first feeling was it wasn't going to work.

I though that internal desens would kill the receive. Here are some hints and suggestions for making this work

Please remember these mods for a Motorola Mitrex T44 UHF model.

1) Be sure to get the elements temp comped! I didn't at first and as it got used it drifted badly as the unit got hot.

2) I made 2 of the mods that MoAmps published for increasing high frequency response at the limiter/Detector.

If you are on a fringe than this will really help.

2a) Remove C240 a .0022 cap. This can be achieved by physically grabbing it with pliers and breaking it away

from the PC board. Or you can remove the shield cover and unsolder it. I did the later and thats what I suggest.

2b) Remove C451 a 220 cap between U403a pins 2 and 3.

2c) Replace R231, 75.k resister with 2.2k resister

3) Receive audio is (Det) is available on pin 11 of the control cable connector.

4) Lock receive element on. Please note this is for fullduplex only this will cause unit receiver circuitry to be

on all the time. If you did this mod in simplex the modem would false by hearing you only transmitted signal

and would take longer time to lock.

4a) Locate Q1 and add a jumper across the e and c junction

5) The following are for transmitter mods

5a) locate pin 15 of the interconnect board. This is not pin 15 where the control cable connects but pin 15 on

the connector that connects the interconnect PCB to the main PCB. Solder wire from this connection to pin 1

on the backside of where the control cable connects. With unit facing you (lock towards you) this will be the top

right most pin. You will see either a white jumper or a coil (small) that goes from pin 1 to the rest of the circuitry.

Remove one side of this jumper.

5b) Remove one side of each of the following caps. C507,C508,C509. This will remove the splatter filter

allowing you to use Q503 and q504 to drive the element. You could drive the element directly but I found

that there was distortion when driving the element hard. This also matches the Impedance on the Element.

6) Xmit audio is now available on pin 1 on the control cable connector.

7) Rec/Xmit ant connections

7a) On my unit the xmit connection to the ANT relay was hard wired on to the final AMP.

I didn't have any small coax so I left the ANT relay in. My transmitter connection is at the existing ANT connector.

For the receive I unplugged (RCA JACK). Trace back from ANT switch. I taped the jack and left in place.

I drilled a hole in the top cover over where the RCA jack plugged in. I then made a cable with an RCA jack thus

making this the Receiver connection. I only drilled the hole in the cover because covers are easy to come by if I

make a mistake.

8) Cable connections

8a) The following connection to the motorola female connector should be made. pin 17 to pin 6 this is negative

pin 4 to pin 12 to + fused at 2 amps (Rec/Xmit enable) pin 19 + fused at 20 Amp pin 13 PTT, pin 1 xmit audio

pin 11 rec audio

9) Summary

9a) it is very important that the receive cable be of the best quality. Remember it is VERY close to the Xmiter.

When you adjust the Xmiter follow the manual very close. You can't have any spurs.

9b) I did experience some desense from the xmiter circuitry in the range of .03 uV. I find that to be almost non

existent. There might be other ways or mods. These have worked for me in 3 installations. The mods are made

so if you decide to resale the radio. Just replace cover, install splatter caps, Install jumper on pin 1, And remove

jumper from pin 15 interconnect to pin 1 on cable connector. And resale. I am running the unit at 50 watts.

It get warm, well very warm. I would suggest that you place some blower fans blowing on the heat sink.

You could get a T74 (110 watt) unit and run it all day at 50 watts, But they are very hard to come by.

73's and good luck

This modification of a MICOR UHF to duplex mobile is from Jim Reese, [email protected]

Why would you want a duplex mobile, you ask? Once you've experienced it, you'll never go back to jap-trac's.

This describes how to take a standard UHF micor mobile radio and make it work as a full-duplex mobile radio.

Since Texas is high-in, low-out on UHF, this also includes which cap changes are required to make the radio

receive below 445 MHz. There are diagrams referenced in this text. If you are unable to figure out what to do

without the diagrams, mail me at [email protected] and I'll try to get you a copy of the diagrams.

