Digital Trunking scanners

[duke_nemmerle]

I've had a look at the wiki but I'm really in the dark about the diference between -digital- trunking and -plain ol'- trunking. Would someone care to venture to explain why I should spend 500 dollars on a digital trunking scanner? Or rather, since all of my local trunks are mundane -plain ol'- trunking systems, describe a scenario in which the extra money would be worth it.

Thanks

 

[ka3jjz]

If there were no digital trunks in your area, I certainly wouldn't recommend getting a digital tracker. However, that decision must be researched completly before making such a decision. Not only would I post questions about this in your state's forum here on RR, but I'd check the various Yahoo groups as well.

Of course, if you have an 'in' with the radio techs for your area, they sometimes have info no one else has

The only other item to consider would be channel capacity. Could you actually use, say for example, a 785 which has a 1000 channel capacity, sans the digital card? Or would a 780, with its 500 channel capacity, be enough for your needs?

I'd do my research, and make the decision based on your wants and needs. Sometimes it's as much a personal decision as it is a technical one.

73s Mike

 

[duke_nemmerle]

Yeah, I can't imagine it being worth it for me. Channel constraints are easily solved with computer control, which I use for everything except mobile and side listening, and I'm nearly sure that even the planned trunking system for my state police isn't going to be digital, though I'll have to recheck.

 

[911_Radioman]

The difference

With MOT stuff, the analog trunking uses a 3600 baud control channel signal. This, by the way, is maximum for Smartnet I, II and II+. There's no way a 'Smartnet' system of any flavor will ever be P25-compliant.

The digital systems that are P25 compliant now use a 9600 baud control channel signal exclusively. Earlier MOT variations (version 5.x) also used a 3600 baud signal. Their proprietary VSELP vocoder digital systems also used 3600 baud.

The new digital P25 compliant systems are also 12.5 kHz channels. Earlier analog trunking was 25 kHz. Later, there were 12.5 kHz analog trunked systems - these came out just before APCO 25 standards were established.

 

[BoxAlarm187]

Duke, what area are you in?

 

[911_Radioman]

Area 51

Jupiter.

Used to live in Coral Springs.

Working now in DC, and raising 8 kinds of hell!

 

[loumaag]

Re: The difference

With MOT stuff, the analog trunking uses a 3600 baud control channel signal. This, by the way, is maximum for Smartnet I, II and II+. There's no way a 'Smartnet' system of any flavor will ever be P25-compliant.

While this is true, you are forgetting there are many-many Motorola Smartnet/Smartzone systems using P-25 CAI modulation, which of course requires a digital scanner to monitor.

Another point to bring up is that there are lots of P-25 conventional systems out there where trunking is not a factor. Most federal governement conventional is P-25 (and may be encrypted also.)

 

[911_Radioman]

Incorrect

Smartzone - yes. Smartnet - no.

The digital modulation used on some Smartnet systems uses Motorola's proprietary VSELP vocoder - not the APCO 25 approved 'IMBE' vocoder - that IS the common air interface.

Also, APCO 25 calls for a 9600 baud control channel and other methods of accessing a trunked system. Smartnet is limited to 3600 baud on the control channel.

 

[loumaag]

Re: Incorrect

Smartzone - yes. Smartnet - no.

The digital modulation used on some Smartnet systems uses Motorola's proprietary VSELP vocoder - not the APCO 25 approved 'IMBE' vocoder - that IS the common air interface.

Would you like to reconsider this pair of statements? If not, then please provide a link to any reliable source that will back these up. While you are looking for that, look up Smartnet ver 4.1. :roll:

Also, APCO 25 calls for a 9600 baud control channel and other methods of accessing a trunked system. Smartnet is limited to 3600 baud on the control channel.

No, APCO-25 standard for trunking systems calls for a 9.6 KBS protocol, which since it is 4 level is actually 4800 baud. You are correct that Smartnet systems use a 3600 baud control channel; however, so do all Smartzone systems.

The point I was making was that there are Motorola trunking systems out there using P-25 CAI modulation. This is not to say they are full APCO-25 compliant systems (because if they were, I wouldn't be calling them Motorola); but from a scanner standpoint, you still need a digital scanner to monitor those systems. 8)

 

[911_Radioman]

Lou,

You're picking nits. :roll:

At Motorola, digital modulation is either produced with their own vocoder (still 80% of the digital product they sell) which is VSELP (Vector Sum Excited Linear Prediction).

The other kind (which they prefer not to sell) is IMBE (Improved Multi-Band Excitation). This is the vocoder that's TIA compliant for Project 25. It's an open standard that anyone can build.

The control channel on P25 systems is 9600 baud. Yes, voice modulation is a 4-level modulation (C4FM), but for the inbound signal packet, it is truly 9600 baud.

Look both these facts up in the TSB-102s, put out by the TIA. Sorry, it isn't a 'free download'. You have to pay for them.

