Motorola Micor By Bruce Perens KD6OTD
Any errors that have crept in are my fault, not theirs. However,
nobody but you is responsible if you follow these instructions
and something goes wrong. If you have more information on these
radios, please send it to me.
Thanks
Bruce Perens KD6OTD/AE
Motorola's parts hot line is 1-800-422-4210. The people at this
hot line
wanted $11.55 for the MITREX manual and took my credit-card
order right away.
My local Motorola parts depot quoted $25 for the same manual, did
not have it in stock, and then could not figure out what the shipping
cost would be so they suggested I drive out to the depot and pick it
up when they got it. >From this experience I would suggest that you
use the 800 number for parts.
The part number for the MITREX UHF manual is 68-81045E75,
$11.55
As for channel elements, you can either send them in to one of the
many companies that do them, or you can buy crystals directly and
solder
them in yourself. Companies that will make crystals are:
JAN Crystals, 1-800-526-9825, $11.00 per crystal.
Bomar, 1-800-526-3935, $15.00 per crystal or $25 to re-crystal
your channel element for you.
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, lyman@a3bee2.radnet.com:
I have successfully completed a 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 hits 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 maked 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 that 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