Busy Channel Lock-Out

[JethrowJohnson]

My police department has an analog conventional radio system, but why don't they have the BCLO feature, and if they should, then would there be a big reason not to use it? And, on a P25 system, does that feature just work automatically, or could units step on each other with that kind of system too?

 

[mmckenna]

My police department has an analog conventional radio system, but why don't they have the BCLO feature, and if they should, then would there be a big reason not to use it?

Because something simple like localized interference would prevent an officer from transmitting. Good idea, but in reality, it's better to deal with the multiple units keying up at the same time.

And, on a P25 system, does that feature just work automatically, or could units step on each other with that kind of system too?

On a trunked system, subscriber units would get a "bonk" from the system if they tried to both key up on the talkgroup at the same time. There are some ways to set priority, but that gets into a whole discussion.

 

[JethrowJohnson]

Thank you. That answers my question perfectly! 🙂👍

 

[speedway_navigator]

A few years ago in San Diego the PD had surrounded a home where a man was seen breaking into the front door with a gun.
They setup a perimeter and were getting motor units and volunteer units in to block traffic. The volunteers are usually retired folks without law enforcement experience from what I've gathered and it shows when the get on the radio.

One of the units was describing their approach to the scene and suddenly an officer broke in and said he needed cover because the suspect was climbing out a rear window with gun in hand. BCLO would have prevented that.

 

[JethrowJohnson]

A few years ago in San Diego the PD had surrounded a home where a man was seen breaking into the front door with a gun.
They setup a perimeter and were getting motor units and volunteer units in to block traffic. The volunteers are usually retired folks without law enforcement experience from what I've gathered and it shows when the get on the radio.

One of the units was describing their approach to the scene and suddenly an officer broke in and said he needed cover because the suspect was climbing out a rear window with gun in hand. BCLO would have prevented that.

Are they on a trunked system or conventional system?

 

[AM909]

Talking about P25, I imagine "emergency mode" can be set to have priority, but is there another way to allow the subscriber to send a priority transmission without hitting the orange button? Sort of an "urgent but not emergent" button that doesn't trigger emergency features like silencing RX audio and tones, always-hot mic, etc.

 

[speedway_navigator]

Are they on a trunked system or conventional system?

They were on a trunked system. The volunteer unit radios might have been programmed with lower access priority.

 

[KevinC]

They were on a trunked system. The volunteer unit radios might have been programmed with lower access priority.

Interesting. How did they interrupt the call in progress on a trunked system?

 

[JethrowJohnson]

Talking about P25, I imagine "emergency mode" can be set to have priority, but is there another way to allow the subscriber to send a priority transmission without hitting the orange button? Sort of an "urgent but not emergent" button that doesn't trigger emergency features like silencing RX audio and tones, always-hot mic, etc.

I think on trunked systems, the dispatcher can set specific units for priority so they can preempt other traffic, but I'm not really sure. @mmckenna I have a new question. 😉

 

[JethrowJohnson]

They were on a trunked system. The volunteer unit radios might have been programmed with lower access priority.

I was wondering, because usually on analog conventional systems, if one unit interrupts another you'll only hear a scrambly noise because the radio waves are cancelling each other out since they're the same frequency. But you might hear one of them if it's stronger than the other one.

 

[mrsvensven]

Interesting. How did they interrupt the call in progress on a trunked system?

It's called ruthless preemption. On a p25 phase 1 talkgroup, when an emergency button is pressed during a voice call, the system abandons the voice call in progress and assigns a second voice channel. All radios are sent over to that new voice channel and the user with the emergency is allowed to talk. The only radio that doesn't hear the emergency call is the first radio that was originally transmitting, because that radio is actively transmitting and not monitoring the control channel.

On p25 phase 2 talkgroups, the radios transmit and receive simultaneously, so that first radio will actually get a bonk mid-transmission to let that user know that nobody is listening to them any more.

 

[KevinC]

It's called ruthless preemption. When an emergency button is pressed during a voice call, the system abandons the voice call in progress and assigns a second voice channel. All radios are sent over to that new voice channel and the user with the emergency is allowed to talk. The only radio that doesn't hear the emergency call is the first radio that was originally transmitting, because that radio is actively transmitting and not monitoring the control channel.

Ok, but nothing was said about pushing the emergency button. I wouldn’t have asked if it was.