01/02/07

"W4XE Repeater Tech page ©"
 

The EXEC II is up to a  110W high power mobile trunk mount or a 40W desk top base station. They are available in 6 meter, VHF and UHF models. The VHF and UHF tune up to the ham band without modifications. The 6 meter 'may' take some additional work for full spec operation. They can all be modified to full duplex repeater operation. The full duplex modification is one of the easiest to perform. The 40 Watt EXEC II desk-mate makes a handy 20 Watt desktop repeater with it's built-in AC supply. It has ample room for a small uhf duplexer and controller as well. Many of the higher powered  100W mobiles have been converted to 50W repeaters.

The Exec II and MVP circuitry follows very closely to the Master II circuitry.

The main difference in the Receiver is that the Master II has two more poles of crystal filters in the IF circuit than some of the Exec II radios.

The MASTR II uses ICOMs which are temperature compensated modules. The EXEC II and MVP both use OPEN element crystal holders and the compensation is done on the exciter.. One note, the SAME crystal can be used in an EXEC II, MVP and Master II. The crystal formulas are the same.

The EXEC II and MVP share the same board layout. The Master II modular components are arranged differently. They are not interchangeable with the EXEC II and MVP.

I'll start with the GE Exec II mobile. Not as much has been published on the web about this radio as the base station.

The GE Exec II is about the easiest mobile to make full duplex of any radio I've ever converted. Three simple steps:

1.  Cut the Q905 collector lead away from the PCB.  (defeat RX MUTE and delays)

2. Jumper J904 pin 4 to pin 10  (RX OSC voltage +10 VDC on Full time)

3. Cut jumpers H7 to H8 and H47-H48 (PTT to PL encode)

You must provide a receiver antenna port connector. The original so-239 will be used for the transmitter. Remove the front handle. There are just a couple of screws.

Now drill a hole and mount a new SO-239. I used a left over GE so-239 to RCA plug cable assembly (I think I robbed it off a GE MastrII mobile).

The finished product:

If you don't have a control head somewhere you need to add a volume/squelch control. I looked around and saw that the P908 TOT timer 6 pin connector has almost all the signals you need. I used a small piece of proto board and added two 10 K pots.

The top of the SAS board:

There are a couple of wires to add to the SAS system audio squelch board for my squelch/volume mod. You have to remove the screws holding it down to get at the back side where I added the wires. You can also see the one of the two cuts necessary to a trace next to where the right side purple wire connected.

1. Cut the trace away from P901 pins 1 and 2.

2. Wire pin 1 of P908 to VOLUME ARM P901A-10. I used the H36 to H37 Jumper point.

3. Wire pin 2 of P908 to Squelch ARM P901A-12. I used jumper H10.

Now wire up the little protoboard with the two 10K pots:

I used a 6 pin molex connector to interface to the existing molex P908.

You might have noticed on the photo of the top of the SAS board and the rest of the radio there is a small PCB added below the SAS. This is a little 2 transistor buffer with led status indicator pcb of my own making. I like to buffer COS and PL detect before going off the an external repeater controller. The LED's indicate status.

CAS - J901B-7, the collector of Q923. It is active high. 0 V squelched, 7.9V open squelched.

PL DETECT J907-9  active low. 1.2V no pl detected, 0V PL correct tone detected.

I fed these signals to a 2N3904 transistor buffer through a 10K ohm base resistor. Emitter to ground. Collector tied high to +12 vdc through a pull up resistor with an led in the path.

See Below is the connector pinout for the GE EXEC II P1 control head cable:

There are a few more things to tidy up to finish the repeater conversion. Bringing out all of the repeater controller connections and wiring up the +12 VDC power to the radio.

GE  P1 control head connector:

pin 25  heavy 12 AWG red through a 10-30A fuse  and fuse holder to +12 VDC. The wire guage and fuse rating depends on your transmit power watts output setting.

pin 24 heavy 12 AWG black to power supply ground

pin 26 and pin 19 tie to pin 25

pin 17 tie to pin 24

pin 20  install a toggle switch to pull this line to ground. Channel Guard Disable

Pin 13 and Pin 14 - speaker. If you don't use a speaker you must load this with 8 or 10 ohm load.

I used an RCA connector with an 10 ohm load resistor in it. When I want to listen to the audio, I unplug the load and hook up a real speaker.

Note - keep volume low as this resistor will get hot if you have the volume turned up high as it is dissipating a LOT of wattage from the audio PA.

I utilize the NHRC-2's DB9 wiring standard for all of my repeaters. Below is my wiring from the DB9 to the GE mobile's P1.

Here is a photo of the top side of the repeater. I've added my own home brew PL high pass filter and also a TS-32. The TS-32 is used as a repeater PL encoder.

Below is the finished product. A 6 meter full duplex repeater with RC-1000 controller and Uniden uhf remote base. Usually I dress the controller cable up with black plastic spiral rap. This was supposed to be a temporary test repeater, but works so well I haven't put up the 'real' repeater a GE Mastr II.

For the GE Exec II base station, there are many excellent sites that discuss this radio for conversion to ham radio use.

A excellent starting point for conversion of GE EXEC II's are the links below:

Ray covers in-depth the conversion of a Exec II base station into a repeater:

http://www.rayvaughan.com/mastrexec2.htm

Below I've outlined a couple of the modifications I made to my own GE Exec II base station converted to a repeater.

Above shows the extra silver plated SO-239 added for the receiver cabling.  This model included the optional battery backup feature. The red/black wire and Molex connector provide connection to an external 12 VDC battery. Also at the right is the spiral wrapped cabling to an external repeater controller (NHRC-2). All of the repeater interconnect points come off of J901 inside the radio. This is a 0.156" spaced Molex connector. Digi-key has suitable connectors.

The original unit did not include the PL deck which could have been used for either the receiver decode or transmitter encode. I added a TS-32 for both of these functions. The TS-32's built-in PL audio filter was used to filter out the user's PL before the transmitter regenerates it. The COS and PL detect levels were not in accordance with my 'standard' I use. I added a small perf board to invert COS to provide an active LOW to the controller. I also inverted PL detect to provide an active HIGH to the controller. In this case I had to tap onto the TS-32 IC for a convenient signal point. It's transistor circuitry was tied up with the 'audio-mute' circuit, so I couldn't use the OUT1/OUT2 transistors.

Conversion of the radio to full duplex for a repeater is a breeze. You just cut and lift up one side of diode CR906. Then jumper the collector to the  emitter of Q908 on the SAS System-Audio-Squelch board. A manual with schematic is handy at this point. See Ray's site.

A view with the top off of the radio. The RF drawer slides up for easy access to the radio's circuitry. A built-in AC to DC power supply is housed on the right side of the cabinet. I highly suggest you de-rate the power output of the transmitter for Repeater duty by 50%. The internal DC power supply isn't meant for heavy duty repeater use either. I recommend you mount an AC fan to blow on the PA and Power supply heat sinks.

If you want an off the shelf ready to plug in Exec II repeater, MCC (makers of the RC-100 and RC-1000 repeater controllers) does an excellent job. Especially nice is his front panel interface and new audio filtering board:

http://home.earthlink.net/~mccrpt/geweb.htm

Note: click on thumbnails for enlarged photos!

73's Ralph W4XE

01/02/2007