Afterthought:
NFPA (I don't remember the standard number) recommends that dispatch agencies with more than (about) 800 paged incidents a year use the following:
1. All alerts are transmitted on a dedicated, one-way signalling (paging) channel. That channel is not used for resource alerting acknowledgements or other voice traffic.
[Since there is no reply traffic from alerted resources, you gain the ability to record and automatically replay all alert transmissions without fear of "walking on" an acknowledgement. In addition, new or additional pages are not delayed waiting on voice traffic from resources, or visa-versa. Plain old stupid vanilla analog works just fine.
In my 'home' system the first page goes out locally to the agency being alerted, then is automatically replayed from a central transmitter with decent universal coverage.]
2. Alert acknowledgements, communication between Dispatch and all responding units, distance communication, and Command and Control generally take place on a second channel.
[This can be analog simplex, repeated, trunked, digital, 39 MHz, 800 MHz or any other system that works for you. Failures are typically short, and since this traffic is not generally Life and Safety urgent can be re-sent if it wasn't understood the first time.]
3. Life and Safety Critical fire ground and tactical communications take place on a third simplex channel that is a basic as possible.
[Look at the MABAS-IL model. No repeaters, no encryption, no anything that might prevent a weak mayday call from going 200 yards. And also, no off-scene transmitters that cannot hear a weak on-scene traffic and walk over a mayday call with non-critical traffic. Personally, I think that even adding a digital vocoder into the Life and Safety Critical path adds an un-necessary point of failure.]
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Opinion:
Following the above standard, you can use VHF analog pagers, use a digital trunked system for Command and Control, then go to plain old stupid vanilla (bulletproof) analog for Life and Safety traffic as long is it will get from one side of an incident to the other without relying on infrastructure.
If your pager goes off, you've been notified. If that happens 99% of the time, you're doing great. Now switch to a system that handles wide area voice traffic more reliably.
On scene, switch again. FF's on the wet end of the hose do not need to hear that lunch is on the way or another alarm went out.
Every white helmet comes with a radio for each hand. Priority is always Life and Safety. If the C&C radio fails someone can tap the IC on the shoulder.
A mayday call should never be forced to travel to a distant tower, be handled, folded and translated, then sent back to within a hundred yards of where it started. That's okay for taxis and ordering more fuel, but overkill when your feet have fallen through the floor.
If off-scene monitoring or recording of Life and Safety Critical traffic is desired, use infrastructure to repeat it, but do not rely on the infrastructure to handle any mayday call. If you review FF LODD reports, there are far too many fatalities caused or contributed by mayday calls getting bonked off an infrastructure system, or not be heard by others on-scene due to off-channel interference muting digital cries for help.
Never forget the sneaky ability of receiver desense to cause problems.
NFPA (I don't remember the standard number) recommends that dispatch agencies with more than (about) 800 paged incidents a year use the following:
1. All alerts are transmitted on a dedicated, one-way signalling (paging) channel. That channel is not used for resource alerting acknowledgements or other voice traffic.
[Since there is no reply traffic from alerted resources, you gain the ability to record and automatically replay all alert transmissions without fear of "walking on" an acknowledgement. In addition, new or additional pages are not delayed waiting on voice traffic from resources, or visa-versa. Plain old stupid vanilla analog works just fine.
In my 'home' system the first page goes out locally to the agency being alerted, then is automatically replayed from a central transmitter with decent universal coverage.]
2. Alert acknowledgements, communication between Dispatch and all responding units, distance communication, and Command and Control generally take place on a second channel.
[This can be analog simplex, repeated, trunked, digital, 39 MHz, 800 MHz or any other system that works for you. Failures are typically short, and since this traffic is not generally Life and Safety urgent can be re-sent if it wasn't understood the first time.]
3. Life and Safety Critical fire ground and tactical communications take place on a third simplex channel that is a basic as possible.
[Look at the MABAS-IL model. No repeaters, no encryption, no anything that might prevent a weak mayday call from going 200 yards. And also, no off-scene transmitters that cannot hear a weak on-scene traffic and walk over a mayday call with non-critical traffic. Personally, I think that even adding a digital vocoder into the Life and Safety Critical path adds an un-necessary point of failure.]
-----
Opinion:
Following the above standard, you can use VHF analog pagers, use a digital trunked system for Command and Control, then go to plain old stupid vanilla (bulletproof) analog for Life and Safety traffic as long is it will get from one side of an incident to the other without relying on infrastructure.
If your pager goes off, you've been notified. If that happens 99% of the time, you're doing great. Now switch to a system that handles wide area voice traffic more reliably.
On scene, switch again. FF's on the wet end of the hose do not need to hear that lunch is on the way or another alarm went out.
Every white helmet comes with a radio for each hand. Priority is always Life and Safety. If the C&C radio fails someone can tap the IC on the shoulder.
A mayday call should never be forced to travel to a distant tower, be handled, folded and translated, then sent back to within a hundred yards of where it started. That's okay for taxis and ordering more fuel, but overkill when your feet have fallen through the floor.
If off-scene monitoring or recording of Life and Safety Critical traffic is desired, use infrastructure to repeat it, but do not rely on the infrastructure to handle any mayday call. If you review FF LODD reports, there are far too many fatalities caused or contributed by mayday calls getting bonked off an infrastructure system, or not be heard by others on-scene due to off-channel interference muting digital cries for help.
Never forget the sneaky ability of receiver desense to cause problems.
