Digital Trunking Talkgroups for fireground operations

[Wes]

I have noticed a couple of threads on the board and have seen some comments in reference to the NFPA 1221 standard on communications.....

I obtained a copy of the must current version (2002) and checked it out. I totally agree with what it says which is basically "Do not use trunking talkgroups for tactical on-scene operations." I was looking for where it states not to use digital. I couldnt find that exact wording. Anyone who has been part of a fireground operations and knows anything about radio systems would know that simplex analog is the ONLY way to go.

Anyway.....our county just switched over to a brand new 800 MHz Smartzone Digital system.

How do you get people (in high places) to realize the potential disasters associated with relying on a digital trunking system for fireground operations.

Reasons for not doing so:
-ties up the system
-may not be able to hit a tower while inside a structure fire situation (especially when the radio is down in your turn-out-gear)
-digital sucks
-delay
-other misc

I feel like someone should address this, but it could be taken the wrong way by the powers that be.......

HELP!!!!!!!

Wes

[fireradio]

I live in the DC Metro Area of Virginia, and my county plus the five or six other surrounding counties/cities all have 800 systems and they all use trunked talkgroups (some digital, some analog, depending on the county) for fireground ops. Of course, we also have two simplex channels which are used from time to time when in-building coverage is not good enough, but 90% of the time (or more) the trunked channels are used.

[ExKa|iBuR]

Here in Toronto, we have a 4 zone SmartZone analog trunking system with multiple receiver sites. The Fire Department does have 6 talkaround simplex frequencies that from time to time they will patch in with a talkgroup, they'll ask dispatch to turn on the fireground repeater. This hardly ever happens unless they are inside a highrise apartment or deep underground. I'd say that 95% of the calls that TFS respond to keep everything on the trunking system, and I've rarely ever heard a coverage issue.

While I understand the need to stay conventional, why should digital matter? It's simply another form of modulation, which is far superior, in my opinion.

-M

[Tom in D.C.]

The best single reason for using simplex is that it's the most reliable form of communication. The only reason it's not used at greater distances is the fact that its failing is that it won't work at greater distances. Other than that it beats repeater operation hands down.

The primary reason for using simplex ANALOG would obviously be interoperability. A mutual aid company from the next county with an LTR system (or anything else other than P25) need only be on, say, 153.950 analog same as your 153.950 analog channel and everyone can talk to everyone else.

Wes, this issue obviously needs a lot more publicity. Thanks for making a big point about it. I've been talking about it since it became NFPA's recommendation. I think it's just common sense.

[RKG]

There was an incident on FDNY about two years ago, now fairly famous in FD radio circles, where a jake in the basement of a building in need of assistance and armed with an Astro Saber, was unable to be heard by the rest of his company a few feet away on the sidewalk, though he was heard by someone 10-15 blocks away. The conclusion is that digital modulation in the near field has a high risk of failure for reasons that are quite complicated and still a matter of speculation. I was told that 1221 was going to be modified to specify analog only on the fireground and thought it had. I'll have to check at the station to see what the latest version is (if I remember).

[Wes]

Tom,

You are exactly right. It is common sense to see that analog conventional simplex is the most reliable form of fireground communication.

Not only does it not tie up a system, it doesnt force the fireground communicatios to rely on a tower site or repeater site far away from the scene. It does not make sense to talk on a repeater or trunked system to cover a fireground that most of the time is an area no larger than a 100' radius.......WTF????

Also as you stated, it is the greatest form of interoperability. Not all trunking/digital systems are compatable, but show me one radio that doesent allow for conventional simplex analog.

I agree that most of the time the fireground could be worked on a repeater or trunked system, but we all know that the chance is there that it will not cover, do we really want to be taking that chance when our lives are on the line? I know I dont!!

Tom, thanks for the good comments on this serious issue.

Wes

[nmfire10]

I agree with everyone who has spoken againt using digital, talkgroups, or repeaters for interior operations. Our neighboring town just put in a new repeater system. The fireground radios have DIRECT as channel 1. That should tell you something.

[Fuel4300]

There was an incident on FDNY about two years ago, now fairly famous in FD radio circles, where a jake in the basement of a building in need of assistance and armed with an Astro Saber, was unable to be heard by the rest of his company a few feet away on the sidewalk, though he was heard by someone 10-15 blocks away. The conclusion is that digital modulation in the near field has a high risk of failure for reasons that are quite complicated and still a matter of speculation. I was told that 1221 was going to be modified to specify analog only on the fireground and thought it had. I'll have to check at the station to see what the latest version is (if I remember).

