Back to Home
An Overview of the GE
(or whatever corporate name is in use today)
MLS Mobile Radios
By Robert W. Meister WA1MIK
The MLS radios are 2, 8, or 16 channel synthesized mobile radios, similar to the Motorola MaxTrac products. They come in VHF-low, VHF-high, UHF, and 800 MHz models with 30-40 or 60-watt power levels, depending on the band. 8 and 16 channel radios can be equipped for scanning. They are identical to the MLS-II radios in just about every aspect except for the programming interface and procedure. If you haven't already read the MLS-II Overview, now would be a good time to do so. This article covers just the MLS radio and how it differs from the MLS-II models.
This overview is based on personal experience with what turned out to be an MLSH040 VHF-high radio (2-channel, 150-174 MHz). I thought I was purchasing a non-working MLSU241 UHF radio; that's what the model number sticker said, however upon opening the radio it was obviously NOT an MLS-II nor was it UHF. It didn't work and it was very dirty inside and out. It might have been under water or stuck in the mud at one point in its lifetime.
Differences Between the MLS and MLS-II Radios:
The MLS-II does both Channel Guard (analog tone or CTCSS) as well as Digital Channel Guard (digital coded squelch or DCS). The MLS only does Channel Guard (analog tones).
Both radio series have the same channel and scanning capabilities and share the same accessories. The MLS radio has separate boards for the receiver and transmitter; the MLS-II radio combines this functionality onto one board. The MLS radio has two boards that make up the system control / synthesizer functions; the MLS-II radio puts all of this onto one board. The circuitry and specifications are essentially identical; they're just arranged differently.
The MLS radio requires an external programmer and unique cable, which reads and writes the radio's EEPROM; the MLS-II radio uses an ordinary PC-compatible computer and a serial interface, similar to Motorola's RSS and RIB setup, and talks to the radio's microprocessor, which reads and writes the radio's EEPROM. You can immediately tell which radio you have by checking the last digit of the model number string: '0' for the MLS and '1' for the MLS-II.
Accessories, Features, and Other Observations:
The microphone and programming cable is the same as on the MLS-II. The pin-out of this connector is listed in the table below. Pin 8 is closest to the outside edge of the radio. Pins 2 and 7 are also used by the programming interface cable.
|Pin#||Signal or Use||DCV||Notes|
|1||Speaker High||- - -||Always active|
|2||PTT / Clock||+5.0||Ground for Transmit|
|3||Mic Low (Ground)||0.0|
|4||Mic High (w/Bias)||+9.5||Approx 80mV/kHz|
|5||A- (PTT Ground)||0.0|
|6||Speaker Low / Reset||- - -||Selected by internal jumper|
|7||CG Disable / Data||+5.0||Ground for carrier squelch|
|8||Store||- - -|
The front panel circuit board on the MLS radio has the same functionality as the one on the MLS-II, but all of the LED signal lines are inverted. The pushbuttons are wired the same though. This means you can't just swap front panels between these two radios.
The choice of internal or external speaker is made with a jumper on the SysCon1 board. It routes ground to either the internal speaker or the MIC connector pin 6.
The scanned channel selection is only done via the front panel. The MLS-II retains this info when the radio is powered off or unplugged. As my radio didn't have scanning and I have no way to program it, I don't know if the scan list is completely erased when the radio is reprogrammed.
My radio was programmed with 218.1 Hz Channel Guard tone. The tone decoder, with 700 Hz deviation, had a ± 3 Hz acceptance window, i.e. it would decode a 218.1 Hz tone anywhere from 215.0 Hz to 221.0 Hz. This is about 1.5%, the same as on the MLS-II. The lowest level it would reliably decode this tone was 200 Hz deviation. The acceptance window at that level was ± 2.5 Hz. The MaxTracs I've tested will often decode PL with deviation as low as 50 Hz. Nominal CTCSS deviation for wide-band (5 kHz) systems would be 500-1000 Hz.
