GE MVS Mobile Radio - Information & Modifications
A full list of LBI manual publications for the MVS radio, parts and accessories can be found here. We don't have all of them, but most of them are there.
The LBI sections you will need to build the manual for your MVS radio depends on whether you're a user or a tech and if it is VHF or UHF. The list below is in LBI number sequence. Radio users will only need number 7. Bench techs will need numbers 4, 5, 12 and 15. Bench techs will also need either: 1, 2, 3, and 6 for VHF radios OR: 8, 9, 10 and 11 for UHF radios. Radios with the remote (trunk) mount option will need number 13. Desktop base stations will need number 14.
Most of the MVS radios that you will encounter have 16 channels. Some of them only have 2 and a very few have 128 channels. The most common way that I have discovered to find out if your radio has 128 channels is whether or not it has a "mode" button on it. If it doesn't, than you deffinetly have a 16 or 2 channel radio. VHF radios produce 40 watts of power. UHF units produce 25 watts.
The Microphone & Mic Connector
The MVS implements the tone squelch mic clip hangup feature by using a microphone that has a reed switch mounted inside the back of the microphone case, and a permanent magnet mounted in the GE-supplied mic clip that is mounted on the dashboard. When the user lifts the microphone out of the clip the reed switch changes the receiver mode from CG mode to carrier squelch mode. The microphone clips with the built-in magnets are almost impossible to find in the second-hand marketplace. If you have a mic for one of these radios, great, they work fine for repeater/simplex voice use. The special mic hooks are rather hard to find, so to force the mic to stop the on/off-hook silliness, open up the back of the mic and clip the blue wire that goes to the little switch area at the back of the mic. It will make the radio think that the mic is always on-hook.
The mic connector has the same functionality as the option connector. Pins are shown in the photo below. Be careful. Shorting certain pins with power on will blow the internal fuse.
Programming Info & Notes
The MVS uses the TQ-3310/TQ-3370 programming interface (RIB) and the TQ3315 (p/n 19B801417P4) programming cable. The radio has an 8 pin EEPROM which is serially programmed using an old DOS based computer. The programming cable connects through the microphone jack. (Here is a pinout for the programming cable.)
Each channel will have entries for: TX frequency, RX frequency, CG TX (PL), CG RX (PL), STE TX / RX and CCT. This translates to transmit RF frequency, receive RF frequency, transmit tone frequency, receive tone frequency, STE (y/n), and a numeric value for CCT. These units are synthesized with programmable PL or DPL.
Note: Should you want to input a frequency that is out of band, using the key combination of CTRL+E will allow you to do this from within the DOS programming software.
How to Open the Radio
Most of these mods are found on the bottom side of the radio. To access it, flip the radio over, and remove the two screws at the front of the metal plate. Simply flip the plate off, and expose the pc board.
The low-power mod, and the adjustments are on the top boards of the radio. This plastic cover snaps on at the side of the radio, near the back. Gently pry the sides out with a screwdriver, and pop it off.
The Option Connector
Inside the radio at the back where the power line connects is an "option connector." This 13 pin connector allows you to easily hookup input, output and switchable power to run TNC, APRS, and EchoLink functions with this radio. On the System Board, you'll see a row of 13 pins. They are shown in the photo below, with the relevant pins labelled. The manual shows all pins and their purpose.
There are several trim pots on the top side of the radio offering adjustments, as indicated in this photo:
Low Power Modification
While the power output is fixed, a quick modification allows you to reduce it as low as five watts for QRP operation. This is also useful if you plan to use this radio as a base station to access a local repeater.
This is the topside of the radio, at the back. Modifying the jumpers as described in the photos below will reduce the power output from 40 (or 25) watts down to 10 watts. Backing off the trim pot (see adjustments above) will further reduce output to 5 watts.
The Ignition Sence Modification
Open the underside of the radio. Clip the red power lead about two inches from the board. Strip a little insulator off, and solder the red wire to the topmost (in the picture) lead on the regulator. This simplifies your electrical hookup.
The Little Green Fuse
Open the underside of the radio. To the right of Q903 mosfet, you'll see what looks like a green resistor. (It's already removed in the picture.) It may or may not have resistor-like color bands. On the board it's labelled F901. It's not a resistor; it's a fuse. Chances are, before you finish all these mods, you'll blow it. When this fuse blows, it shows no visible signs. Check it with an ohm meter for continuity if you suspect it has blown.
