N3CRK System M-230 Repeater

Long since retired!


The radios I set up my first 220 repeater with were "System M-230" available on eBay. They are Chinese made radios. I can't really recommend them. They aren't that great.
There is only one seller. Out of four radios I bought, one was bad. To give him credit, he offered to replace it but it would have cost me $67 to ship it back.
It wasn't worth it! They are rated at 5/10/50 Watts. I measured two radios, they were 10/30/37 watts. There is one knob for a multitude of functions.
the radio is neither intuitive nor user friendly. I had to make up a cheat-sheet just for basic funcions...like volume, squelch and output power.


Here is how I built the repeater

The first step was to buy two antenna adapters from eBay - Male miniature to SO239.
These are needed to connect coax with PL-239's to the radios.
Either style will work. I used the straight ones for the repeater and the cable style after I retired the radios as mobiles.

The next step was to buy adapter cables for the two radios to bring out Receive Audio, COR, Transmit Audio and PTT. These are available on eBay.

This is where they plug into the radios. They exit under the power wires.

Here is the pinout of the cable's DB-9F.

1 - Receive Audio Out
2 - Transmit Audio to Modulator
3 - COR Out
4 - Push-to-Talk In
5 - Ground

Don't forget to buy two DB9 solder type males and hoods.

Here is the actual 12 Volt, 20 Amp power Supply I used for the transmitter. These are readily available on eBay.

I used an old Heathkit 12 Volt power Supply for the receiver.
For back-to-back radios the 20 Amp power Supply would easily power both.
I also bought mating power connectors to make up short power cables. One could certainly cut down the cables supplied with the radios.
When I retired the radios as mobiles though, I was glad I saved the original cables.

From here on out it got much more complicated because I used a split site with receiver and transmitter about 150 feet apart in different buildings and antennas on different towers.
For lighning protection I used transformer balanced audio pairs and reed relays for Push-to-Talk.

I have every reason to think if you connect the radios back-to-back you will have a working repeater.
I used my favorite controller, the Ham Gadgets ID-O-Matic IV. It is only $39.95 for the kit or $59.95 built.
With DB-9M's wired to it, it worked perfectly with these radios.

I am sure with the pinout above and two DB-9M's it should work with any controller.


Here is the front of a male connector that plugs into the adapter cable on the M-230.
Once I have positively identified pin 1, I make a mark with a black sharpie front and back so I don't get confused when I wire it.


Here is the back of the male connector on my transformer/relay box.
Pin 5 - (Shield) Ground (with a piece of the stripped jacket as spaghetti.)
Pin 4 - (Black) Push-to-Talk (Ground this pin to transmit)
Pin 2 - (Red) Transmit Audio to Modulator


Here is the wiring on my transmitter transformer/relay box.
The shield from the DB-9M connects to pin-1 of the audio transformer secondary, the ground and internal shield on the transformer (this pin is also grounded to the case.)
The red wire connects to pin-6 of the transformer secondary and carries audio to the modulator.
The Black wire connects to the reed relay which ground the Push-to-Talk to transmit.
The green wires from the primary of the transformer and the red wires from the relay coil connect to a barrier strip on top of the box.


Here is a test jig for testing each radio on the bench.
(From left to right)
Pin 5 - (White) Ground
Pin 4 - (Black) Push-to-Talk (Ground this pin to transmit)
Pin 3 - (Orange) COR from the receiver (Goes low on open squelch)
Pin 2 - (Red) Transmit Audio to Modulator
Pin 1 - (Yellow) Receive Audio


By the way, when you wire these you must use a small iron filed to a needle point.
(It's clamped in the vise for the photo.)

I also like to plug it into a connector of the opposite gender to act as a heatsink and to let me clamp them firmly in a vise without bending the tabs.

Whenever I have to throw away a bad computer power supply, I always cut the wires from it. As you can see, they make excellent hookup wire.


The radio under test connected to an Astron 10 Amp power supply


First test: (Receiving while transmitting on my HT, no antenna on M-230)
Audio from speaker - YES
Audio on the 'scope connected to pins 5 and 1 - YES


Voltmeter connected to pins 5 and 3

(Squelch closed) 4.96 volts - GOOD


(Transmitting from HT) 8.2 millivolts - GOOD
COR working - YES


Connect SWR meter and dummy load
Gound Pin 4 - (Black) Push-to-Talk



Red Transmit light is on - GOOD

Surecom SW102 Shows:
3.50 Watts - Radio is transmitting on low power
223.500 MHz - Radio is on 220 Simplex
SWR into my dummy load is 1:1
Forward power is 3.50 watts
Reverse power is 0.00 watts
Transmit - GOOD


Here is a crude modulation test using only the HT (You may have to turn the volume up some.)
Touch Pin 2 - (Red) Transmit Audio to Modulator - You should hear a slight hum from the HT
Wrap your other hand around the AC cord to the power supply - the hum should increase
If you get these results, the audio input to the modulator is basically working.