The radio is programmed via the microphone connector on the back of the radio. The radio's signals are TTL levels; a suitcase programmer and cables are required. I have seen various people offering to program MLS radios but I haven't talked to any to find out more details. Eventually I borrowed a TQ2310 suitcase programmer; my experience is detailed at the end of this article.
After getting the radio to turn on, my VHF-High radio output 40 watts, drawing 11.0 Amps at 14.0 Volts. The frequency was less than 100 Hz low on the channel I measured. Sensitivity was better than 0.35uV for 20dB quieting.
Issues With This Radio:
Initially, the radio would not turn on. In fact, it drew 60mA when I first connected power to it, but this dropped to 20mA after several minutes.
There was a pigtail wire for an external speaker connected to the internal speaker. I removed this and rewired the speaker to its connector.
Several screws are missing from the SysCon2 board. A few other screws had bad threads (M3x0.5) but I retapped and cleaned them.
I thoroughly cleaned the radio by taking the control head off and stripping it down to its individual parts. Plastic parts were washed with a household cleaner and hot water. Alcohol and a toothbrush were used on the silicone membrane keypad. I washed the entire chassis with hot water and a brush to get the mud off it. I dried what I could reach, blew hot air at everything else, and let the radio dry for a day before trying it again. No real improvement; it still wouldn't turn on, so out came the schematics.
I noticed two leaking capacitors on the SysCon2 board (to the right of the heat sink) and I replaced those. I will probably replace all the electrolytic caps soon as others are showing similar signs.
I started by following the power button signal, which was sitting at 1V and it should have been 5V. Eventually I found about 20,000 ohms of resistance from that line to ground even with the control head disconnected, so I pulled the entire SysCon1 board out and washed it twice with isopropyl alcohol. The entire board was coated with some sort of resin that softened with alcohol. Vigorous scrubbing got rid of most of it. The resistance increased to over 1 megohm, but it still wasn't infinite. Nothing is attached to that line except two connectors: one from the front panel and one going to the SysCon2 board. I traced the problem to some kind of crud buildup under the 32-pin connector that the SysCon2 board plugs into. After reheating several pins and feed-through holes, the problem cleared up. The resistance to ground measured infinity, and the radio would power up, drawing just over half an amp when turned on.
I could hear squelch noise and the volume would go up and down, but the volume was very weak. I suspect more bad capacitors on the SysCon2 board. I could only select channel 1; it turned out that channel 2 was blank.
Follow-up: I replaced two 47uF 16V caps around the audio amplifier IC and that fixed the low volume issue. A week later I replaced the remaining six electrolytic capacitors on the board. Several showed signs of leakage but they all measured OK and new ones didn't seem to make any difference in the operation of the radio.
I connected a wattmeter and dummy load, plugged in a microphone, and pressed the PTT button. I was rewarded with 40 watts on 154.569900 MHz. Deviation was 4.5 kHz with 700 Hz CTCSS deviation. I increased the total deviation to 5.0 kHz, kept the CTCSS at 700 Hz deviation, and adjusted the master oscillator to bring the frequency up to 154.570000 MHz. Sensitivity was around 0.35uV for 20dB quieting and the squelch opened below 0.2uV with or without CTCSS tone.
What's Under the Hood:
(References to upper, lower, top, bottom, left, or right, are as the images/photos are viewed on your screen.)
Loosen two screws at the rear and remove the top cover to get you to the system control / synthesizer (SysCon) boards. The upper half, under the cast aluminum shield, contains the VCO and transmit audio circuitry. The SysCon2 board plugs into the SysCon1 board.
You have to remove the SysCon2 board to get to the rest of the SysCon1 board, which has the microprocessor, program memory, user personality memory, and support circuitry. The front panel cable, seen folded at the left side of the image, plugs into the SysCon1 board. The internal speaker jack and jumper to select internal or external speaker are along the lower edge, below the EPROM (the IC with the yellow sticker). Two cables feed control signals to the circuit boards on the other side of the chassis. The model number of the SysCon1 board is CMC-386.
