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ASTRO Digital modulation

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station32

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I have looked this up and read a little but i still dont really get the difference. C4FM is p-25 digital if i am not mistaken. What is CQPSK and WIDE i saw them in the cps unter conventional and astro can any one help me out?
Thanks in advance
 

n3obl

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CQPSK is for use on simulcast trunked systems. Not sure was WIDE is for.
 

N4DES

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Wide should be used in simulcast. CQPSK is for other special applications that use 6.25 kHz of bandwidth.
 

MattSR

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Kind of - Theres two flavours of simulcast, the old WIDE which isn't P25 compliant and uses a 25kHz channel, and the newer LSM (CQPSK based) Linear Simulcast Modulation which uses a 12.5kHz channel and is defined in the P25 standards.

WIDE is old, spectrally inefficient and not P25 compliant.

LSM is the new P25 compliant CQPSK based Simulcast thats popping up everywhere.

Max, KA1RBI has done an analysis and written a GNUradio decoder for this. Lots of juicy LSM info here - LSM Gallery
 

rbrtklamp2

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Ive wondered about this for a while too I would love to see the definition of how the different modes are used and what purposes they serve? The CPS isn't exactly forthcoming when it comes to defining these three modes.

Thanks for any answers,
Bob
 

Rescue1

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I agree. What would be really cool is if someone were too take the time(a lot of time) and explain all the crazy menus upon menus in CPS. Sort of like the guides on how to disassemble the ASTRO radios, and the one about the workings of the radios, and encryption. Those are simply awesome, and those authors are amazing for doing the work...:)
 

Scanner-geek

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Is it possible that an APCO25 transmission can sound "encrypted" when in actuality it is not encrypted, because of a prgramming error? I have been trying to monitor a conventional APCO25 channel with an XTS5000, but SOME of the transmissions are garbled, suggesting encryption, while others are in the clear.
A local commercial radio enthusiast assures me that this particular channel is NOT encrypted, and that he is able to regularly receive ALL transmissions on this frequency in the clear using a Motorola radio. His assertion is that it is a programming error on my part.

I have the CPS and have been playing with the settings but can't seem to receive it entirely in the clear. Has anyone else come across this phenomenon? Is there a parameter in the CPS relating to Astro that I am missing? Or am I to assume that this knowledegable individual is incorrect and the channel is in fact encrypted on selected transmissions. A third party inferrred that my problem was with P25 "encoding" and NOT "encryption" and that this frequency was monitorable in the clear with the right equipment. He did not elaborate. I assume an XTS5000 and CPS are the right equipment for Astro P25 conventional transmissions.

Is there anyway I can differentiate an "encoding" issue from encryption? Also, why would only certain transmissions be encdoded or encrypted? How can I confirm that this channel is, in fact, encrypted?

I would greatly appreciate any insight into this
 
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