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Tait Cross-Band Repeater Build
For an event, I (Tom M0LTE) needed to provide a cross-band FM repeater.
A cross-band repeater is a system which receives signal on one band and re-transmits it on one or more others. This is reversible, i.e. the signal can be received on either band and transmitted by the other radio.
This allows stations which are not line-of-sight with each other to be able to communicate directly.
In my case, I needed a system that would bridge between 2m and 70cm, which is probably the most common combination.
I do have a Wouxun KG-UV950PL, which can do this out of the box, but my gut feel is that is meant for occasional use, since the thermal management of that radio isn't great and cross-band repeat generally means you end up transmitting at a much higher duty cycle than if you were just using a radio as normal.
So I decided to re-purpose some of my commercial radios I have around for the various packet radio projects I do. I chose a Tait TM8100 as the 2m radio and a Tait TM8200 as the 70cm radio.
These radios are explicitly designed to support cross-band repeat, and there are supporting notes in the PDF entitled “MMA-00041-04 - TM8260 Installation and Programming Guide”, available online.
I didn't find a full write-up of how to do this, and the manual over-complicates it a bit and spreads the information around, so I thought I'd write it up.
Cable
The Tait manual references a particular off-the-shelf cable, which I don't have, but you can build one easily:
Using the rear D sub 15 pin connector:
| Pin, radio 1 | Pin, radio 2 | Role |
|---|---|---|
| 2 (busy) | 12 (ptt) | when radio 1 receives a signal, assert ptt on radio 2 |
| 7 (tx audio) | 13 (rx audio) | Send audio received by radio 2 to radio 1 for transmission |
| 12 (ptt) | 2 (busy) | when radio 2 receives a signal, assert ptt on radio 1 |
| 13 (rx audio) | 7 (tx audio) | Send audio received by radio 1 to radio 2 for transmission |
| 15 (gnd) | 15 (gnd) | Provide a return path for the signals above |
The D sub 15 pin connector is numbered like this, looking at the back of the radio (and therefore also looking at the solder side of a plug):
8 -------- 1 15 --- 9
Settings
On both radios, you need to set the following configuration:
Programmable I/O form, Digital tab
| Pin | Direction | Label | Action | Active | Debounce |
|---|---|---|---|---|---|
| AUX_GPI1 | Input | XBAND_TX | Crossband TX Input or EPTT1 | Low | 10 |
| AUX_GPIO5 | Output | Busy | Busy Status (no CTCSS) or Signalling Audio Mute Status (CTCSS) | Low | None |