The GE MVS radio is easily available on e-Bay for under $50.00. The two channel VHS models are most common, but you can also pickup 16 channel models with scan, and UHF models. Typical output is 40 watts. 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.
While the power output is fixed, a quick modification allows you to reduce it as low as five watts for QRP operation. I've done this on two of my radios that are used only to access the local repeater.
You will need to locate or build a programming cable and software, or pay the price to have it done. Other than that, you'll find this a sound radio for these applications.
Download the original GE MVS manual here. This will provide operating information, and in-depth background to the mods shown here, including block diagrams and schematics.
On the bottom of the radio is a silver tag with "COMB" then a number/letter sequence, and also "SER#" and a number/letter sequence. There is also some FCC data. What we're concerned with is the "COMB" data. This will tell you the band, frequency range, power output, number of channels, etc. The Hall Electronics website has a complete chart, so I won't repeat it here. Note that many eBayers selling MVSs don't know what they have, so get the combination number off them and find out for yourself before bidding.
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.
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. Note F901, the little green fuse. It is discussed further below.
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 this picture.) It may or may not have resistor-like colour 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 centre 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 mod photo, above, shows the F901 fuse quite well.)
If it applies to you, there's an easy mod that reduces the power output on the radio. 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 watts to ten watts. Backing off the trim pot (see adjustments below, will reduce output to five watts.
There are several trim pots on the top side of the radio offering adjustments, as indicated in the photo.
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.
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. Travis, AA9NV, reported to me the following: "I fought with audio for three days assuming pin # 3 audio was wide open audio and thinking something was messed up with the tnc or such when all I had to do was turn up the volume. I connected the MVS to my HP service monitor and sure enough, the audio goes from very weak to multiple volts by the time it hits the half way mark connected only to pin # 3, no other audio was connected." 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. For more information on this, go to my IRLP wiring page.
The MVS volume setting does not go down to 0.which is I've rigged 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.)
Click here for IRLP wiring instructions.
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.
There are other good GE-MVS sites, namely:
Thanks to Scott, VA3EXT for all his help teaching me many of these mods.
Last update: 10-Apr-2010 7:48 AM Web page by: Warren Paulson |