I believe it was an XTS3500 but your point still stands. However, this was in the first few months these radio were being implimented and they met with much resistence in some circles (We all know how hard some of us will fight for whatever reason against change even when its in our best interest) and the stories of their problems, this one in particular, may have been somewhat exaggerated.

In my home department we use an analog UHF system and we had an instance where crews were attacking a fire in a old diner consisting of a couple double wides with a common truss roof and the repeater went down. This system was only about a year old and the problem may have been intermittant before hand but at this time the crews inside were unable to recieve calls from chief officers that the fire was thru the roof.

Needless to say, all interior operations are now conducted on simplex.

Mike

[RKG]

The FDNY UFA claimed that the incident in question demonstrated the inadequacy of the XTS3500s, concerning the procurement of which they were upset, but I'm told by a source I trust that the actual portable in the actual incident was an Astro Saber. (FDNY uses VHF for dispatch and UHF for fireground and interagency stuff.)

[spareparts]

I have noticed a couple of threads on the board and have seen some comments in reference to the NFPA 1221 standard on communications.....
I obtained a copy of the must current version (2002) and checked it out. I totally agree with what it says which is basically "Do not use trunking talkgroups for tactical on-scene operations."

While at an NFPA training seminar today, I had a chance to chat with one of the members of the group that updated NFPA 1221. Do you have the citatation handy so I can ask if they actually meant "no analog trunking or no trunking (including digital).

Martin

[RADIOMAN2002]

If you want some real world experiences contact the FDNY, the jerk that used to be Fire Commisioner, forced their radio shop to switch all there operations to digital, with out any field trials or testing,and it failed miserably, so bad the FD members went public about .There are more threads about it on Batlabs,and other boards, do a little reasearch, and give the mucky mucks the copies. This was before 911.and eventually, Motorola who was the vendor denied any problems with their radios, but was happy to sell the FDNY all new ones.Which the FDNY radio proptly programmed for analog operations.

[RocketNJ]

The FDNY UFA claimed that the incident in question demonstrated the inadequacy of the XTS3500s, concerning the procurement of which they were upset, but I'm told by a source I trust that the actual portable in the actual incident was an Astro Saber. (FDNY uses VHF for dispatch and UHF for fireground and interagency stuff.)

I was an XTS3500 programmed for digital operation. Problem with that is a typical scene involves at least 25 people there, each with his own radio. You wind up with different teams trying to transmit at the same time and in digital operation that results in nothing being heard. So add radio etiquette to the list as a reason not to use digital for fireground.

[jim]

Another thing to remember is that with digital, it's all or nothing. There's no static in the audio when you get a low signal. A few data bits get lost, you have no audio. With analog, you get slight static or hiss when you lose some signal, but it is still legible.

[Pj]

Actually, when you are on the fringe range, you get packet loss, and it gets more "digital" sounding. The error correction does work pretty well. With out dept testing, we find that we get understandable audio a little more in the digital mode than analog in side-by-side testing.

The scanner in the PD pretty much quits with the audio as you descibe, but my AS3 and the dept XTS3000's don't experience this (all DSP8).

[MattSR]

I love all these people that talk about "packet loss" with ASTRO radios...

It's just a pity that ASTRO isnt even a packetised protocol - its synchronous...

[mt1000ff]

I dont have the standard in front of me but if memory serves it says fire groung ops should not be trunked, but can be repeated, I dont think it mentions simplex. Also I think it says that fire ground ops should be recorded and monitored by the dispatch.

Tim

[Wowbagger]

I love all these people that talk about "packet loss" with ASTRO radios...

It's just a pity that ASTRO isnt even a packetised protocol - its synchronous...

If, by ASTRO, you mean "SmartNet 3600 bps control channel with a 9600 bps APCO-25 voice channel", then yes it IS packetized - the voice is sent as packets of audio (LDU1 and LDU2).

However, losing "a few bits" is NOT enough to corrupt the signal - there's about as much forward error correction bits as there are actual data bits in APCO-25, so you need a pretty damn high bit error rate before you see corruption - in fact, one of the standard tests for APCO-25 voice channels is to feed a 5% BER signal to the radio - which should have no problems decoding it.