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Conventional P25 Frequency

JethrowJohnson

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Is it possible to have the emergency priority preemption feature on a P25 conventional frequency like they do on a P25 trunked talkgroup?
 
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JethrowJohnson

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So, for example, the Wood County Sheriff's Office in West Virginia uses a conventional P25 frequency, so if unit 18 was running a registration plate to the dispatcher and unit 20 pressed his emergency button while 18 was still transmitting, 20 would be able to interrupt all other traffic on the channel even though the system isn't controlled by a computer?
 

MILCOMM

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So, for example, the Wood County Sheriff's Office in West Virginia uses a conventional P25 frequency, so if unit 18 was running a registration plate to the dispatcher and unit 20 pressed his emergency button while 18 was still transmitting, 20 would be able to interrupt all other traffic on the channel even though the system isn't controlled by a computer?


If the network has open resources at this moment, I get instant ownership of
those resources. If the network has no open resources at this moment, I get instant ownership of someone
else’s resources; they get ruthlessly denied service on the system. This preemption exists for a short period of
time, such as 10 seconds for emergency voice, or until the radio is reset by the user for normal use.
 

KevinC

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So, for example, the Wood County Sheriff's Office in West Virginia uses a conventional P25 frequency, so if unit 18 was running a registration plate to the dispatcher and unit 20 pressed his emergency button while 18 was still transmitting, 20 would be able to interrupt all other traffic on the channel even though the system isn't controlled by a computer?

Negative. You could do it with DMR though.
 

JethrowJohnson

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The emergency priority preemption feature is of short duration. If an officer employed it,
I think the other 18 officers would be responding to his aid.
They would, but if unit 18 was running a plate, and at the same time, some fool tried to shoot at unit 20, and unit 20 started chasing him (from a distance of course) then 20 would only have Priority for ten seconds and after that, if he needed to give a direction of travel but everyone else was tying up the air with all these questions out of panic, then unit 20 wouldn't be able to get on the air? Just trying to clarify.
 

MILCOMM

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They would, but if unit 18 was running a plate, and at the same time, some fool tried to shoot at unit 20, and unit 20 started chasing him (from a distance of course) then 20 would only have Priority for ten seconds and after that, if he needed to give a direction of travel but everyone else was tying up the air with all these questions out of panic, then unit 20 wouldn't be able to get on the air? Just trying to clarify.


An emergency call is for the dispatcher and the emergency alarm is to a group and is just an alert
to let others know an emergency or some sort of priority exists. Other units would be able to communicate.
 

mmckenna

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On a conventional P25 repeater (non-trunked), the the channel is tied up if someone is transmitting, and it would be unlikely the other traffic would get through.
On a trunked system, the officer could hit an 'emergency' button on the radio that would signal through the control channel that he/she had an emergency.

They would, but if unit 18 was running a plate, and at the same time, some fool tried to shoot at unit 20, and unit 20 started chasing him (from a distance of course) then 20 would only have Priority for ten seconds and after that, if he needed to give a direction of travel but everyone else was tying up the air with all these questions out of panic, then unit 20 wouldn't be able to get on the air? Just trying to clarify.

Dispatchers and other officers would hear the traffic. Dispatchers usually have a button they can press that sends out a periodic tone on the channel. That tone indicates to the other officers that there is something going on and they need to keep their yaps shut.
It's a discipline thing. No officer would start running a plate for someone who rolled a stop sign in a situation like that.
 

JethrowJohnson

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On a conventional P25 repeater (non-trunked), the the channel is tied up if someone is transmitting, and it would be unlikely the other traffic would get through.
On a trunked system, the officer could hit an 'emergency' button on the radio that would signal through the control channel that he/she had an emergency.



Dispatchers and other officers would hear the traffic. Dispatchers usually have a button they can press that sends out a periodic tone on the channel. That tone indicates to the other officers that there is something going on and they need to keep their yaps shut.
It's a discipline thing. No officer would start running a plate for someone who rolled a stop sign in a situation like that.
Okay. Thank you, that answers my question. (The officer running the plate was just before the emergency though) 👍
 

mmckenna

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Okay. Thank you, that answers my question. (The officer running the plate was just before the emergency though) 👍

Right, and until officer running the plate gets off the radio, officer in trouble has to wait.
But, you'll often find that a well trained officer will avoid making long winded transmissions, and if they need to, they'll often "break", let go of the PTT button, wait a few seconds, and continue.
 

GTR8000

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This is one major advantage of TDMA technology. I know P25 P2 operates like this, and possibly DMR trunking as well. Not only does someone hitting the emergency button preempt traffic on the talkgroup, but with TDMA the system can also instruct the transmitting subscriber to stop transmitting, which is something that cannot be accomplished with FDMA technology.

The key is that when a subscriber is transmitting in TDMA mode, it's transmitting in 30ms bursts, and every couple of bursts it listens to signaling on the other slot. Some of the messages it might receive are to stop transmitting because of an emergency, stop transmitting due to going out of range, adjust power based on how well/poorly it's getting inbound, and to receive voice traffic if a dispatcher/console preempts them. P25 P2 ain't cheap, but it does come with some notable benefits aside from just doubling traffic channel capacity without adding more frequencies.
 

KevinC

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This is one major advantage of TDMA technology. I know P25 P2 operates like this, and possibly DMR trunking as well. Not only does someone hitting the emergency button preempt traffic on the talkgroup, but with TDMA the system can also instruct the transmitting subscriber to stop transmitting, which is something that cannot be accomplished with FDMA technology.