Jim Reese WD5IYT

Conversion of Motorola MICOR UHF Radio For Use as a Duplex Mobile

This conversion is not for the faint-hearted. Make sure you are very familiar with the operation of the Micor radio

before attempting this conversion. As with all modifications of this type, insure that the radio is operating correctly

BEFORE any modifications are made. It is much easier to fix it before you hack it up. Do not attempt this conversion

without a service manual. You need the PC layouts and tune up instructions from the service manual in order to

perform the modification. Useful Motorola Part Numbers 68-81015E70-H Manual for UHF MICOR

KXN-1024 5ppm Channel Element for UHF MICOR , KXN-1029 2ppm Channel Element for UHF MICOR

KLN-6210A PL Encode Reed TLN-8381A PL Decode Reed 66-84690C01 Contact Removal Tool for MICOR

plugs TKN-6458A Large Fuse Holder for Primary Power (40A)

Crystal Ordering Information;When ordering crystals, specify the KXN-1024A channel element number.

Always order the crystal on the RECEIVE frequency. If your radio will be a high transmit unit, the crystal will

be LOW side injection. For low transmit radios, order the crystals on HIGH side injection. This will flip the

transmit offset to the other direction.

Conversion Instructions

Step 1: Make sure that the radio is operating properly by tuning it up with one of your crystals before any

modifications are made. If you are using the radio as a high transmit unit, you must make the capacitor

changes in step 2 for the radio to work properly.

Step 2: If your radio will be receiving below 445 MHz, change C117 to 27pF, C119 to 39pF, and C125 to

12pF on the receiver board. This is not necessary if the radio will be receiving above 445 MHz.

Step 3: You must make some modifications to the control board and the receiver audio/squelch board in order to

make the radio full duplex. First, remove JU-905 on the control board. Next, jump pins 1 and 4 of the audio

squelch board. On the later version audio squelch board, there is a place for a jumper (JU-202), on earlier units,

just make the jump with wire wrap wire. Add capacitors at the following points on the audio squelch board.

Add a 100pF cap between P903-5 and P903-6. On IC-201, add 15pF caps between pins 3 and 4, and between

pins 3 and 5. Add 100pF caps between pins 6, 7, 11, and 13 of IC-201 and ground. On IC-202, add 15pF

caps between 5 and 9, 5 and 13, and a 33pF cap between 5 and 15. This makes the board less susceptible to RF.

Keep the leads on these caps as short as possible.

Step 4: Carefully remove the front casting from the chassis. This is done by removing the four screws top and

bottom as well as two screws on the control head plug. This is kind of tricky, so be careful to remember how you

got it apart so you can re-assemble it later. Examine the Power Amplifier section of the radio and notice the miniature

connector which connects the output of the PA to the circulator. Unplug this connector from the circulator using a

needle nose plier or hemostat. Turn over the radio and remove the power control board. This will expose the top

plate of the circulator. Remove the circulator by carefully removing the sensing wires which connect to the power

control board and the two screws which hold the circulator in. You will have to unplug the receive antenna coax from

the preselector unit in order to remove the circulator. Set the circulator aside for later modification.

Step 5: Mount a BNC chassis mount connector on the top side of the front casting on the side opposite from where

the lock is located. This will be the receive antenna connection. Be very careful to locate this connector so that it does

not hinder the operation of the latch mechanism. Attach a small coax to this connector and route it to the receive antenna

jack on the preselector unit. Drill a hole in the front of the radio chassis to pass the coax. This will be obvious once you

have examined the unit with the front casting removed.

Step 6: This is the toughest part of the conversion, the circulator modification. Remove the cover from the circulator

unit. You will notice that there is a circulator, an output filter, the antenna switch, and the circulator reject load. There

are three trimmer caps, only one of which has an access hole in the top plate. Measure and drill the top cover so that you

have access to all three trimmers from the outside. This is necessary because the cover affects the tuning of the circulator.

After drilling the cover, set it aside. You must now remove the antenna relay. This is a small relay on the right side of the

circulator. The small dark red or green rectangular unit with a wire coming from the relay is the reject load for the circulator.

This is a ceramic 75W 50 Ohm resistor. The relay switches the output port of the circulator between the receiver and the

reject load. Be EXTREMELY CAREFUL when soldering on the reject load, as the top terminal can break off of the

ceramic very easily. I suggest cutting the wire from the relay, removing the relay, and then removing the wire from the

load resistor. Once the relay is removed, wire the dummy load back to the output port of the circulator which is on the

common side of the relay. Refer to the manual for the circuit. The easiest way to accomplish this is with a small piece

of teflon coax (RG-188). Run from the circulator port to the reject load. You can solder to the circulator case for the

shield on the load end of the coax. Replace the cover on the circulator and reinstall it in the radio.

Tuning Instructions

Before tuning, disable the receiver AFC by soldering a wire from the "AFC OFF" trace on the receiver board to

ground. The procedure for disabling the AFC is described in the receiver tuning instructions section of the service

manual. Tune the radio per the Motorola manual. Once you have achieved this, you need to tune the circulator.

The following procedure should be followed: Remove the power control board, and power the radio with a supply

having a current meter. Attach a jumper or clip lead from feedthrough C527 on the Controlled Stage in the PA

compartment and feedthrough C536 on the driver stage in the PA compartment. This will force the radio to

maximum power output. Key the transmitter and tune the three circulator capacitors for maximum power output.

Reinstall the power control board, and preset the drive limit pot fully counter-clockwise. Set the power set pot

to the desired power output level. Key the transmitter and tune the center circulator capacitor (the only one

accessible from the top of the power control board) for minimum current draw. You should be able to make

several Amps difference without affecting the power output. Turn the drive limit pot 1/4 turn clockwise, or until

power just starts to fall off.

That's it. Remember to always set the receive frequency first when setting frequency, as this affects the transmitter

also. Set the transmitter with the offset trimmer coil on the exciter board. Make sure that you have adequate cooling

space around the PA heat sink fins when the radio is installed. The Micor PA is not easy to fix, and when it blows,

it blows big.

This modification of a MICOR UHF to repeater service is from Jim Reese, [email protected]

Instructions for Conversion of Motorola UHF Micor to Repeater Service

This modification is not for the faint-hearted. Be sure you are very comfortable with the operation of the MICOR

radio before you attempt this modification. A thorough understanding of the way the MICOR radio and control system

works is absolutely essential for the success of this conversion.

Modification Notes Whenever "Molex Pin x" is mentioned, it refers to the Armadillo Standard connector.

This is a small, 9 pin Molex connector which serves as the interface for all of the Armadillo radios.

Use a Female connector on the radio end. The standard pinout of the connector is: 1 - Ground

2 - Receive Audio Output 3 - n/c 4 - Transmit Audio Input 5 - COS Output 6 - PTT Input 7 - n/c

8 - PL Decoder Output (Sense) 9 - PL Select Input

The COS output and PTT input are open-collector to ground signals. Pin 8 goes to +9.6 V when PL is decoded.

Pin 9 is ground for PL, open for Carrier. These modifications allow "PL and Squelch" operation. This means that

when in PL, the normal squelch circuit still operates. This avoids long noise bursts upon unkeying. If using an

Advanced Computer Controls controller, the signal at pin 8 is run to the "PL Sense input" on the controller.

It will drive this input directly. Order the crystal on the repeater RECEIVE frequency. You must specify HIGH SIDE

INJECTION. If you do not order a high side crystal, the transmit offset will be 5 MHz above the receive frequency,

instead of 5 MHz below. I recommend sending the channel element to the crystal manufacturer for temperature

compensation. Use a KXN-1024 element for 5ppm accuracy, or use a KXN-1029 element for 2ppm accuracy.

Disable the receiver AFC by jumping the appropriate pin of the channel element to ground.

List of Tables and Illustrations There are several illustrations which are detailed below. Refer to them as needed when

modifying or constructing pieces of this project.

Table 1: This is a complete hookup chart for the control head plug and interface board.

Figure 1: Schematic of control head plug, with simple diagram.

Figure 2: Board Layout of audio squelch board detailing added capacitors.

Figure 3: Detail of circulator unit showing location of major components.

Figure 4: Schematic of circulator unit before modification.

Figure 5: Schematic of circulator unit after modification.

Figure 6: Schematic of interface board.

Figure 7: Rough layout of interface board.

Useful Motorola Part Numbers

68-81015E70-H Manual for UHF MICOR

KXN-1024 5ppm Channel Element for UHF MICOR

KXN-1029 2ppm Channel Element for UHF MICOR

KLN-6210A PL Encode Reed

TLN-8381A PL Decode Reed

01-84307A89 Empty Control Head Plug less cable, complete with pins

66-84690C01 Contact Removal Tool for MICOR plugs

TKN-6458A Large Fuse Holder for Primary Power (40A)

Step-By-Step Instructions for Modification

Step 1: Make sure that the radio operates properly BEFORE any modifications are done. If there are problems

with the radio, they will be easier to fix before the mods are done.

