Step by Step procedure for duplexing the GE Custom MVP

Step by Step procedure for duplexing the Custom MVP®
By Kevin Custer W3KKC

Build a Repeater from a GE Custom MVP
HF, VHF, or UHF units can be converted to repeater.
Read through this entire procedure before beginning.

General: The G.E. Custom MVP is a crystal controlled, under dash mounted, commercial two-way transceiver closely related to the MASTR II and MASTR Executive II series. Compared to the other two models, the MVP is the smallest of the 3 measuring only 3.5" H x 8.4" W x 11" D, including all projections & heatsink on the 35 watt model. The MVP typically comes in a 5, 20 or 35 watt model. Although this article shows pictures of the UHF model, the duplexing instructions also apply to the HF and VHF models as well. The 66 suffix model is spec'd for 150.8-174 MHz but will tune down to the 2 meter ham band without modification and have reasonable sensitivity. The 88 suffix is spec'd for 450-470 MHz but will tune down into the UHF ham band without modification and have reasonable sensitivity.

This conversion was written primarily for the installation of the NHRC-4/MVP controller custom made for the GE MVP.

The GE Custom MVP makes one of the nicest portable, compact, rugged, and cleanest repeater projects you will see.

GE Custom MVP Radio Set

Forward: This modification is not for the faint-hearted. Although the MVP® mobile radio system is one of the easiest of the commercial mobile radios to convert to a repeater, you should be sure you are very comfortable with the operation of the radio before you attempt this modification. A thorough understanding of the way the MVP® radio and control system work is absolutely essential for the success of this conversion. A manual is not necessary, but is desired for comprehending the conversion and tune-up; that being said, support for your MVP conversion may be available from a few resources.

These resources are listed below:
GE MASTR II/MVP Email List.
Repeater Elmers.
Email support from the author of this article.

Disclaimer: The Author nor NHRC assumes any liability for any damages to your Custom MVP radio set or any associated equipment from your inability to perform these modifications. If you have any doubt about your ability to correctly modify your radio or to install the repeater controller seek professional assistance. Damage to your MVP or NHRC-4/MVP controller due to improper radio modification, improper installation, or improper hookup of the controller is not covered under any warranty.

Choosing a radio to convert: These links will help you determine what you have or what you are about to buy:
MVP Radio Combination Numbers (Nomenclature) from Hall Electronics
MVP Transmitter ID Numbers from Hall Electronics

Concept: Some of the information in this article was gleaned from the NHRC-4/MVP manual as there are instructions contained within it to help convert the MVP to a repeater. The information being used in this article from NHRC LLC is being done so with written consent.

The following instructions are provided to help convert a General Electric Custom MVP mobile 2-way radio to a repeater station. Modification of the SAS Board and Rear Panel, for addition of a second antenna port, allows the radio to operate full duplex. This modification is intended for those who are using a newer type controller which provides a means of muting and de-emphasizing the audio of the receiver. NHRC controllers provide both functions; therefore an additional interface board is unnecessary. This modification was written primarily for the NHRC-4/MVP controller, however, the instructions can be followed to attach any controller. The /MVP suffix refers to a type of controller which bolts into the MVP, in the spot formerly occupied by the original Channel Guard (CTCSS) board. The /MVP controller allows for a clean, slim line repeater to be fashioned, with all support being contained within the chassis.

Front view of MVP with NHRC-4/MVP controller installed.

Before you begin, a word of caution: The first thing to do is ensure your MVP is tuned up and working. If the unit is being converted to the ham band, make sure the radio works properly in its original band and split before any modifications are made. This will allow you to repair any problems first, which could result in really getting lost. Afterwards, retune the radio to the ham band before any duplex modifications are made so you will know what to expect as far as transmitter output power and receiver sensitivity are concerned. The use of the power cable and microphone are necessary to insure the radio is operating properly. Borrow a cable assembly from a friend or visit the local 2-Way shop and see if they will test the radio set for you. Alternately, use the information below to power the radio and use the mike connector image to ground pin 3 as to key the radio so you can test the transmitter. In actual repeater operation, a local microphone is not needed, and these instructions don't allow for the connection of one. Some of the information in this article is from hyperlinked pages removed from this site. You may need to use your browsers "Back" button to return to this article.

Powering:

Rear Power and Speaker Connector Pinout Image.

Mike Connector:

Mike Connector Pinout Image.

Procedure:

If you haven't already done so; test your radio on the frequency it is currently tuned, then, re-crystal your channel ICOM's (crystal oscillator module, or channel element) to your repeater frequencies. This is done by either sending the ICOM's to a reputable crystal house or getting replacement crystals and installing them into the elements yourself. Retune the radio to the new frequencies by using a 'Test Set' or analog (needle type) VOM and the

tuning instructions here.

Start the conversion by disassembling the radio set, which is done by removing the outer cover which is held on with a nut on the back of the radio set. Remember how you take the radio apart so you can get it back together as it was. Next, remove the four screws that hold the front panel in place. This allows you to get to the SAS and (if installed) Channel Guard board.

If installed, remove the Channel Guard (CG) board. This board is the smaller of the two, located next to the SAS board and can be identified by its lack of connectors. Unplug or cut off any connections from the CG board to the SAS board or wherever they may terminate. This includes all wires that plug in or otherwise get connected. Also, unplug the CG encoder cable (shielded wire) that runs from the CG board to the exciter. You will likely have to cut the rope loom that tailors the cabling. You may want unspring and keep the terminals and wires from connectors for re-use as they come in handy when interfacing the needed repeater signals to the radio after all of the duplex modifications have been performed.

Do the duplex modifications to the SAS board as described on this linked page. This step is necessary to allow for simultaneous transmitter and receiver operation. This is done by defeating and strapping the receiver oscillator always on and disabling the receiver muting circuitry.

After doing the SAS Board modifications go back over your work then replace the SAS Board back onto the front of the chassis. Use caution when replacing the board so the mounting tabs of the audio IC and the transistor insulators get seated back into their proper position.

Now re-connect the two plastic connectors back onto the SAS board. There will be 2 individual wires bundled along with the smaller connector that need to be plugged into the SAS board. One of these wires may have been connected to the CG board if originally installed, however it will now be plugged into the SAS board. This one (may be Gray or Blue in color) is now plugged onto the single vertical pin near J905 pin 7 as shown in this SAS connector detail image.

The other wire (usually yellowish in color) is plugged back onto its original location; the single vertical pin at the opposite corner of the board as shown in the bottom of this picture with the NHRC controller installed.

If your radio has an orange lead from the front panel Squelch Switch, cut off or tape this lead as it is no longer required.

Re-test your radio for proper operation. It should receive and transmit simultaneously. If it doesn't, now is the time to fix anything that may have gone wrong with the modification before you proceed.

Add the receiver antenna connection as outlined on the linked page.

Deal with the T/R Relay (or not?)

Install the NHRC controller and CTCSS decoder as directed in the controller manual. We use the Com-Spec TS-64DS board for the CTCSS, PL, CG or whatever you want to call it, and stick it to the front panel as shown in this image.

Make note of the next 2 steps as you have the option to do it that way NHRC states in their manual, or a different way I suggest.

I suggest you connect the controllers B+ power differently than what is suggested in the NHRC manual. I prefer to power the controller from 13.8 volts instead of 10.0 for technical reasons. I simply supply the controller with power from the B+ lead (J906 pin 6) on the SAS board as shown in the connector detail image below.

I also suggest you run controller transmit and ctcss audio directly to connector P902 on the exciter. I remove the original pins and wires from the connector and re-use the pins on new interconnecting wires. The exciter connector detail shows the connection of the TX Audio and PL Audio to P902.

Install a PTT Disable Switch. This switch can be easily installed by inserting the switch in series with the PTT signal from the controller to the radio set. The front panel is a good place to physically mount the switch. A momentary push button switch can also be placed and wired to enable the transmitter for testing (momentary PTT test switch). We wire the PTT test switch through the PTT disable switch so you cannot make the transmitter operate at all unless the PTT Disable switch placed in the Operate position. Connection of the PTT signal from the controller to the radio terminates at H17. The SAS connector detail image also shows this location, H17.

Cut a slot in the top of the front panel to gain access to the control pots on the NHRC-4/MVP controller as shown in the potentiometer cut-out image.

Replace the front panel onto the radio chassis using the 4 screws being careful not to pinch any wires.

Add a length of quality power cable to the radio and terminate it with the connector(s) of choice that mates with your power source.

Set levels and program your controller.

Place the cover back onto the radio set.

Either terminate the speaker connections (SKR HI and SKR LO) with a local speaker (jack) or a load resistor so the audio amp doesn't oscillate. A local speaker is nice to allow you to listen for desense. Refer to the first link under the "Powering" section for connection to the speaker terminals.

You are done!