This is a Work In Progress

The Tait TB7100 is an FM repeater. It's a relatively simple device made up of two TM8100 series radio boards, a “User Interface” board that allows the operator to change channel etc, and a “System Interface” board that does some some signal conditioning, basic logic, and fan control.

As you'd expect from Tait, a plethora of IO is broken out on a DB25 connector on the rear of the repeater.

A batch of Multitone pager transmitters have recently appeared on eBay. These are a TB7100 chassis with a single 50w VHF radio fitted on the transmit side, and an additional “paging interface board” to re-map some of the internal connections and condition the incoming AFSK paging signal before its transmitted.

As-is they're probably not much use to amateurs as paging is commonly on UHF and other applications will require access to the Rx audio, but it's relatively easy to either convert them back into a duplex repeater, or re-route the connections internally so we can access both the Tx and Rx audio on the single radio.

In my opinion this is worth the effort, as the chassis provides a nice 1U rack mount platform with power distribution and suitable cooling for high duty cycle operation, and room for some combination of a duplexer, AC power supply, NinoTNC, MMDVM, or Raspberry Pi.

• The speaker and volume control on the UI board are hard wired to the absent receive radio, so monitoring the transmit side isn't possible without modification
• Likewise any Rx audio outputs on the DB25 system connector are also hard wired to the absent receive radio, so won't output any audio without modification.
• The UI panel requires 13.8v and 3.3v, which is normally taken from the receive radio. In its absence, the paging interface board takes 13.8v from the auxiliary connector on the Tx radio, and drops it down to 3.3v. If the paging interface is removed, the UI panel will malfunction. Modifications are required to resolve this.
• The TB7100 programming software won't program a radio with “standard” firmware, and the TB7100 specific firmware doesn't appear to be publicly available. However, you can use the TM8100 software, and it doesn't appear any functionality is lost.
• Warning: If you power up the repeater whilst modifying it without completing all the steps, you may find it starts to transmit at 25w, drawing over 4 amps. Make sure you're using a suitable power supply and a dummy load (The radio should reduce the output power if it detects high SWR, but best to avoid risking it)

To convert the pager transmitter into a duplex repeater, you will need to transplant in an Rx radio, 3x ribbon cables, a DC power lead, and appropriate coax / connectors / duplexer (optional)

If you're planning to use the TB7100 for simplex use (Packet node, analogue gateway, etc) you'll probably want to remove the Multitone Pager Interface to free up some room in the enclosure. Unfortunately it's not quite as simple as just removing it, as without it the UI interface will malfunction. This is because in normal operation it takes 13.8v and 3.3v from the Rx radio, which is absent. As a workaround, the pager interface takes 13.8v from the aux connector on the Tx radio, drops it down to 3.3v, and supplies both these voltages to the Rx connector on the UI board. It's also not possible to monitor the receive audio on the Tx radio, as this is hardwired to the Rx side.

To fix these issues, we can instead split the signals and voltages coming from the connector on the Tx radio control head connector, and shuffle them around so everything's in the correct place. This will also free up the aux connector on the Tx radio for interfacing with your TNC or other controller.

Note: This solution is slightly half baked. The connections to the system board will be removed, meaning it will only be providing DC distribution and fan control - There will be no I/O exposed on the system connector. If you need more space you could remove the system board entirely, or if you need the I/O you could perform some additional re-mapping internally, but as availability of these particular pager transmitters has dried up, we'll go with a quick solution for now.

tait_multitone_paging_interface_fitting.pdf

tait_multitone_pager_module.pdf