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MaraTracs and M400s can
be used for repeater receivers and transmitters.
Just like their smaller cousins (MaxTracs,
Radiuses, and GM300s), you need two radios, since
none of these can operate full duplex. These also
suffer from most of the same woes as MaxTracs: the
transmitter will need a lot of cooling air and it
should be run at no more than 50% of its rated
power. The transmitter will probably shut down
when the microprocessor thinks it's getting hot,
so a manual power control might be necessary.
(Perform the same modification to the logic board
as for a MaxTrac; see that article on
Repeater-Builder.) These radios also have an
antenna relay that should be bypassed to eliminate
a source of future trouble.
The biggest
problem is that there are no spare pins on the
control cable connector on the front of the
radio, nor is there an external accessory jack
to get additional signals in to, or out of, the
radio. This is really only an issue for the
receiver. If you're willing to run the radio
with its cover off, or drill/cut an opening
either in the top cover or somewhere in the
casting, you can bring wires in and out of the
radio. You should consider using feed-through
capacitors for the signals, just to reduce the
chance of signal leakage.
I prescribe to
the "KISS" principle: "Keep It Simple, Stupid."
The less modifications I have to make to a
radio, the better. This also makes it quicker
and easier to configure replacements, when
necessary.
There are
several articles about repeater interfacing
using MaxTrac radios on this web site. This
article will follow the simple scheme detailed
there. The following signals are minimally
required for any repeater setup:
- Power to both radios
- Ground to both radios
- Transmit Audio from the controller to the
transmitter
- Push-To-Talk from the controller to the
transmitter
- Receive Audio from the receiver to the
controller
- Carrier (and PL/DPL) Detect from the
receiver to the controller
There are usually
multiple places each of these signals can be
accessed; they will be detailed below, but first,
let's see what's available at the various
connectors throughout the radio.
NOTE:
Most of the signals and
observations described below are based on the
configuration of my MaraTrac radios: low-band with
advanced control heads (A7) and remote squelch. If
you configure the radio for a different head type,
some signals will be different.
Control
Head Connector (J1) on front of radio:
This connector normally
feeds a control head. It is the only connection
point accessible with the radio's covers
installed. The pins and signals are described in
the table below. Pin 1 is in the lower right
corner when looking into the front of the radio
with the connector at the right. The lower row has
pins 1-8 (right to left), the upper row has pins
9-16 (right to left), and the large pins in the
middle are 17-19 (right to left) with the jack
screw between pins 17 and 18. All of these numbers
are embossed in the plastic connector body and the
photo has most of them identified.
Pin |
Signal Name or Use |
Notes |
1 |
Serial
Clock |
|
2 |
Analog
Ground |
|
3 |
Speaker
High |
Do Not
Ground! |
4 |
B+ from
Control Head |
Green
Ignition Control wire |
5 |
Speaker
Low |
Do Not
Ground! |
6 |
Data Out |
|
7 |
Display
Enable |
|
8 |
Data In |
|
9 |
Busy Light |
or Remote
Squelch |
10 |
Switched
5V |
|
11 |
Volume Top |
|
12 |
Push-To-Talk |
Ground to
Transmit |
13 |
Power
On/Off |
Ground for
ON |
14 |
Microphone
High |
Has +9VDC
on it |
15 |
Volume
Wiper |
|
16 |
Xmit Light |
See
comments below |
17 |
GROUND
(Black wire) |
Large pin |
18 |
Emergency
/ Hook |
Large pin |
19 |
A+ (Red
wire) |
Large pin |
The Busy
signal on pin 9 drives the Busy LED on the clamshell
and handheld control heads, which follows the
carrier only. On radios with Remote Squelch (only
low-band MaraTrac radios have this feature), this
line is used for the squelch pot signal. On the
advanced control heads, the Busy and Xmit LEDs are
driven by the serial clock and data lines that
handle the channel display. In fact, most of the
switches and LEDs run through the serial chips. The
older non-synthesized radios that use the same
connector (Motrac, Motran, etc.) rely on discrete
lines for every signal; nothing is shared or
multiplexed.
The Xmit Light signal on pin
16 is shared between the Light relay driver
(Horn/Light option available at the VIP connector on
the back of the advanced head) and the actual Xmit
Light signal (a 5V TTL signal that eventually lights
the transmit lamp in the clamshell head). In fact,
some other signals change function depending on the
type of control head the radio expects at the end of
the cable.
