• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:
    https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html

P25 True-False

Joined
Sep 4, 2017
Messages
36
#2
Should we go with CDMA or TDMA?

It's all the same as cellular phone technology.

Be sure to remember to put your SIM card in your radio.
 
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#3
I gather that at that time (copyright is 2014) Tait had no P25 solution that supported TDMA. Moot now since they seem to. The link below doesn't pooh-pooh TDMA the way the other one does.

Their marketing people, in addition to failing to keep outdated material off their site, don't seem to know math, either. They claim (in the new link!) that dividing a 12.5 kHz wide channel results in two 6.75 kHz channels.

Hey, but it's on the internet so it has to be true.

The Norman departments (not nearly all of them!) that are actually using new radios sound great. Amazing what can be done in 6.25 kHz (not 6.75 ...). Big difference in the audio coming from a new radio and the audio coming from an old radio ... that goes to the tower ... that goes to the controller in Tulsa via IP ... that comes back to the tower ... that goes out on RF ... to a bridge radio connected to the new systems. :LOL::LOL::LOL:


Tait Connection - Issue 8 - page0
 

GTR8000

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#4
Except that P25 Phase II doesn't use 6.25 kHz wide channels. ;)

Phase II utilizes the same 12.5 kHz wide channels that Phase I does, except that it divides that same channel up into two alternating slots of 30 msec each, hence the T in TDMA (Time-Division Multiple Access).

TDMA results in 6.25 kHz spectral efficiency, meaning that since you wind up with two distinct voice paths within a single 12.5 kHz channel using those two aforementioned alternating time slots, then you have effectively created the equivalent of two separate 6.25 kHz wide channels.
 
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#5
Except that P25 Phase II doesn't use 6.25 kHz wide channels. ;)

Phase II utilizes the same 12.5 kHz wide channels that Phase I does, except that it divides that same channel up into two alternating slots of 30 msec each, hence the T in TDMA (Time-Division Multiple Access).

TDMA results in 6.25 kHz spectral efficiency, meaning that since you wind up with two distinct voice paths within a single 12.5 kHz channel using those two aforementioned alternating time slots, then you have effectively created the equivalent of two separate 6.25 kHz wide channels.
I always forget that - it's essentially half of a 12.5 kHz channel but cut width-wise and not length-wise! :p

Regardless, it's not 6.75 kHz either and it really does sound fine.
 
Joined
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Messages
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#6
I always forget that - it's essentially half of a 12.5 kHz channel but cut width-wise and not length-wise! :p

Regardless, it's not 6.75 kHz either and it really does sound fine.
Was just watching something today about the IMAX theater. They were turning the film 90 degrees and feeding it that way instead of the traditional way. They're able to get more picture turning frames the other way. They were also able to get 3D. And the camera was like 300 pounds or something like that. With digital they're able to cut down the bandwidth and still with compression/vocoder get the signal through.

I gather that at that time (copyright is 2014) Tait had no P25 solution that supported TDMA. Moot now since they seem to. The link below doesn't pooh-pooh TDMA the way the other one does.

Their marketing people, in addition to failing to keep outdated material off their site, don't seem to know math, either. They claim (in the new link!) that dividing a 12.5 kHz wide channel results in two 6.75 kHz channels.

Hey, but it's on the internet so it has to be true.

The Norman departments (not nearly all of them!) that are actually using new radios sound great. Amazing what can be done in 6.25 kHz (not 6.75 ...). Big difference in the audio coming from a new radio and the audio coming from an old radio ... that goes to the tower ... that goes to the controller in Tulsa via IP ... that comes back to the tower ... that goes out on RF ... to a bridge radio connected to the new systems. :LOL::LOL::LOL:


Tait Connection - Issue 8 - page0
Like what's with travelling clear around the world and coming back just to send me a message? What's that all about? What if the IP link breaks down? Does it fail RF on a local tower because the IP link in some other town beyond the line of sight of RF is not available to participate as the main controller? What's it doing? Recording all conversations in a data center somewhere else?

The rule is this: KISS!
 
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