Extended Range Direct Mode

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Extended Range Direct Mode (ERDM) is a radio and repeater feature that allows repeater operation on simplex. Rather than requiring two frequencies, a user is able to achieve repeater-like coverage using a single frequency. For many users this means that they do not need to obtain a more costly repeater frequency allocation and can gain most of the benefits of repeater operation while using their existing simplex frequency allocation.


A radio initiates a transmission as it does in direct mode and can receive transmissions directly from a radio or from the repeater. At the beginning of reception, the radio selects the signal based on the operational mode. Therefore direct mode operation is still supported in the absence of the repeater without the radio user having to change channels.

ERDM is supported in all SLR repeaters. In order to use a single antenna for transmit and receive, a high speed antenna switch is needed. The (electromechanical) antenna relay, available as an option or accessory on older repeaters, cannot be used for this. There is a high speed switch available for the SLR1000 that uses PIN diodes. This switch cannot be used with higher RF power which means that a 3rd party switch is needed when this is used on the SLR5500 and SLR8000.

Compatibility Mode

Extended Range Direct Mode with Compatibility Mode enabled supports older MOTOTRBO Radios and mixed radio fleets. Using Extended Range Direct Mode without Compatibility Mode means older radios and other makes of radios are not supported but the following features can be used.