I have found these fuses hard to find, and annoying to replace. So, I replaced it with a fuse holder. Remove the fuse, and solder short leads of wire to each hole. Solder a fuse holder to these leads, and insert a 3 amp fuse. Alternatively, one lead of the fuse holder may be soldered to the center lead of the mosfet. All my MVS radios are in fixed locations. If you are using your radio in a car, you may want something a little more robust than that, but you get the idea.
(The photo ingition sense modification photo above, shows the F901 fuse quite well.)
Data Packet Usage
Since the MVS is not easily programmable for most people, it is not nearly as frequency-agile as a typical 2m ham radio, thus using it for voice is alright, as long as you don't ever need to change to a freq that isn't programmed into the unit. This is where this model shines for data. The MVS units are particularly suited to data/packet use, mainly APRS, but also Winlink and traditional packet. Some guys even use them as simplex IRLP nodes. With the 2-channel model, you can program one for 144.390 and the other for the "backup" APRS freq of 144.340, or whatever else you see fit. Using this radio as an APRS tracker works great, costs a bunch less that most any ham radio.
If you are running a TNC or interface (like a SignaLink) that requires power, connect - to #1, and + to #5. Audio to the radio is #4. Ground it to a screw on the board.
Audio from the radio is #3. On some GE-MVS radios, the audio level from pin #3 is fixed. On others, however, it varies depending on the volume setting of your radio. If this is the case with your radio, set the volume level where you want it for proper audio levels into the computer, and leave it.
The MVS volume setting does not go down to 0. Sometimes it's practical to wire a switch that bypasses the speaker and runs the audio through an 8 ohm resister to create a mute function. The manual indicates that to create a mute function, solder a switch that shorts #10 to ground. When #10 is shorted to ground, the speaker is muted. Output levels to #3 are not affected. However, #10 works as a COS indicator, which is useful in many applications. (#10 will go to +5vdc when a signal is received.)
Remote Base & Repeater Usage
Here are a few things to remember if you plan to use this radio for a remote base. Should the power go out, the radio remembers which channel it was on and returns to that channel when power is restored. The MVS has a push button on/off along with a digital volume pot control. The volume is an up/down push button and the LCD shows the level of volume on a bar graph. The standard top of the volume pot volume-squelch-hi discriminator audio is available. There is also a point to tap the output of a de-emphasis and high pass audio filter. The amplitude is a little hot, so you might want to attenuate it with a pot before sending this to your repeater controller.
There are some more interesting access points inside the radio on J905 and J703. A main point needed for any remote base or repeater project is the receivers activity indicator. This is usually called COS, Carrier operated Squelch. The MVS provides several locations for this signal. With AUDIOMUTE* and no RX signal present the signal will be close to zero volts DC. With an RX signal the output will be close to 5.0 VDC, a TTL level logic signal. If the channel is programmed for carrier squelch only, this signal will go High (5 VDC) on any signal on the channel. If the channel is programmed for Channel Guard (PL/DPL/CTCSS) required then only a signal with the proper tone(s) will unmute the radio and cause AUDIOMUTE* to go high. For a channel guarded memory this in effect becomes COS+PL, or COS AND PL. It requires both to be TRUE for the signal AUDIOMUTE to go ACTIVE HIGH. If you require a separate COS detect only no matter what the PL is doing, there is a classic GE signal called CAS or Carrier activated Squelch on J703. It will go active high on any signal present at the receiver. Having separate COS and PL detection signals is handy if you want to remotely turn off any PL requirements in a repeater application.
A note of warning: the COS signal(s) you tap off of in the radio are TTL logic signals used by the internal microprocessor of the radio. They do not have a high drive level that may be required by your external repeater controller. Hooking up the controller may damage your radio permanently or at least cause it to malfunction whenever you load the line down. I would highly recommend you feed the AUDIOMUTE signal into a transistor buffer. Tie one end of a 10K ohm resistor to AUDIOMUTE. Tie the other end of the resistor to the base of a 2N3904 transistor. Tie the emitter lead of the transistor to Ground. Tie the collector of the transistor to your repeater controllers COS for the remote base. Upon a signal detect, the collector will pull down to ground for an ACTIVE LOW COS detect. Your controller may need you to pull this collector signal line up with a 1K resistor to +12VDC so that a voltage is present to indicate NO activity. If the controller needs an active High COS, just add another transistor after this one to invert the signal.
A mobile radio is designed for a low duty cycle transmit. For repeater or remote base applications this will stress the radio's RF final PA. The heat sink assembly is not big enough to keep the transmitter cool and the radio will overheat. You must always turn down the power output and provide external cooling.
Remember to derate the mobile output power if you are going to use them in a repeater application and run some kind of a cooling fan!
|Last Updated on Wednesday, 07 September 2011 07:51|