Step 2: If you are satisfied with the operation of the radio, construct the control head plug per figure 1 and table 1.

Use miniature pots and switches inside the control head plug. It is rather tight inside, so be careful to check that the

connector will re-assemble before you drill it up. After you have constructed the connector, make the following

connections inside the radio:

Jump control head pins 3, 8, and 22 to "A+" on the control board. Jump pins 9, 11, and 17 to ground on the control

board. Next locate the two feedthrough caps which power the Transmitter Power Amplifier. They are just to the left

of the control head plug on the bottom side of the radio. One will have a red wire, and the other a black wire.

Jump from the feedthrough with the red wire to the "A+" trace on the control board. Jump from the feedthrough

with the black wire to the ground trace on the control board. There is a reverse polarity protection diode on the

control board which can be used to make these connections. Next, plug your control head plug into the radio and

verify proper operation with the new control arrangement. If there are problems here, troubleshoot them NOW.

Do not wait until later, as you may be chasing more than one problem.

Step 3: You must make some modifications to the control board and the receiver audio/squelch board in order to

make the radio full duplex and to make preparations for the interface board. First, remove JU-905 on the control

board. Then, jump the F1 channel element to ground as described in the Motorola manual. Next, jump pins 1 and 4

of the audio squelch board. On the later version audio squelch board, there is a place for a jumper (JU-202),

on earlier units, just make the jump with wire wrap wire. Next, remove a jumper on the audio squelch board which

goes from pin 3 of the PL decoder to IC-202 pin 8. This is near the pins which the PL board plugs into. Next, ring

from pin 3 of the PL decoder to pin 11 of the audio squelch board with an ohmmeter. There should be continuity here.

If not, add a jumper. The later boards have a trace from pin 3 of PL to pin 11 of audio squelch, on earlier boards, pin

11 is unused, and you should jump from PL decoder 3 to audio squelch 11 with some wire wrap wire. Add 15pF

capacitors between the following pins on the two chips on the audio squelch board. Figure 2 details the location of

these caps. On IC-201, add a cap between pin 3 and 4, and between pin 3 and 5. On IC-202, add caps between

5 and 9, 5 and 13, and two caps between 5 and 15.This makes the board less susceptible to RF.

Step 4: Next, carefully remove the front casting from the chassis. This is done by removing the four screws top

and bottom as well as two screws on the control head plug. This is kind of tricky, so be careful to remember how

you got it apart so you can re-assemble it later. Next, examine the Power Amplifier section of the radio and notice

the miniature connector which connects the output of the PA to the circulator. Unplug this connector from the circulator

using a needle nose plier or hemostat. Next, turn over the radio and remove the power control board. This will expose

the top plate of the circulator. Remove the circulator by carefully removing the sensing wires which connect to the

power control board and the two screws which hold the circulator in. You will have to unplug the receive antenna

coax from the preselector unit in order to remove the circulator. Set the circulator aside for later modification.

Step 5: Procure a BNC chassis mount connector for a receive antenna jack.Mount this connector on the top side of

the front casting on the side opposite from where the lock is located. Be very careful to locate this connector so that it

does not hinder the operation of the latch mechanism. Attach a small coax to this connector and route it to the receive

antenna jack on the preselector unit. Drill a hole in the front of the radio chassis to pass the coax. This will be obvious

once you have examined the unit with the front casting removed.

Step 6: This is the toughest part of the conversion, the circulator modification. Figures 3, 4, and 5 detail the

conversions. Remove the cover from the circulator unit. You will notice that there is a circulator, an output filter, the

antenna switch, and the circulator reject load. There are three trimmer caps, only one of which has an access hole in

the top plate. Measure and drill the top cover so that you have access to all three trimmers from the outside.

This is necessary because the cover affects the tuning of the circulator. After drilling the cover, set it aside.

You must now remove the antenna relay. This is a small relay on the right side of the circulator.The small dark red

rectangular unit with a wire coming from the relay is the reject load for the circulator. The relay switches the output

port of the circulator between the receiver and the reject load. You must remove the relay and wire the dummy load

back to the output port of the circulator which is on the common side of the relay. Refer to the diagram for the circuit.

The easiest way to accomplish this is with a small piece of teflon coax (RG-188). Run from the circulator port to the

reject load. You can solder to the circulator case for the shield on the load end of the coax. Replace the cover on the

circulator and reinstall it in the radio.

