Dual Capacity Direct Mode is a feature available in all second generation MOTOTRBO radios which allows two slot operation on simplex. Not only does it offer two slot operation but is also currently the only product which complies with ETSI TS102-361 §1-4 v2.1.1 for 6.25e operation on simplex.
DCDM - also known as 6.25 kHz Equivalence Direct Mode (6.25e DM) - provides additional spectral efficiency by supporting up to two simultaneous Direct Radio-to-Radio Mode subscriber calls within a 12,5kHz allocation of spectrum.

The CPS DCDM settings in a simplex channel

Price sensitive customers, migrating from Analogue to Digital (TDMA) can move up to two talk paths, with  6.25e Direct Mode (TDMA), without a repeater. It also increases the total number of users supported on a 12.5 kHz channel with no degradation in performance.
In DCDM radios automatically and cooperatively select a Channel Timing Leader for the RF Channel (regardless of slot). So that all radios receive the Direct Mode Channel Timing signalling communication, this signalling is communicated using the “All Site” Color Code (15).
In the CPS, there is one major setting relating to DCDM: the Timing Leader Preference. There are three choices: Preferred; Eligible and Ineligible. A likely candidate for Preferred would be a base station because it doesn’t leave the channel; is connected to the mains (or a large battery) and has better coverage on simplex.
One of the subscribers with the higher leader preference setting (usually Preferred) is elected as the Channel Timing Leader and if that leader leaves the channel, the system selects a new leader. The Channel Timing Leader periodically announces the Channel Timeslot Structure using special Beacons (600ms transmission every 4,5 minutes). If the timing is accepted, it is then re-transmitted using “Forced Propagations” to the next lot of radios further away from the leader.


  1. Hi Wayne,

    We wish to have 8 handheld only Mototurbo setup for covering area of ~1 aq km. I have a few questions regarding the same. Hope you don't mind.

    If I have two groups - Engineering (6 radios) and Maintenance (2 radios) programmed fot slots 1 & 2 respectively on a single 12.5 kHz frequency:

    1. Can we have groups where members from both slots could be present?

    2. Can a private call be established between members who are on different slots ?

    3. If two engineering radios are occupying slot 1 for a call, will call from 3rd engineering radio to a 4th switch to slot 2 automatically ? can it be done manually?

    4. Can text messages be sent to a user on different slot?

    5. Can talk permit tones be used in this scenario ?

    I appreciate you taking time to respond to these queries.

    Thanks & Regards

    1. My answers to your questions:

      1. Yes, if you use scan.
      2. Yes, but only if the target radio is not monitoring another call and only if scan is used.
      3. No, that would need to be done manually.
      4. Yes, but only if the target radio is not monitoring another call and all radios use scan.
      5. Yes, the radio will sound talk permit tones.

      NB: I am assuming that no repeater is used here!

  2. This comment has been removed by the author.

  3. Thanks Wayne for quick response. We are not considering any repeater here at least not now.

    What could be the impact of two slot scan Vs two frequency scan on batteries ? Same/lower ?


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