site question

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squad1b

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do i need both the Alternate and control channels to make a scanner pick up talk groups properly.trying to get MPLS FIRE.

Scott
thanks in advance for your help
 
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stmills

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It is not needed but is a good idea. The alternate control channels only come into play if the main channel goes offline. Hennepin Systems used to switch to an alternate for about 1 day per month, but this stopped a couple system upgrade ago.
 

troymail

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Steve probably knows better since he is in your area.

However, "generically", depending upon the system and other factors, the system could switch to a different control channel frequency at any time and without notice (other than "hey, it just got really quiet!").

You can operate on only the current control channel for most P25 and Motorola system/sites but it's probably better to program the primary and alternates. Having said that, there are some system/sites where you really have to program ALL system frequencies because the CC moves around alot.

Then, there are some system/sites (simulcast) where your radio might perform better by only programming the active CC frequency.

It's not a one size fits all.
 
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Project25_MASTR

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Depending on who makes the system, really signifies what channels should be programmed. Typically, Harris systems any channel at a site can be an alternate control channel so if there is a failure of the active control channel the scanner may not pickup the alternate that become the control if only the active is programmed.

Now with Motorola, you will only have 4 advertised control channels, one active and three alternates. Motorola does this as with their site setups, there are two controllers, and two switches (typically). One controller is plugged into one switch along with all odd numbered channels while the other switch has the second controller and even numbered repeaters. If the primary control channel fails, the system will designate the secondary (which is typically an even numbered repeater). If a switch fails, Site Capacity is halved and there are still a primary and secondary control capable repeater at the site.

With a scanner, the only other time you’d truly want all channels of a system (apart from a Harris setup) is for failsoft but I don’t exactly know how a scanner would handle failsoft.


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troymail

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With a scanner, the only other time you’d truly want all channels of a system (apart from a Harris setup) is for failsoft but I don’t exactly know how a scanner would handle failsoft.


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For scanners, you'd have to have the frequencies programmed as conventional - and then know the site/system failed and manually switch over to that programming on your radio.

It might be a cool feature (!) to allow for a trunk system to be programmed (as an option) such that the scanner automatically started using the trunked system/site frequencies as conventional (and go into some type of visual/audible alarm status) if/when the control channel is lost. Of course, for many scanner users, they'd probably be switching to "pseudo failsoft" alot given that it is a scanner and can't always find the control channel (mobile applications, simulcast problems, etc,). But that's why it should be an "option" for the user (like, for example, whether or not I want to know and hear encrypted talkgroups).

For now - it's "have a scanlist programmed as conventional" and know there is a problem ... which may be really hard to do - I've missed "silence" on really busy systems sometimes because in many cases, it's just another thing I'm hearing -or not- "in the background").

EDIT: not sure about P25 Phase 2 and failsoft - I assume the system reverts to conventional P25 Phase 1(FDMA).. reducing capacity by 50% - and kicking some users off completely (or they become so low on the priority they don't get airtime) due to that reduced capacity. I suspect things like public works might probably get prohibited in failsoft but of course, it all depends on the system.
 
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jaspence

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I have an XT3000 programmed with just the frequencies actually used, and it works like a basic scanner. Great quality, but no trunking, and transmit inhibit is on to avoid any problems if I accidentally hit the PTT..
 

Project25_MASTR

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For scanners, you'd have to have the frequencies programmed as conventional - and then know the site/system failed and manually switch over to that programming on your radio.



It might be a cool feature (!) to allow for a trunk system to be programmed (as an option) such that the scanner automatically started using the trunked system/site frequencies as conventional (and go into some type of visual/audible alarm status) if/when the control channel is lost. Of course, for many scanner users, they'd probably be switching to "pseudo failsoft" alot given that it is a scanner and can't always find the control channel (mobile applications, simulcast problems, etc,). But that's why it should be an "option" for the user (like, for example, whether or not I want to know and hear encrypted talkgroups).



For now - it's "have a scanlist programmed as conventional" and know there is a problem ... which may be really hard to do - I've missed "silence" on really busy systems sometimes because in many cases, it's just another thing I'm hearing -or not- "in the background").



EDIT: not sure about P25 Phase 2 and failsoft - I assume the system reverts to conventional P25 Phase 1(FDMA).. reducing capacity by 50% - and kicking some users off completely (or they become so low on the priority they don't get airtime) due to that reduced capacity. I suspect things like public works might probably get prohibited in failsoft but of course, it all depends on the system.



I see some issues with that as when a site goes into failsoft, all repeaters begin transmitting so the only way to differentiate traffic would be via talkgroup. Not knowing exactly how the scanner scans P25 exactly when in conventional, it may hang up on one of those channels even though no voice traffic is being passed.


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troymail

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I see some issues with that as when a site goes into failsoft, all repeaters begin transmitting so the only way to differentiate traffic would be via talkgroup. Not knowing exactly how the scanner scans P25 exactly when in conventional, it may hang up on one of those channels even though no voice traffic is being passed.


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I know what you mean. When scanning some P25 frequencies in conventional mode, it sometimes seems like there is an open/idle carrier on some frequencies. Radios would have to be smart enough to detect this and ignore it.
 
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