Yes, when you get a voice channel on a P25 system, the digits are slower than 9600 baud. I recall having this discussion with someone at IWCE 2 weeks ago.

But if you'll re-read my statements, you'll see I was talking about control channel stuff - what an actual radio has to do to get a voice channel on the system - NOT VOICE CHANNEL MODULATION!

When an actual radio affiliates with the system, a whole lot more is going on than what happens in your 'toy' receiver from Radio Shack.

And no, I don't feel the need to reconsider anything I've said. :!:

 

[DonS]

The control channel on P25 systems is 9600 baud. Yes, voice modulation is a 4-level modulation (C4FM), but for the inbound signal packet, it is truly 9600 baud.

Why would we care about the "inbound signal packet"?
(EDIT: asking from a scanner user's point of view, given the title of this thread.)

 

[N_Jay]

At Motorola, digital modulation is either produced with their own vocoder (still 80% of the digital product they sell) which is VSELP (Vector Sum Excited Linear Prediction).

The other kind (which they prefer not to sell) is IMBE (Improved Multi-Band Excitation). This is the vocoder that's TIA compliant for Project 25. It's an open standard that anyone can build.

Where do you get this from?

If they "prefer not to sell P25 then whey are they discontinuing most everything else?

I think all indications are Motorola PREFERRES strongly to sell P25 systems.

The control channel on P25 systems is 9600 baud. Yes, voice modulation is a 4-level modulation (C4FM), but for the inbound signal packet, it is truly 9600 baud.

Look both these facts up in the TSB-102s, put out by the TIA. Sorry, it isn't a 'free download'. You have to pay for them.

I am fairly sure that the P25 control channel modulation is the same as the P25 voice channel modulation. (Why would it be different).

I don't have the TIA specs handy now, but I have checked several other sources.

I am very confident that the CAI, COMMON Air Interface (Note the word common) covers Voice, Data, Trucking control, and secure channels.
All with 9600 BPS C4FM/CQPSK 4 level (4800 Baud) modulation.

And no, I don't feel the need to reconsider anything I've said. :!:

You sure? :wink: :wink:

 

[DonS]

The control channel on P25 systems is 9600 baud. Yes, voice modulation is a 4-level modulation (C4FM), but for the inbound signal packet, it is truly 9600 baud.

Look both these facts up in the TSB-102s, put out by the TIA. Sorry, it isn't a 'free download'. You have to pay for them.

I am fairly sure that the P25 control channel modulation is the same as the P25 voice channel modulation. (Why would it be different).

I don't have the TIA specs handy now, but I have checked several other sources.

I am very confident that the CAI, COMMON Air Interface (Note the word common) covers Voice, Data, Trucking control, and secure channels.
All with 9600 BPS C4FM/CQPSK 4 level (4800 Baud) modulation.

That seems to be correct.

From TIA/EIA 102.AABB, section 1.3 (References):
1. ANSI/TIA/EIA 102.BAAA, Project 25 FDMA Common Air Interface, May 1998 - This document describes the basic over the air formats used on the Trunking control channel.

From TIA/EIA 102.BAAA, section 9 (Modulation):
9.2 Symbols
The modulation sends 4800 symbols/sec with each symbol conveying 2 bits of information.

 

[N_Jay]

The control channel on P25 systems is 9600 baud. Yes, voice modulation is a 4-level modulation (C4FM), but for the inbound signal packet, it is truly 9600 baud.

Look both these facts up in the TSB-102s, put out by the TIA. Sorry, it isn't a 'free download'. You have to pay for them.

I am fairly sure that the P25 control channel modulation is the same as the P25 voice channel modulation. (Why would it be different).

I don't have the TIA specs handy now, but I have checked several other sources.

I am very confident that the CAI, COMMON Air Interface (Note the word common) covers Voice, Data, Trucking control, and secure channels.
All with 9600 BPS C4FM/CQPSK 4 level (4800 Baud) modulation.

That seems to be correct.

From TIA/EIA 102.AABB, section 1.3 (References):
1. ANSI/TIA/EIA 102.BAAA, Project 25 FDMA Common Air Interface, May 1998 - This document describes the basic over the air formats used on the Trunking control channel.

From TIA/EIA 102.BAAA, section 9 (Modulation):
9.2 Symbols
The modulation sends 4800 symbols/sec with each symbol conveying 2 bits of information.

I typed "sure", then added the "fairly" since I did not have the document to quote. :twisted: :wink:

Maybe sciottos will be in the mood to reconsider? :roll:

Thanks for the confirm!

 

[loumaag]

TO: DonS and N_Jay,
Thanks for the replies, you saved me having to find the answers.

TO: sciottos
Umm, I may be wrong here, but Idon't think that Motorola has sold a Astro (VSLEP) system in a while. 80%, hmmm where did this come from? I am still waiting for you to post any reliable information or links to back up any of assertions.

I doubted you knew what you were talking about when you made your Smartnet/Smartzone comment earlier, you have just proven my earlier assumption.