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P25 Information

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mous

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Hi guys,

I am new with the P25 technology and I have few questions, so I would appreciate your help.

I know that its is a C4FM modulation (FDMA) simulcast and I already know that 3 motorola GTRs are used in the design, on for Control, one is standby and the third is in TX/RX mode; So I want to know how many frequencies can the GTR TX/RX handle and how many voice channels can we have at the same time.
 

WayneH

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The GTR is a single channel trunked station. With Phase 2 a single frequency will be able to do two simultaneous transmissions.

I don't recall how many total channel resources a 9600 (ver 7.x) trunked controller can have. Maybe someone else can chime in.
 

greenthumb

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For single site there can be a maximum of 28 channels in FDMA and as I recall a maximum of 30 talk paths in phase II using a phase I control channel.
 

JRayfield

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P25 Phase 1 provides one voice channel per frequency. For a trunking site, at least two frequencies must be used - one for the control channel, and one for a voice channel. It sounds like you've got one extra repeater at the site for backup, but if it's not on-the-air as part of the system, then you only have one voice channel available, as you've described the site.

John Rayfield, Jr.
 

mous

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Thank you guys,

So it depends on the GTR capacity (TX/RX) and how many frequencies I'm able to assign.
One more questions, I am comming from a GSM Operator so i am trying to make some comparisions.
Can I assign more than one frequency for the GTR used for control, so One will be used as a control channel and the others for TX/RX ?? as in the BCCH and TCH in GSM ?
 

KA1RBI

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For a trunking site, at least two frequencies must be used - one for the control channel, and one for a voice channel.
I believe the specs make provisions for shared-use channels (channels which continuously broadcast OSP's, as do trunk CC's, but also can switch to voice mode when desired). Whether any vendor does this today is a different question.

Also, in a repeatered trunked system, with one dedicated channel for control and one for voice, a total of four frequencies would be used.

Max
 
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