Interfacing two-way radios with a Tecpro communication system

The Tecpro AD913 provides a plug and play method of joining one or more two-way radios to an existing comms system. The adaptor connects to the ring (and can loop out again) via 3-pin XLR. A radio transceiver connects via 6-pin XLR.

Radio users will only hear audio from the ring whilst a signal lamp is depressed (and will then hear all audio on the ring). This is intended, as otherwise a radio user would not ordinarily be able to send audio onto the ring.

The AD913 is not the only option when interfacing a radio system. If signal lamp-switching audio will not work for you, the Tecpro AD903 could be used instead, as described later in this article.

Kenwood’s K1 connector is used on a wide variety of radios. Many popular Chinese models, such as the Baofeng UV-5R and Tytera TYT-MD380 use this connector for accessories.

It’s worth noting that not all radios use the same pinout for the K1. Indeed, the AD913 data sheet example shows a different pinout for this connector. Check what your radio is expecting before making up your adaptor.

Pins 5 and 6 connect pins 1 and 3 when the signal lamp is depressed, triggering push-to-talk on the radio transceiver and completing the outgoing (to radio) audio circuit.

Continuous audio #

The AD913 only sends ring audio to the radio system while the signal lamp is depressed. This is intentional, allowing a single radio, acting as both transmitter (from ring) and receiver (to ring), to be used. It also allows for a simplex radio channel to be used, as a duplex channel would be required for continuous audio to be sent to radios from the ring.

If this doesn’t fit your requirements, the Tecpro AD903 2 to 4 wire adapter allows full two-way communication simultaneously. This will require either two radios at the interface unit – one to send audio from the ring to radio users and one to send radio user audio onto the ring – or a radio base station capable of full duplex transmissions.

This uses a 4-pin XLR connector running to two K1 connectors as follows.

Early builds and the documentation confusingly use ‘input’ to mean audio going from the ring to the 4-wire system and ‘output’ audio going from the 4-wire system onto the ring. Later builds clarified this with clearer labelling. Controls on the left are always for audio going from the ring to the 4-wire system and the right for audio going onto the ring from the 4-wire system. Similarly, documentation uses ‘hi’ and ‘lo[w]’ to refer to ‘line’ and ‘mic’ level respectively.