Step 7: Construct the interface board using the schematic and board layout in the packet. Install this board on the three

unused mounting tabs near the rear center of the radio. These tabs are above the control board. Wire the board up as

described in table 1. At this point, the radio will be operating full duplex, and you should be able to put the radio in PL

by flipping the switch on the control head plug to the PL position. Verify that you have +9.6 volts at the 9 pin molex

connector PL SENSE pin when the correct PL code is being sent. Also verify correct receive audio gating and

COS action.

Tune Up Instructions

Tune the radio per the Motorola manual. Once you have achieved this, you need to tune the circulator. The following

procedure should be followed:

Step 1: Remove the power control board, and power the radio with a supply having a current meter.

Step 2: Attach a jumper or clip lead from feedthrough C527 on the Controlled Stage in the PA compartment and

feedthrough C536 on the driver stage in the PA compartment. This will force the radio to maximum power output.

Step 3: Key the transmitter and tune the three circulator capacitors for maximum power output.

Step 4: Reinstall the power control board, and preset the drive limit pot fully counter-clockwise.

Set the power set pot to the desired power output level. I recommend no more than 50W out for a 75W radio,

and no more than 60W out for a 100W radio. The 25 and 45W radios are rated continuous duty at 25W output.

Step 5: Key the transmitter and tune the center circulator capacitor (the only one accessible from the top of the power

control board) for minimum current draw. You should be able to make several Amps difference without affecting the

power output.

Step 6: Turn the drive limit pot 1/4 turn clockwise.

That's it. you are now ready for major repeating action. Remember to always set the receive frequency first when

setting frequency, as this affects the transmitter also. Set the transmitter with the offset trimmer coil on the exciter board.

Make sure that you have adequate forced air cooling on the PA at all times during operation.

The Micor PA is not easy to fix, and when it blows, it blows big.

This modification of a MICOR VHF to repeater service is from Jim Reese, [email protected]:

Instructions for Conversion of Motorola VHF Micor to Repeater Service

This modification is not for the faint-hearted. Be sure you are very comfortable with the operation of the MICOR radio

before you attempt this modification. A thorough understanding of the way the MICOR radio and control system works

is absolutely essential for the success of this conversion.

Modification Notes

This modification was developed for radios having receiver RF/IF board series

TLD8270A; audio/squelch models TLN4310A-2 thru TLN4310A-5; and exciter models TLD8261A, TLD8262A,

TLD8261B, or TLD8262B.

If your radio differs from these part numbers, all or part of this modification may be different from the descriptions.

Use your judgement to alter these instructions as necessary. Whenever "Molex Pin x" is mentioned, it refers to the

Armadillo Standard connector. This is a small, 9 pin Molex connector which serves as the interface for all of the

Armadillo radios. Use a Female connector on the radio end. The standard pinout of the connector is:

1 - Ground ,2 - Receive Audio Output, 3 - n/c, 4 - Transmit Audio Input, 5 - COS Output, 6 - PTT Input, 7 - n/c

8 - PL Decoder Output (Sense), 9 - PL Select Input

The COS output and PTT input are open-collector to ground signals. Pin 8 goes to +9.6 V when PL is decoded.

Pin 9 is ground for PL, open for Carrier.

These modifications allow "PL and Squelch" operation. This means that when in PL, the normal squelch circuit still

operates. This avoids long noise bursts upon unkeying. If using an Advanced Computer Controls, S-Com or other

commercial controller which requires an active high PL sense signal, the signal at pin 8 can be attached to the "PL Sense

input" on the controller . It will drive this input directly. On the S-Com controller, the pull up resistor on the PL sense

input must be removed for proper operation.

List of Tables and Illustrations

There are several illustrations which are detailed below. Refer to them as needed when modifying or constructing

pieces of this project.

Table 1: This is a complete hookup chart for the control head plug and interface board.

Figure 1: Schematic of control head plug, with simple diagram.

Figure 2: Board Layout of audio squelch board detailing added capacitors.

Figure 3: Schematic of interface board.

Figure 4: Rough layout of interface board.

Useful Motorola Part Numbers \

68-81008E40-D Manual for VHF MICOR

K1007A TX Channel Element for VHF MICOR

K1005A RX Channel Element for VHF MICOR