mtnmadman
Member
So what happens if the 800 systems go down? i know there is a fail safe set up, but is there a vhf back up?Just wondering...
800 meg question?
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WA0CBW
Member
That would depend on if there were any other radios (VHF/UHF/??) in the cars. A backup system on VHF or UHF doesn't do any good if there is no VHF/UHF radio in the vehicles.
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There are several levels of failure in a trunked system. Search for the terms "site trunking" and "failsoft" in the RR wiki or google and you will find all you need to know. If the system fails catastrophically, then the users have to resort to conventional repeaters (if available) or simplex. I am not sure how many agencies have a failure protocol that goes that far, but they should.
mtnmadman
Member
Ya, i dont know if there is vhf back up in all the units.. Im going to guess not due the expense. I dont think its goin to go down, i think the disp.has had more problems with their CAD systems lately
mtnmadman
Member
Thanks!!
avdrummerboy
Member
All of our ambulances have an 800 Mhz radio as well as a VHF and UHF radio. The trunked system has a lot of failsafe built in, but if for whatever reason the 800's went down catostrophically, there is still 'D' or direct mode in 800 Mhz as well as a slew of VHF frequencies to use (Sheriff doesn't have any that I know of, but Commcenter does, county 1-4.) That is assuming, of course, that what ever catastrophic even that took down the 800 system didn't also take out the VHF towers or systems! Our company also has a UHF system that can be used locally for small level stuff in that event.
There really is no backup. The fire VHF stuff is pretty sparse, and doesn't do stuff like station call alerting. For other 800 users, they don't even have that.
What happens when 800 goes down really depends on why and where it went down. A console failure can be worked around with the mobile radio installed at each console position. A prime site controller failure will cause a failsoft condition, and users revert to conventional operation. Loss of a site will create a coverage hole, but the rest of the system will keep working. Loss of a trunked channel usually goes unnoticed by users.
There are other failure modes that can happen with various results ranging from " ho hum" to "we're screwed". Microwave failures, power failures, vandals, etc... They all hit the systems in different places, so the end result will be different.
avdrummerboy
Member
You'd probably know better than I can guess zz0468, when the systems go into failsoft mode, obviously there are only a limited number of conventional channels that can be assigned, how are they allocated, some sort of priority system, fire/ law/ ems getting first dibs on channels, ACO, roads, flood control and others left behind?
The failsoft channels are assigned by agency and use. Each law enforcement agency would have all its talk groups share a failsoft channel. County fire would get a channel. Public works agencies like road and parks would share a channel.
So, critical users get their own channel while non critical users end up sharing with other non critical users. How generous the fs channel assignments can be would depend on the number of channels in the system, and loading.
So, critical users get their own channel while non critical users end up sharing with other non critical users. How generous the fs channel assignments can be would depend on the number of channels in the system, and loading.
avdrummerboy
Member
That makes sense, a small system would have to consolidate a lot more than a larger system.
mtnmadman
Member
that helps a lot thank you
It also depends (like zz stated) on where the failure occurs. For example in SBCo, the 8-system "could-be" used as a backup to both the 1-system in the Victor Valley as well as the 6-system in the SB valley. However, having the entire multi-site / simulcast 6-system fail would be rare.
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