KB8ZQZ's Syntor X packet conversion page

This page discusses turning a Syntor X into a data radio. That's a bit of a misnomer; the radio has most of the support it needs to transfer data built in from the factory, since it was designed to do digitally encrypted voice. What we must do is enable the functionality which is already there. It's important to note that the material here assumes you are using a VBJ model radio, which was not factory configured for encryption. If you have a VXJ, the process is a little different. See Mike Blenderman's site (link below) and/or the Motorola manuals if you have a VXJ.

The process of configuring the Syntor X is fairly simple, and involves the following basic steps:

  • Determine how to get the needed signals from the TNC into the radio. This boils down to deciding which functionality of the standard radio you don't need, and therefore which control cable wires you can steal.
  • Attach some type of connector to the control head and/or the control head end of the control cable which allows you to connect the TNC to the selected wires. You can also wire a switch to change between voice and data modes if you wish to be able to do so.
  • Make any needed changes to the radio end of the control cable.
  • Make the needed changes to the radio. There are a few jumpers to remove, and a few wire or diode connections to add.

I personally prefer to make the least invasive modifications possible. If this work is done in a considered way, the radio, cable and head(s) remain usable in other setups. This principle drives a number of decisions to be made during the process.

Equipment used
  • Soldering iron and solder.
  • Basic hand tools.
  • Hookup wire.
  • Connector for attaching TNC.
  • Switch for changing radio between voice and data. Optional, but it seems a waste to make the radio/cable set useless for voice when it's trivial to do both.
  • Some kind of box in which to mount the above connector and switch. Optional, but you'll be happier if you do this neatly. I used a surface mount data and phone wiring box, and then installed an RJ-11 jack plugin as the connector which links the radio to the TNC.
  • The Motorola tool for extracting pins from the control cable connectors. The part number is 66-84690C02, and they cost a couple of bucks. You can probably either find a local radio shop that can get you one, or a buddy who already has one. It's also possible to order parts directly from Motorola via their 800 number, though there may be a minimum order.
Stealing wires

A basic packet system requires the following signals: transmit audio, receive audio, ground, and push-to-talk. Since the Syntor X has two audio inputs (voice and data), there's one more signal specific to these radios: transmit mode select.

The large connector on the front of the radio is referred to as J1. All the signals we need for packet are available there, as follows:

  • Pin 2 delivers discriminator audio
  • Pin 7 takes data transmit audio
  • Pin 4 takes PTT
  • Pin 10 (among others) is ground
  • Pin 36 takes tx-in-data-mode
Of these, pins 2, 4 and 10 reach the control head through the typical control cable, so are readily available for tapping. The typical control cable contains one spare wire, colored red and blue, which can be used with impunity, though it may have to be moved from one pin to another inside the radio-end connector. So, we're down to one signal which still needs a wire. We'll have to steal one. Unfortunately, of the things which are hooked up in the typical cable, none are completely extraneous, so we must now decide which function is least needed.

The following signals are available in the typical cable and could be stolen with some loss of functionality, but would still leave the radio usable:

  • PL/DPL Disable -- if you don't use PL or DPL in your area, or if the radio is exclusively for data use.
  • Display Enable -- if you don't care too much about channel selection or active channel indication during scan.
  • Squelch -- if the radio is used only for data, most TNCs can do carrier detect in software.
  • Mic Hi -- if you are using the radio only for data (injected through another wire).
  • Scan Enable -- if you don't need scan, or are using the radio only for data.
Some of these options are decidedly repugnant, but your situation may dictate unusual measures.

Lack of some of these signals in the cable (due to our theft) can be made up in other ways. For example, PL/DPL Disable could be done by converting the radio for twice as many modes, then programming the lower bank with PL/DPL, and the upper bank without. Scan Disable could be achieved in the same manner, if one also jumpers J1-31 to J1-8 inside the radio. Squelch could be jumpered inside the radio.

I personally prefer stealing the scan enable wire. I don't find scan all that useful in most situations, and am willing to do the 64 mode modification and bank programming trick if I find I need it.

Once you've selected the signal whose wire you will steal, you have enough wires to complete the project.

Cable modifications at the control head end

If you wish to do the 64-mode conversion, now may be the time. See the relevant page on Mike Blenderman's site for details. Clamshell heads have a factory supplied location for a switch, so that part of the install is straighforward, though some of the wiring requires a nearly complete disassembly of the control head. I've found that System 90*s heads without PRI (scan) buttons have enough space to the right of the Mode 8 button to glue a switch to the circuit board; a neatly drilled hole in the front of the box will allow this switch to protrude.

The packet-specific modifications can all be done to the cable, rather than involving the control head. The method is to "vampire" onto the wires. I do this by cutting the Motorola wire a few inches back from the connector, stripping both ends as well as the feed wire from the TNC, inserting all three ends into a small collar and soldering. The small collar can be the rear part of a crimp-type ring terminal, or you may be able to find purpose made collars. After the solder is set, I slide the shrink wrap down the wire to cover and shrink it.

