KENWOOD TM-621/721 & TM-631/731

                                      CROSS BAND REPEATER MODIFICATION 


THIS IS A VERY SIMPLE MODIFICATION TO RELEASE THE CAPABILITIES OF THESE FINE
DUAL-BAND RIGS TO ALLOW FOR CROSS-BAND REPEAT OPERATION. HERE ARE MANY 
POSSIBILITIES WITH THIS FEATURE. NE EXAMPLE IS MY SITUATION. I WORK ABOUT 20 
MILES FROM HOME AND OUR LOCAL 2 METER REPEATER. I SET MY MODIFIED TM-731 UP 
WITH THE 2 METER SIDE ON OUR REPEATER FREQUENCY AND THE 440 SIDE ON A SIMPLEX 
FREQUENCY. THIS GIVES ME ACCESS TO THE REPEATER FROM MY OFFICE. AS FAR AS I 
CAN DETERMINE THIS OPERATION IS PERFECTLY LEGAL... IF YOU: 

1) ARE IN A CONTROL POSITION (CAN SHUT DOWN THE FUNCTION, IN THE EVEN OF 
TROUBLE) AND 2) IDENTIFY YOUR CROSS-BAND REPEATER, IN ACCORDANCE WITH 
THE REGULATIONS.

HERE IS THE PROCEDURE:

1) DISCONNECT THE POWER, AND BOTH ANTENNAS FROM THE RIG.

2) REMOVE THE TOP AND BOTTOM COVERS TO THE RIG. WHEN OPENING THE TOP PANEL BE 
CAREFUL TO NOTE THE POSITION OF THE SPEAKER CONNECTION PLUG. REMOVE THE 
SPEAKER WIRE PLUG.

3) REMOVE THE SIX SILVER SCREWS THAT ARE HOLDING THE FRONT PANEL TO THE 
CHASSIS. CAREFULLY SLIP THE FRONT PANEL AWAY FROM THE CHASSIS.

4) LOOKING DOWN INTO THE BACK OF THE FRONT PANEL LOCATE THE LITHIUM BATTERY.
IT IS SILVER AND SLIGHTLY LARGER THAN A QUARTER. ORIENT THE FRONT PANEL 
SO THAT THE TOP CONTACT TO THE LITHIUM BATTERY IS COMING DOWN FROM ABOUT
THE 11 O'CLOCK POSITION TOWARDS THE CENTER OF THE BATTERY.

5) OW LOCATE THE CIRCUIT BOARD TRACE THAT EXITS FROM ABOUT THE 9 O'CLOCK 
POSITION FROM UNDER THE LITHIUM BATTERY AND THEN TURN DOWN TOWARDS THE 
CLOSEST EDGE OF THE CIRCUIT BOARD. HAT TRACE ENDS JUST BEFORE IT REACHES
THE CIRCUIT PART R121 (NOT IDENTIFIED ON THE BOARD). IT IS A VERY TINY
ALL GREEN "RESISTOR" (VALUE 0 OHMS). THIS IS THE CROSS-BAND REPEATER MOD.
TO CONFIRM THAT YOU HAVE THE CORRECT PART, THERE SHOULD BE A COPPER
COLORED CONTACT AREA JUST TO IT'S RIGHT.

6) USING VERY SMALL SNIPS OR SMALL NEEDLE-NOSE PLIERS, COMPLETELY REMOVE THIS
SHORTING DEVICE. BLOW OUT THE CIRCUIT BOARD TO REMOVE ANY FOREIGN DEBRIS.
THAT IS ALL THEIR IS TO IT... YOU'RE DONE. CLOSE UP THE CASE.


OPERATING INSTRUCTIONS

1) SET YOUR OPERATING FREQUENCIES ON BOTH THE MAIN AND THE SUB-BANDS. THIS 
INCLUDES THE OFFSET'S) AND PL TONES, IF ANY. OUR CAN'T USE CTCSS.

2) DEPRESS THE YELLOW FUNCTION KEY. THEN PRESS (WITHIN 5 SECONDS) THE A.B.C.
KEY. YOU SHOULD NOTE THE ADDITION OF FOUR MORE DECIMALS IN THE FREQUENCY
READOUTS, TWO IN EACH. THIS INDICATES THAT THE CROSS-BAND MODE IS
ACTIVATED.

3) TO TURN OFF THIS MODE REPEAT THE STEPS IN NUMBER TWO (ABOVE).


NOTES:
------

HERE ARE A FEW OPERATIONAL NOTES FROM MY EXPERIENCE. WHEN IN THE CROSS-BAND 
MODE ALL FRONT PANEL BUTTONS ARE TEMPORARILY DEACTIVATED. THE MICROPHONE WILL
PICK UP LOCAL AUDIO WHEN THE TRANSMITTER IS ON, DISCONNECT OR RELOCATE IT TO 
GET RIDE OF FEEDBACK WITH YOUR HAND-TALKIE. OUR MUST WAIT FOR THE CARRIER OF 
THE REPEATER OR STATION TO COMPLETELY DROP OUT BEFORE YOU TRANSMIT. THIS 
CHARACTERISTIC MAKES AUTO PATCHING IMPOSSIBLE. THERE IS A 3 MINUTE TIME-OUT 
TIMER BUILT INTO THE CIRCUIT TO PROTECT YOUR RIG AND YOUR CAR BATTERY.

GOOD LUCK!
     

All the mods are captured by Packet. 
KB2LJJ    Radio Mods Database 
take now responsibility or liability for any 
damage resulting from this modification.