If you remove the top cover of
the radio, you now have access to a whole bunch of
connectors and signal points, but you'll probably
have to leave it off to use the radio in repeater
service.
Programming
Jack (J20) inside radio:
This is an RJ45
receptacle with signals similar to what you'd find
on a MaxTrac, Radius, GM300, or GTX radio. They
are described below. Pin 8 is closest to the main
radio connector J1.
Pin |
Signal Name or Use |
Notes |
1 |
Switched
B+ |
|
2 |
Spare |
Available |
3 |
Emergency
/ Hook |
|
4 |
Ground |
|
5 |
Microphone
Audio In |
Has +9VDC
on it |
6 |
Push-To-Talk |
Ground to
Transmit |
7 |
SCI+ |
Programming
line |
8 |
Handset
Audio Out |
Fixed
level |
Option
Board Connector (J22) inside radio:
This two-row connector
is available for options and interfacing. For some
reason, Motorola numbered the pins around the
outside, rather than the traditional odd/even
scheme used by most two-row connectors of this
type. Pin 1 is located at the far left side of the
radio, closest to the front panel. The pins are
then numbered counter-clockwise, with pin 3 being
a keyway. The table below describes the signals
available here.
Pin |
Signal Name or Use |
Notes |
1 |
Digital
Ground |
|
2 |
Switched
B+ |
|
3 |
Keyway |
Hole is
plugged |
4 |
Volume
Control top |
Jumpered
to pin 5 |
5 |
Decoded
Audio Out |
Jumpered
to pin 4 |
6 |
Microphone
High Out |
Jumpered
to pin 18 |
7 |
Analog
Ground |
|
8 |
9.6VDC |
|
9 |
Switched
5VDC |
|
10 |
Continuous
B+ |
|
11 |
SCI+ |
Programming
line |
12 |
Option-to-Audio
Spare |
|
13 |
Reference
Modulation |
From RF
Board |
14 |
VCO Lock |
Locked =
Low |
15 |
Detected
Audio In |
|
16 |
VCO
Modulation |
From RF
Board |
17 |
Push-To-Talk |
Ground to
Transmit |
18 |
Microphone
High In |
Jumpered
to pin 6 |
Audio
Board Connector (J21) underneath radio:
The photo
above shows the underside of the Audio/Squelch
board, underneath the antenna relay. Even though the
connector is occupied by pins from the Audio/Squelch
board, there are still some signals that can be
obtained from it. You will have to attach wires
directly to the audio board or to the back of J21
(on the front panel board) to access them. They're
described in the table below. Like J22 above,
they're numbered in a unique fashion, with pin 1
towards the outside and rear of the radio, going
counter-clockwise when viewed from the bottom of the
radio.
If you remove the
Audio/Squelch board, you get a better view of the
connector. As this radio has remote squelch
capability, the keyway (plugged hole) normally
present at pin 12, actually has a contact and is
used for the remote squelch signal.
Pin |
Signal Name or Use |
Notes |
1 |
Ground |
|
2 |
Switched
B+ |
|
3 |
Speaker
Low |
Do Not
Ground! |
4 |
Speaker
High |
Do Not
Ground! |
5 |
Analog
Ground |
|
6 |
Audio PA
Mute |
|
7 |
9.6VDC |
|
8 |
Detected
Audio |
|
9 |
VCO Lock |
Locked =
Low |
10 |
Channel
Activity |
|
11 |
Squelch
Decision |
Active Low |
12 |
Keyway /
Remote Squelch |
|
13 |
Audio-to-Option
Spare |
|
14 |
Audio
Input |
|
15 |
Speaker
High |
Do Not
Ground! |
16 |
Speaker
Low |
Do Not
Ground! |
17 |
Switched
B+ |
|
18 |
Ground |
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Logic
Board (J6/J8/J9) to Front Panel Board (J16/J18/J19):
J8 and J9 on the front
edge of the logic board are the connectors that
would normally go to the control head on MaxTrac
radios. In the MaraTrac, one single 25-pin
connector plugs into the logic board, rather than
the two smaller ones used in the MaxTracs. J6 on
the logic board connects to the RF board on the
top of the radio. The pins on this connector are
longer than normal and extend above the logic
board to accept that additional connector, which
runs to J16. J16, J18, and J19 are on the front
panel board and can be seen in the Option
Connector photo above this one. These wires are
permanently attached to the front panel board.