The wires I vampired on all go into a small box; I use the modular wall-mount type used by network and telephone installers. An RJ-11 jack provides the connection point for the cable from the TNC. I can also drill other holes in the front of the box for mounting switches (e.g. the voice/data one). You can tie the box back to the cable if you want, or come up with other schemes. On the last one I did, I actually placed a molex connector between the Motorola cable and the modular box. This would let me stick the modular box to the control head and yet be able to disconnect all the cabling to take cable or head elsewhere. Finally, I always wire the RJ-11 setup the same way, which means I only need one cable per device to play with any combination of transceiver and TNC

Remove the Wht/Gry wire from the #1 spot on the purple connector. If your setup wasn't originally endowed with scan, then you may not have this in quite the same spot. I suggest putting a little shrink wrap around the pin and preserving it that way in case you ever want to undo the mod.

The following are the connections you need to make:

Signal Wire color Pushbutton head Clamshell head
Data RX Audio Blk/Brn Black-16
Data TX Audio Wht/Gry now N/C
PTT Blk/Org Black-22
Data/Voice switch Red/Vio N/C
Ground Blk/Vio Grey-2/13

Inside your modular box, connect the Ground lead to some kind of terminal, as you'll have several things which need to connect to it. Connect the Data/Voice lead to one side of the switch. Connect the other side of the switch to Ground. Connect the cathode of a 13.8 V Zener diode to the Data/Voice lead. Connect the other side of the Zener to ground. Connect the Transmit Audio, PTT and RX Audio leads to the connector which will lead to the TNC. Connect the Ground pin of the TNC connector to the ground point in your box.

ALERT: I've twice had the quad bilateral switch IC which selects the data audio path fail in one of my packet radios. I'm starting to suspect that a capacitor in series with the audio path would be a good idea. You may wish to consider this. Better information as I have it. (2008-06-03)

Here's the pinout I use for my RJ-11 connector:

Signal KB8ZQZ RJ-11 pin
Data Tx Audio 2
Data RX Audio 4
Ground 5

That's it at this end of the cable. Button your box up neatly and tie it to the cable.

Cable modifications at the radio end

The work at the radio end is simpler to describe. The objective is to move two pins from one point to another inside the large connector. Specifically, move the wire from J1-31 to J1-7, and move J1-34 to J1-36. Working inside the large connector is cramped, and you need to be careful not to squish the wires at the edges or around the big connector knob.

To get the connector open, peel up the corners of the gasket around the connector, one at a time. Remove the screw you find underneath. Remove the C-clip retainer ring from the big connector knob. (This will enthusiastically go whirring off into another dimension if you're not careful.) Remove the big knob. The back of the shell should now come off the cable and front parts.

To get a pin out of its socket, observe how the pin on the control head would mate with the pin in the cable. Orient your pin removal tool the same way, and slide it into the socket. If you now push quite firmly, taking care not to twist or bend the tool, you should be rewarded with a click, and the ability to pull the wire and pin out from the back side. If you can't get the click, remove the tool, turn it 180 degrees, and try again. Fun, isn't it?

Radio modifications

This is the easy part -- lots of room to work. I assume you have an HLN-4760 flavor personality board. If not, you'll have to adapt these instructions. Mike Blenderman's site has some nice diagrams for this part. For the jumper changes, you'll have to have both sides of the radio accessible. For the other work, you can do everything from the solder side of the personality board. Here are the steps:

  1. Remove JU2 to disable PL/DPL reverse burst. This will cut a couple hundred milliseconds off your turnaround time. These jumpers are usually 0-ohm resistors, with a single black line around the middle.
  2. Connect JU12 to enable the data tx audio path. This part is missing from Mike's instructions. Reuse the resistor you removed above, thereby making this ordering of the instructions clever.
  3. Remove JU8, thereby enabling the data audio line to control the IDC circuitry.
  4. Connect the IDC Enable line on J4 (if you lay the radio bottom side up, handle toward you, it's the right-hand pin) to pin 4 on J103 using a garden-variety diode. The cathode of the diode goes to the J103 end. J103 has pins 1-6, a gap, then pins 8-14. This ends up disabling mic audio during data-mode transmission
  5. Connect pins 10 and 8 of J103 with a short piece of wire. This arranges for PL/DPL to be disabled on data transmission.
  6. Connect pins 1 and 3 of J103 with a garden-variety diode, cathode towards pin 3. This re-enables reverse-burst in PL/DPL modes for voice transmissions.
  7. Connect pins 3 and 4 of J103 with a short piece of wire. This completes the hookup of the voice/data switch.
  8. Connect pins 8 and 31 of J1 with a piece of wire. This enables scan, if the programming calls for it.
You're done!

Now button it all up and go test to make sure data audio comes out only when the switch is set to data, voice in voice mode, that PL works appropriately, etc.

This page created by Dennis Boone, KB8ZQZ, jm-sxg at yagi dot h-net dot msu dot edu.