• 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.

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Determining P25 C4FM and CQPSK Control Channels

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EricCottrell

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Hello,

I decided to post to a new thread since this message is about methods and not results. I am planning on doing some testing as I have a HP-1, 396XT, PSR-800, and soon a 536HP. I have several P25 simulcast sites in my area. How can I tell? The signal waveforms from a FM discriminator are different.

The scope function of Unitrunker can be used to determine the type of modulation used by the control channel. I used the HP-1 as an inline signal source with the filter off. The C4FM signal was from a non-simulcast 800 MHz system and the CQPSK signal was from a simulcast 800 MHz system. The CQPSK signal has narrower more defined transitions.

A scanner with a discriminator tap can also be used.

73 Eric
 

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AZScanner

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The systems used in my area definitely have the latter waveform example shown in your post (CQPSK), but honestly I could have told you that simply from how lousy just about every digital scanner in existence has ever peformed on them. However, I'm hearing good things so far from 536 owners as they start to chime in. I can't wait for my 436 to arrive.

-AZ
 

EricCottrell

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Hello,

Thanks. I know some scanner users have a good idea of the problem systems in their area. Others seemed to be commenting back that they are only interested in how the new Uniden scanners perform on known LSM systems.

73 Eric
 
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