When viewed from the under the front of the radio
with the antenna relay at the right, J16 is
numbered left to right, while J18 and J19 are
numbered right to left. The majority of these
signals go directly to the connectors listed
above.
J6 |
J8 |
J9 |
Signal
Name or Use |
J16 |
J18 |
J19 |
1 |
--- |
--- |
9.6V |
1 |
--- |
--- |
3 |
--- |
--- |
Detected
Audio |
2 |
--- |
--- |
5 |
--- |
--- |
VCO Lock |
3 |
--- |
--- |
10 |
--- |
--- |
VCO
Modulation |
4 |
--- |
--- |
13 |
--- |
--- |
Reference
Modulation |
5 |
--- |
--- |
--- |
1 |
--- |
Volume
Control Top |
--- |
1 |
--- |
--- |
2 |
--- |
Volume
Control Wiper |
--- |
2 |
--- |
--- |
3 |
--- |
Keyway |
--- |
3 |
--- |
--- |
4 |
--- |
Handset
Audio |
--- |
4 |
--- |
--- |
5 |
--- |
Switched
B+ |
--- |
5 |
--- |
--- |
6 |
--- |
B+ |
--- |
6 |
--- |
--- |
7 |
--- |
SCI+ |
--- |
7 |
--- |
--- |
8 |
--- |
PB1
(Spare) |
--- |
8 |
--- |
--- |
9 |
--- |
PB2
(Spare) |
--- |
9 |
--- |
--- |
10 |
--- |
Ground |
--- |
10 |
--- |
--- |
11 |
--- |
Push-To-Talk |
--- |
11 |
--- |
--- |
12 |
--- |
Microphone
Audio |
--- |
12 |
--- |
--- |
13 |
--- |
Emergency
/ Hook |
--- |
13 |
--- |
--- |
--- |
1 |
TX /
Busy |
--- |
14 |
--- |
--- |
--- |
2 |
Display
Enable |
--- |
15 |
--- |
--- |
--- |
3 |
FPD |
--- |
--- |
1 |
--- |
--- |
4 |
FPE |
--- |
--- |
2 |
--- |
--- |
5 |
FPB |
--- |
--- |
3 |
--- |
--- |
6 |
FPC |
--- |
--- |
4 |
--- |
--- |
7 |
FPA |
--- |
--- |
5 |
--- |
--- |
8 |
Keyway |
--- |
--- |
6 |
--- |
--- |
9 |
5VDC |
--- |
--- |
7 |
--- |
--- |
10 |
Serial
Data |
--- |
--- |
8 |
--- |
--- |
11 |
Serial
Clock |
--- |
--- |
9 |
--- |
--- |
12 |
Ground |
--- |
--- |
10 |
Details
of Individual Repeater Controller Signals:
Power...
...is obviously required. You will need
a source of A+, between 13 and 14 Volts DC. It must
feed the big red wire on the transmit radio as well
as the B+ input of both radios. Of course, the
repeater controller will also need it. Fuses are
recommended for each device.
Ground...
...is simple. Use the big black wire coming out of
the control cable. You must also supply a ground to
the Power On/Off control line to activate the power
relay inside the radio. You will probably also have
ground via the RF coax connections. If you mount the
radios with their mounting brackets, that will
provide a ground to the chassis, but don't rely on
that connection, because you may have to work on the
radio on the bench without the bracket. Make sure
your power supply negative is also connected to the
station ground. If you end up interfacing your
controller via the RJ45 programming jack, use the
ground pin here as well.
Transmit Audio...
...from the controller can go into the MIC High
input in a variety of places, such as the control
cable connector, the RJ45 programming jack, or the
Option jack. Use a 10uF 16V electrolytic capacitor
in series with this line, with the positive end
towards the radio. Some repeater controllers may
already have a capacitor in series with their input
line.
Push-To-Talk...
...from the
controller can go into the PTT input in a variety of
places, such as the control cable connector, the
RJ45 programming jack, or the Option jack.
Receive Audio...
...to the
controller can be found in several places as well.
You can get it on the RJ45 programming jack and the
Option jack, but it's also the same signal that
you'd find on the top of the Volume control,
available at the control cable connector, the Option
jack, on J8 on the logic board, and J18 on the front
panel board. All of these are constant level,
unaffected by the control head's volume control.
This audio is also de-emphasized and the PL/DPL has
been filtered out of it, just as it is on the
MaxTracs. If DC is present on this line, use a 10uF
16V electrolytic capacitor in series, with the
positive end towards the radio. Some repeater
controllers may already have a capacitor in series
with their output line.