The key is that when a subscriber is transmitting in TDMA mode, it's transmitting in 30ms bursts, and every couple of bursts it listens to signaling on the other slot. Some of the messages it might receive are to stop transmitting because of an emergency, stop transmitting due to going out of range, adjust power based on how well/poorly it's getting inbound, and to receive voice traffic if a dispatcher/console preempts them. P25 P2 ain't cheap, but it does come with some notable benefits aside from just doubling traffic channel capacity without adding more frequencies.

Every 9th time slot, so about every 270 milliseconds.
 

JethrowJohnson

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This is one major advantage of TDMA technology. I know P25 P2 operates like this, and possibly DMR trunking as well. Not only does someone hitting the emergency button preempt traffic on the talkgroup, but with TDMA the system can also instruct the transmitting subscriber to stop transmitting, which is something that cannot be accomplished with FDMA technology.

The key is that when a subscriber is transmitting in TDMA mode, it's transmitting in 30ms bursts, and every couple of bursts it listens to signaling on the other slot. Some of the messages it might receive are to stop transmitting because of an emergency, stop transmitting due to going out of range, adjust power based on how well/poorly it's getting inbound, and to receive voice traffic if a dispatcher/console preempts them. P25 P2 ain't cheap, but it does come with some notable benefits aside from just doubling traffic channel capacity without adding more frequencies.
If that only works in TDMA mode, then why was a Columbus Ohio officer able to preempt everyone when he was pursuing a wanted felon? I was listening to it on the Columbus Division of Police - Citywide feed and after the dispatcher put the channel in emergency mode, he was able to interrupt everyone including the dispatcher when he needed to give an update. And MARCS is only a P25 Phase I system.
 

GTR8000

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If that only works in TDMA mode, then why was a Columbus Ohio officer able to preempt everyone when he was pursuing a wanted felon? I was listening to it on the Columbus Division of Police - Citywide feed and after the dispatcher put the channel in emergency mode, he was able to interrupt everyone including the dispatcher when he needed to give an update. And MARCS is only a P25 Phase I system.
Hitting the emergency button to put the talkgroup into emergency mode is different from what I posted. I'm talking about a subscriber that is actively transmitting can be preempted with TDMA, i.e. will be instructed to stop transmitting. Apples and oranges.
 

JethrowJohnson

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Hitting the emergency button to put the talkgroup into emergency mode is different from what I posted. I'm talking about a subscriber that is actively transmitting can be preempted with TDMA, i.e. will be instructed to stop transmitting. Apples and oranges.
So, you mean that on an FDMA system, if one unit is TX and another unit presses his/her emergency button, then the emergency unit can talk, but the first one would still be transmitting too, therefore they'd both be talking at once?
 

GTR8000

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So, you mean that on an FDMA system, if one unit is TX and another unit presses his/her emergency button, then the emergency unit can talk, but the first one would still be transmitting too, therefore they'd both be talking at once?
No. The one that was transmitting would still be "in transmit mode", but the system would simply ignore that radio and would pass traffic from the emergency radio. The point is that the first radio would have no awareness of what is going on, since a subscriber in FDMA mode cannot both transmit and monitor like it could in TDMA mode.

Oh and as far as radios and consoles talking at the same time, the system consoles are setup to mimic "4 wire" operation, meaning that even while the dispatcher is talking, he can still receive and hear transmissions from the subscribers. This is because the consoles are transmitting through the repeaters in "base station" mode, not using the repeater inputs as would be the case with a conventional repeater. If a subscriber keys up while a dispatcher is transmitting, that audio would be heard on the consoles, and is often heard bleeding through the dispatcher's microphone.
 

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Oh and as far as radios and consoles talking at the same time, the system consoles are setup to mimic "4 wire" operation, meaning that even while the dispatcher is talking, he can still receive and hear transmissions from the subscribers. This is because the consoles are transmitting through the repeaters in "base station" mode, not using the repeater inputs as would be the case with a conventional repeater. If a subscriber keys up while a dispatcher is transmitting, that audio would be heard on the consoles, and is often heard bleeding through the dispatcher's microphone.

Talkunder. And apparently EDACS didn’t have that feature and many agencies transitioning from it to Motorola think something is wrong and the field units are talking over the dispatcher. Been there, done that.
 

JethrowJohnson

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No. The one that was transmitting would still be "in transmit mode", but the system would simply ignore that radio and would pass traffic from the emergency radio. The point is that the first radio would have no awareness of what is going on, since a subscriber in FDMA mode cannot both transmit and monitor like it could in TDMA mode.

Oh and as far as radios and consoles talking at the same time, the system consoles are setup to mimic "4 wire" operation, meaning that even while the dispatcher is talking, he can still receive and hear transmissions from the subscribers. This is because the consoles are transmitting through the repeaters in "base station" mode, not using the repeater inputs as would be the case with a conventional repeater. If a subscriber keys up while a dispatcher is transmitting, that audio would be heard on the consoles, and is often heard bleeding through the dispatcher's microphone.
Ah, I see. Well, now I can't wait for MARCS to get the Phase II upgrades that the database mentions. Thanks for helping me understand this stuff better.
 

BMDaug

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Most radios also allow you to set a specific emergency channel. This would allow officers to talk on whatever channel they need to be on, but hitting emergency defaults to one specific channel, which could be a solution of sorts in a P25 conventional system. Other units still won’t know until the dispatcher initiates an emergency tone, but it would potentially allow the officer in emergency to gain some sort of priority.

-B
 

mrsvensven

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So, you mean that on an FDMA system, if one unit is TX and another unit presses his/her emergency button, then the emergency unit can talk, but the first one would still be transmitting too, therefore they'd both be talking at once?
Yes, that's how it works. The emergency radio keys up and is granted a different voice channel. The consoles and all other radios will switch to the new voice channel being used by the emergency radio and will hear the emergency traffic. Because the first transmitting radio can't receive anything while activly transmitting, it keeps transmitting even though nobody else can hear them any more.
 
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