The SysCon2 board, shown below, has the power supply regulators, the on/off logic, and the loudspeaker amplifier IC603. Note the four 47uF 16V capacitors I've replaced already, just to get the radio working; the rest were done a week later. The model number of the SysCon2 board is CMC-405.
Loosen two more screws at the rear to remove the bottom cover to get you to the transmitter (right) and receiver (left) boards. There are pots here for squelch and output power, also well labeled. The receiver front end, RF amplifier, and pre-mixer filters are under their own aluminum shields. Coax cables route the antenna signal to the receiver board. The model number of the receiver board is CMA-257.
The copper shield covers the RF driver module and the entire RF power amplifier. All of the power leads are easily detached. Two flat cables and two coax cables connect these boards to the SysCon1 board on the other side of the chassis. The model number of the transmitter board is CAH-281.
The model number of the two-channel front panel circuit board (not shown) is CMD-318.
There's one "combination" manual for each band, which lists the individual major assembly manuals. Each major assembly (SysCon boards, transmitter, receiver, and front panel) has its own manual (LBI), depending on the frequency band of the radio. There are also frequency-dependent service manuals that cover maintenance and alignment, as well as installation and operation manuals. The only LBIs I could find covered the VHF-hi model, which is what I have. The quality is rather poor.
Rather than transcribing existing work, here's a link to a page that lists all the manual numbers; it's part of the Doug Hall Electronics web site. Many of the manuals can also be found in the GE section of Repeater-Builder.
This radio requires a TQ2310 suitcase programmer. I was able to borrow one - without an MLS-specific manual, of course - and with some difficulty I managed to reprogram the radio.
I discovered that the programmer knows the VHF radio can only go down to 150.8 MHz, but by hitting the INSERT key instead of the down-arrow key, a lower frequency could be forced in. After selecting the channel, you are presented with fields for the transmit frequency, transmit Channel Guard frequency, transmit CG Squelch Tail Elimination (STE) Y or N, then identical fields for receive, and finally the Carrier Control Timer (CCT) Y or N. You go through this for all channels. There doesn't seem to be a way to specify how many channels the radio should have; I was able to cycle through 10 channels this way. I guess they "leave that to the student." When I finished data entry for my two channels, the program warned me that the transmit frequencies were more than 6 MHz apart and that the receive frequencies were more than 3 MHz apart. I accepted (and ignored) both warnings and continued.
In another screen you get to select the CCT value in increments of 30 seconds, and whether the radio's front panel LEDs should be active during scanning (for those radios that are capable of scanning; mine wasn't) or not. Finally you get to write the data back to the radio, which only took a couple of seconds. The data was automatically verified for me too. The radio worked fine on its new frequencies and I can now select either channel 1 or channel 2.
The programming software allows you to do other things as well, such as copy data from channel to channel, but I didn't go through them. This particular TQ2310 was capable of programming dozens of different radios; I only needed it for my MLS radio.
This was my first and only experience with any suitcase programmer (GE or Motorola). I'm pleased to say that I'd much rather use the IBM-PC programs and interfaces.
Acknowledgements and Credits:
Doug Hall's site seems to have the most information on the MLS radios. Highly recommended.
Channel Guard, CG, and DCG are trademarks of Harris / MA/COM / GE / Ericsson, Inc, or whatever they're called these days.
RSS, PL, DPL, and MaxTrac are trademarks of Motorola, Inc.
The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.
Back to the top of the page
Up one level (GE index)
Back to Home
This page originally posted on Thursday 10-Mar-2011.
Photographs, article text, and hand-coded HTML © Copyright 2011 by Robert W. Meister WA1MIK. All photographs were taken by the author.
This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.