Carrier Indication (COR)...
...is the
remaining signal. There are several points that
change state when merely a carrier is detected:
Channel Activity and Squelch Decision on the
Audio/Squelch board for example, but if your
repeater will be using coded squelch (PL or DPL),
you will want a signal that's active only when the
proper code is received. The Audio PA Mute signal is
what I use on MaxTracs, and it already feeds the
MaraTrac's logic board, but not at a level most
repeater controllers can readily use.
The source for the Audio PA
Mute signal is on the radio's logic board,
underneath the bottom plate, under the
microprocessor shield. The feed-through hole near
the big IC has a very nice signal that's 5V when a
properly encoded carrier is received. One method of
accessing it would be to add a resistor and
transistor inverter to the logic board and bring
this open-collector COR signal to J8 pin 8 (PB1, a
spare signal), then add a jumper on the front panel
board to get the signal from J18 pin 8 to the spare
pin on the Option board (J21 pin 12) or to the RJ45
programming connector (J20 pin 2). This gives you an
active-low COR signal for your repeater controller.
Your controller will need a pull-up resistor on this
line; some units may already have one or provide for
it. DO NOT put the resistor inside the receive
radio, because if that radio loses power, it will
pull the COR line down to ground and the controller
will think there's a valid carrier present. I've
added this circuit to a lot of MaxTracs; it's
simple, works great, and avoids using the accessory
jack. See the related article on Repeater-Builder
about Simple MaxTrac Interfacing.
Another version of the Audio
PA Mute signal from the logic board feeds the base
of a transistor (Q500) on the Audio/Squelch board,
and the voltage change at that point (0V to 0.7V) is
insufficient for further use. The collector of that
transistor goes from about 2.3V when squelched to 0V
when a valid signal is being received. Unfortunately
that level is insufficient for external controller
use and as it turns the audio amplifiers on and off,
you can't load it down very much. The audio
amplifier outputs (U501 pin 4 and U502 pin 4) change
from 0V when squelched to 6.3V when a valid signal
is being received, however there's also speaker
audio present on these lines. Chances are, you'll
have the speaker volume turned all the way down at
the repeater site, and unless you run it up to an
excessive level, the audio won't bother you too
much.
I've seen a couple of
interface schemes that instruct the user to connect
Q500's collector to the Emergency / Hook line, J1
pin 18. This pin goes to the logic board where it is
pulled high, so unless you disconnect the existing
wire, you're likely to damage the audio output
circuit. I wouldn't risk it. If you free up J1 pin
18, you might as well add the two-component inverter
and get a real COR signal out of the radio.
Given a choice, I'd recommend
adding the resistor and transistor to the logic
board and bring it out to either the Option
Connector or the Programming Connector.
A
Common Interface Point:
Given the
limited number of choices and ease of access, I'd
recommend using the Programming jacks on both the
receiver and transmitter for your controller
interfacing once you add this COR signal to it. This
connector would then have signals as noted in the
table below. You would make up two RJ45 cables
between your controller and the two radios, wired as
follows. You don't need very many wires; a single
shielded pair would do nicely; connect the shield to
ground. Even flat 8-conductor network cable will do
the job, as long as you keep your cable length short
(less than a few feet).
Pin |
Signal Name or Use |
RX Radio |
TX Radio |
Notes |
1 |
Switched
B+ |
- -
- - - |
- -
- - - |
|
2 |
COR
Output |
RX
COR |
- -
- - - |
Use
external pull-up resistor |
3 |
Emergency
/ Hook |
- -
- - - |
- -
- - - |
|
4 |
Ground |
Ground |
Ground |
|
5 |
Microphone
Audio In |
- -
- - - |
TX
Audio |
Use
external isolation capacitor |
6 |
Push-To-Talk
Input |
- -
- - - |
TX
PTT |
|
7 |
SCI+ |
- -
- - - |
- -
- - - |
|
8 |
Handset
Audio Out |
RX
Audio |
- -
- - - |
|
I've used
this wiring configuration for several MaxTrac-based
repeaters and it works very well. I'd also recommend
programming the radios with identical frequencies
and making the same modifications to BOTH radios so
you can swap them around if needed.
Configuring
the Radio:
Obviously
you have to get the radio to power up, and there's
probably no reason to have a control head attached
to each one. Ideally, you would have a pair of extra
control cables from a MaraTrac, Mitrek, Mocom 70, or
Motrac. Surprisingly, these all have similar wiring
and signal/pin usage. Could Motorola actually have
standardized something this simple?
Apply +13VDC from a supply capable of handling 25
amps to the front control cable connector pins 19
and 4, and apply ground to pins 17 and 13. If you're
going to leave the top cover off the radio, you
could just solder some heavy wires directly to pins
17 and 19 (there are already heavy black and red
wires attached there) and add thin jumpers to the
other two pins. While this did cause the radio to
turn on, all I got was a ticking sound out of the
loudspeaker and the receiver did not seem to be
listening to the channel I expected it to be on.
Further investigation shows that there is no receive
audio path through the missing control head so the
radio has no audio to amplify, hence the ticking
sound. Also, the radio could have powered up on any
random mode.
Delete all modes from the radio except one. Program
that for your repeater pair. You should program both
radios with the same information.
Disable the Audible Tones (audio beeps that are
confirmation of control head button presses) on the
Radio-wide screen, otherwise any time you press a
button the audio will un-mute and the repeater will
think a carrier just came in.
Set the transmit power no higher than half the rated
output power. Set the timeout timer to 000 seconds
(and consider adding manual power control). Again,
do this to both radios.
I've read that if your radio is configured for an
advanced (A7) control head, you could configure the
radio to use the standard clamshell control head and
disconnect the advanced control head, but if you
ever reconnect the advanced head in the future, you
might "brick" the radio. I have not confirmed this.
I have also not yet successfully powered up a
MaraTrac without an advanced control head. Lee N3LEE
reports that you CAN disconnect the head and
reconfigure the radio.
One item remains: dealing with the Hang-Up Box
(HUB). This signal has to be grounded to put the
receiver into coded squelch mode. This line goes
into the control head (all versions) where it's sent
to the radio on the serial data line, along with the
other button and switch inputs. When a control head
is attached, this is not a problem as you can solder
a jumper wire from the HUB line to ground inside the
head, from pin 23 to pin 40 on the 50-pin control
cable connector on the back of the A7 head. (A
similar jumper can be added for other heads; the
wiring diagrams are in the service manuals.) Leaving
a control head connected to the receive radio may be
a "Martha Stewart Good Thing" as it lets you monitor
the received signal and even disable the coded
squelch if you ever have to. The Hang-Up line also
appears on the main radio connector J1 pin 18 and
the RJ45 programming jack J20 pin 3 (Emergency /
Hook) , so this line could possibly be accessed
without a control head present (I'll have to confirm
this however). It runs right into the Hang-up input
on the logic board.
After you
have read this page
I have made an adapter to the MaraTrac to get the
signals from inside to outside. Here is a "click" to
the page on how I did it. Ed
McKinney --- KB8QEU
Acknowledgements
and Credits:
All of the signal
information, including circuit board X-ray views
and cabling diagrams, was found in either the
MaraTrac Low Band Instruction Manual, 6880102W95,
or the M400 Service Manual, 6880901Z56; both can
be found on the repeater-builder web site as large
PDF files. Additional information came from the
MaraTrac Remote Squelch Supplement, also now
available on this web site. Verification then came
from personal inspection with test equipment.
Disclaimer:
I, Robert W.
Melster - WA1MIK, have NOT performed any of these
modifications or procedures myself, nor have I tried
to use a MaraTrac in repeater service (MaxTracs:
yes), so there may be some fine-tuning of this
article as time goes on. There may also be other
interface points that I am not aware of. If you have
additional info based on personal experience, please
let me know and I'll add it.
User Experiences:
Mark
D. Seevers - KC8QVX operates a two-meter
IRLP-equipped repeater in Jonesville, Michigan using
a MaraTrac radio as a transmitter. He reports...
There is
a QSO party on New Year's Eve and during the 2011
celebration my transmitter was up for 17 hours.
There were a few three-minute idle times but other
than that the transmitter was keyed up 100% of the
time. I mounted two four inch 12 volt DC muffin fans
under the heat sink. I used the 9.6 volts from the
antenna relay to activate a separate 12 Volt relay
to run the fans. Any time the radio is transmitting
the fans are running, and because they come on at
the start of a user's transmission it never gets
hot. I have run this transmitter for 2 years on the
New Year's Eve QSO party and it is still running
fine. I will also mention that it putting out 100
watts and giving me 70 watts out of the duplexer.
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