Feds pushing Project 25

[N_Jay]

. . or better yet, some GMRS swith to Apco or Apco 25. . . .

I do not think P25 is allowed on GMRS.

 

[N4DES]

That is correct...it is not allowed.

 

[WayneH]

The math is simple calculus. None of the documents say that digital has better range. The documents just lay out the procedures for evaluating systems - I did not see any comparisons that had been actually conducted.

Peter, I don't think you're going to get a cut and dry answer that will convince you. I know for a fact it gives you greater usable range based on experience with the technology. You get a better representation that way versus pulling out a calculator and getting an unrealistic answer.

 

[zerg901]

Wayne H - thanks for your reply.

Could I ask 1 more question?

How much better is the range of digital over analog?

I think the answer is 5% - but that is just a wild guess. (I am sure that if P25 had 25% better range than analog, that I would be seeing that 25% number all over the Internet.)

Peter Sz

I know that N Jay gave some guess in dB, but that is greek to me.

 

[WayneH]

Wayne H - thanks for your reply.

Could I ask 1 more question?

How much better is the range of digital over analog?

I'm really not sure how to apply a number to it. There are going to be times where the usable range is comparable and in some instances the recovered audio will be more intelligible on the fringes where all you would get is static over audio with bits of words here and there.

The fringe areas are really where you gain any benefits.

Outside of range P25 has some nice background features. It's nice not having MDC chatter.

 

[N_Jay]

. . . .
I know that N Jay gave some guess in dB, but that is greek to me.

That is like asking how hot is boiling water but you don't understand the concept of "Temperature".:roll: :roll:

 

[richardc63]

The math is simple calculus. None of the documents say that digital has better range. The documents just lay out the procedures for evaluating systems - I did not see any comparisons that had been actually conducted.

I am not trying to take any shortcuts.

I will ask again - does anyone (besides N Jay) have a URL leading to a official document that says digital has better range than analog?

I checked the FCC website. I found nothing that said digital has better range. In fact the descriptive / explanatory material on the FCC website doesn't even seem to mention P25.

Peter Sz

Peter,

I think you are asking a question for which there is no black & white answer. There are too many factors which impact on propagation which can't be predicted in a real field situation. Things such as multipath for example (dense timber etc). Anyone can do a bench test & give you an answer. That was the first test I did when I got my new Aeroflex-I found the point at which the digital signal "R2D2ed" was 1dB less than the signal level at which the analogue signal became unuseable. That was using about 5 different XTS5000s. That is not an answer to your question- just an indication that there is no reason why it should be significantly different.

I can also tell you I did a real test prior to the recent APEC in Sydney. Using the government's dual mode ASTRO/Smartzone system I found there were locations that I could get out with no detectable noise/distortion using ASTRO whereas the analogue was unuseable. Both base equipment was using a common aerial. The results blew a few people away (including me) and was explained by Moto as "the benefits of having forward error correction". I was using my XTS5000 during these tests.

I believe that is the most practical answer I can give you without you defining the conditions under which you asking for the comparison to be made.

Cheers,



Richard

 

[zerg901]

We could compare digital vs analog in a "theoretical" place - flat land - no vegetation. North Pole, South Pole, Western Australia, Sahara, North Dakota -), etc.

This discussion has resurrected an old question for me. If a digital system is operating as a "synchronized simulcast" system, is wideband operation required? (20 kilohertz wide channels).

Motorola had a tutorial online about 5 years ago that talked about wide ASTRO vs narrow Astro. I think I lost that tutorial. Anyone have it?

Peter Sz

 

[N_Jay]

We could compare digital vs analog in a "theoretical" place - flat land - no vegetation. North Pole, South Pole, Western Australia, Sahara, North Dakota -), etc.

This discussion has resurrected an old question for me. If a digital system is operating as a "synchronized simulcast" system, is wideband operation required? (20 kilohertz wide channels).

Motorola had a tutorial online about 5 years ago that talked about wide ASTRO vs narrow Astro. I think I lost that tutorial. Anyone have it?

Peter Sz

Yes, No, Maybe!

It is all about modulation type and site separation (and again, there are not hard rules, but it requires in-depth calculations).

Motorola wide-pulse 20 KHz is no longer offered (I believe)
CPQSK simulcast modes that allow decent separation (about 7 to 15 miles).
Regular C4FM is about 1/2 that I have been told.

 

[zerg901]

<http://www.p25.com/resources/P25TrainingGuide.pdf>

P25 uses 12.5 kHz channels - but there is scant mention in this document about simulcast systems - so maybe 20 kHz channels ARE (WERE) used, but not unless synchronized simulcast is required

Digital coverage vs analog coverage - several paragraphs address the issue but they dont come to a firm conclusion - in fact, it sounds like digital simulcast might experience some dead spots that are TOTALLY dead - kinda a 'good news, bad news' thing - you have better coverage in most areas, but some areas might be TOTALLY dead

 

[kb9sxk]

Yep, did you notice that according to this reporter the Gregg Co. SO uses HF to communicate! :roll:

27.185???????????