data slicer

[tulsascan]

hello friends
looking for a data slicer that will work on ltr,apco25,edacs,motorola types
that i can build my self. from what i have read ltr is diffrent than the 4 level or do i need to build two seprate slicer?

 

[mam1081]

As far as I know, you would need a 4-level for APCO, but since there really isn't software to decode it, it's really not useful. If you look under this forum: http://www.radioreference.com/modules.php?name=Forums&file=viewtopic&t=13427 you will find a schematic that should work for all the others you listed. Good luck!

 

[SCPD]

The 4 level won't work with P25. It's built for stair-stepped waveforms like 4 level FSK, not CQPSK.

P25 software - using a computer sound input - is on the way.

-rick

 

[poltergeisty]

Is'nt there two modes to p25? c4fm and qpsk. And is c4fm a stair stepped waveform? becuse to me I have understood that you would need a 4 level data slicer to decode p25. And would base band audio output work better for input of computer detection of this signal? Basicly what is the heart of a p25 signal is it like an internet protocal. Becuse you say a audio to the computer is going to be used which sounds like no data slicer will be needed. That be cool. But a little confused?

 

[SCPD]

And is c4fm a stair stepped waveform?

No ... C4FM is not the same as 4 level FSK. Both C4FM and CQPSK are shaped by a raised cosine filter - the difference being that the CQPSK signal is being shaped in both [carrier] phase and amplitude to further limit bandwidth needed while the C4FM signal is shaped only in phase.

If you look at both signals coming from a narrow FM discriminator, they look almost the same - the peaks on the C4FM signal will be taller than the CQPSK signal

-rick

 

[poltergeisty]

And is c4fm a stair stepped waveform?

No ... C4FM is not the same as 4 level FSK. Both C4FM and CQPSK are shaped by a raised cosine filter - the difference being that the CQPSK signal is being shaped in both [carrier] phase and amplitude to further limit bandwidth needed while the C4FM signal is shaped only in phase.

If you look at both signals coming from a narrow FM discriminator, they look almost the same - the peaks on the C4FM signal will be taller than the CQPSK signal

-rick

Do you think becuse of the complexities used for cqpsk that signal integrity would be harder to come by compared to c4fm? I would think that this would be an issuse in areas where you would only get 1 bar of signal for example and decoding is not 100 percent where is a c4fm signal at 1 bar dose come in.

 

[SCPD]

Do you think becuse of the complexities used for cqpsk that signal integrity would be harder to come by compared to c4fm? I would think that this would be an issuse in areas where you would only get 1 bar of signal for example and decoding is not 100 percent where is a c4fm signal at 1 bar dose come in.

Think of it this way ...

A hand-held radio can put out 5 watts into a signal spread out over 12.5 khz or it can put the same energy into a 6.25 khz spread.

An FM discriminator will see the 6.25 khz signal as weaker because it only measures phase or deviation from a center frequency. A properly designed receiver built for CQPSK - an in-phase/quadrature phase design for example - would be able to capture phase and amplitude information.

So ... if you're using a FM discriminator to capture a CQPSK signal then yes you will be sacrificing range or signal quality for simplicity.

-rick

 

[dynamitedjs]

I have a 4 level for sale if anyone is interested. $40.00 plus shipping to your zip code ups. It's already assembled and needs a 12 volt power supply.

 

[poltergeisty]

Do you think becuse of the complexities used for cqpsk that signal integrity would be harder to come by compared to c4fm? I would think that this would be an issuse in areas where you would only get 1 bar of signal for example and decoding is not 100 percent where is a c4fm signal at 1 bar dose come in.

Think of it this way ...

A hand-held radio can put out 5 watts into a signal spread out over 12.5 khz or it can put the same energy into a 6.25 khz spread.

An FM discriminator will see the 6.25 khz signal as weaker because it only measures phase or deviation from a center frequency. A properly designed receiver built for CQPSK - an in-phase/quadrature phase design for example - would be able to capture phase and amplitude information.

So ... if you're using a FM discriminator to capture a CQPSK signal then yes you will be sacrificing range or signal quality for simplicity.

-rick

This makes sense. Thanks. I kinda of thought that would be the case. This must be why some times a qpsk signal is harder to hear with a scanner. They did not design the scanner right.

 

[dsnymj]

I can't wait for a trunker program for p25 9600 baud. I live in Colorado and it is all pretty much 9600 baud out here.

Check out Pro96Com (on the software downloads page under Trunked Radio Decoders). It decodes the 9600 CC data stream from a Pro-96.

 

[poltergeisty]

I can't wait for a trunker program for p25 9600 baud. I live in Colorado and it is all pretty much 9600 baud out here.

Check out Pro96Com (on the software downloads page under Trunked Radio Decoders). It decodes the 9600 CC data stream from a Pro-96.

Thanks, I don't currently have a pro 96 any more. Did not like it but if I don't see anything for the os 535 or 296d uniden then I will probley have to go buy it again just for that purpose. :wink: