Extended Range Direct Mode

Extended Range Direct Mode enables repeater operation on a simplex radio channel. Radios on an ERDM channel transmit on one slot and receive on another slot - the frequency is the same.

With this you get:
  • Repeater-like coverage
  • No need for a 2nd frequency - your simplex channel can be reused.

In this configuration, dual slot operation is not possible and you need to be using a SLR series repeater. IP based dispatch solutions, like SmartPTT Plus and TRBONET Plus, are supported. It also only supports single site conventional operation so no trunking or IPSC.

This feature requires R2.7.0 firmware and is supported on all current generation MOTOTRBO radios. My understanding is that this feature will also work on other makes of DMR radios.

Postscript 20.01.17

Before deploying ERDM, you must check with your local authorities as a simplex frequency licence is tied to a smaller geographical area (i.e. no more than 5km from point X is allowed). Installing a repeater (even though it uses a single frequency) may violate your licensing conditions.

- Thanks and credit to Craig Matthews for pointing this out.

Postscript 04.03.17

A Circulator cannot be used as it does not offer sufficient isolation (<30dB).

- Thanks to Jim for trying this out. Even a negative result is a result. 

Postscript 30.05.18

The SLR1000 has an optional built-in high speed antenna switch that will allow the repeater to be used with a single antenna. The same could be said about the other repeaters but Motorola doesn't produce an antenna switch for them unfortunately.

The antenna relay cannot be used as this is an electro-mechanical device that cannot cope with the high speed switching.

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