[op25-dev] Control channel questions

Alex alex323@gmail.com [op25-dev] op25-dev at yahoogroups.com
Mon May 8 03:44:16 UTC 2017


Hello,

Let's say you're scanning the airwaves in the frequency range of a
known P25 system and come across a spike in power at one particular
band that never shuts off.

* You should think that you've located a control channel, correct?

* If so, is it safe to say that the upstream and downstream channels
  are side-by-side (one contiguous frequency band)?

* What is the most accurate way of determining whether what you've
  discovered is a Phase I or Phase II system?

* When someone keys up a radio, is the following sequence of events
  accurate?:
  1. The radio sends a packet via the upstream control channel
  indicating that it wishes to speak.
  2. The fixed site sends a packet via the downstream control channel
  indicating a frequency X on which it wants the speaker to transmit.
  3. The fixed site sends a packet via the downstream control channel
  instructing all radios in the talk group to tune in to a frequency Y.
  4. The speaker transmits on frequency X, and the fixed site acts as a
  repeater, re-broadcasting the audio to frequency Y.

-- 
Alex
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