Check for open mic .... ??

[wlmr]

As far as I'm aware, there aren't any trunked systems, conventional repeated systems, or simplex systems that use full duplex radios for the people in the field. (Full duplex = they can transmit and still receive at the same time.) The base stations the dispatchers control are another story.

So, for the most part, the "all units please check for an open mic" never is received by the radio that is keyed. A field unit that has both a portable and is sitting in a car with a radio has the chance of hearing the dispatcher broadcast this message.

In the trunking system I'm familiar with the radio with the open mic cannot hear anything said by anyone while keyed. Other units on that same talkgroup (including the mobile radio in the car if it's an officer sitting on his portable) will be told via data from the system on the original voice frequency to switch to a different frequency on the site to hear the dispatcher's message.

The ability to inhibit or regroup the "stuck" radio can be sent while that radio is still transmitting but the stuck radio WON"T receive and act on it until the timer in the radio makes the radio unkey. Then the radio gets dealt with. I've yet to see any radio in the field, simplex through to trunked that the radio tech's who program it haven't set the radio to unkey (and set off a loud tone) after a set amount of time. I've seen from 30 seconds to 3 minutes, rarely longer. Of course, if the PTT button is in a location where as the vehicle bounces it keys and unkeys means that the timer may never get activated.

So either the dispatcher has to hope for the 2nd radio hearing the announcement. (If it is a 2 person car the other portable counts also.) -OR-
The dispatcher may be waiting for those gaps in the stuck radio's keyups and hoping that they get the message.

Again I've not seen full duplex radios carried in the vehicles or as portables. I'm not saying they don't exist, just highly unlikely as slicerwizzard correctly points out. Cellular phones are a completely different system so I'm staying away from discussing them, we're talking two-way radio systems here.

 

[slicerwizard]

In the trunking system I'm familiar with the radio with the open mic cannot hear anything said by anyone while keyed. Other units on that same talkgroup (including the mobile radio in the car if it's an officer sitting on his portable) will be told via data from the system on the original voice frequency to switch to a different frequency on the site to hear the dispatcher's message.

Have you actually verified this? If so, how? Why would they have to switch to another frequency when the dispatcher can talk over or mute the audio from the offending radio?

 

[bwhite]

My sister is a police dispatch supervisor for a large 911/dispatch center using a trunked system, she's been telling me for years that if they have an open mic they can send a command to shut the offending radio up. Undoubtedly it is something transmitted on the control channel that the radio is ALWAYS receiving even while transmitting. If it is a trunked system they do not switch to a diff frequency as frequencies are transparent to units in such a system, talkgroups are the key.

 

[exkalibur]

What the hell are you smoking?

A radio CANNOT receive at the same time it is transmitting. At least, not any radios we'd be dealing with. Some technologies like cellphones and the like can TX and RX at the same time, but for the time being, what you are describing is impossible.

Frequencies are not transparent on a trunking system. A trunking system still has a bunch of repeaters on different frequencies - the only difference is that a computer selects the voice repeater to be used for communications.

Your sister might want to re-check her training, because if what you're saying is what she told you, she's sadly mistaken. If a radio is transmitting an open carrier, there is NO WAY for the dispatcher to remotely shut it down. Period.

 

[slicerwizard]

she's been telling me for years that if they have an open mic they can send a command to shut the offending radio up. Undoubtedly it is something transmitted on the control channel that the radio is ALWAYS receiving even while transmitting.

So rather than the system infrastructure just ignoring that radio's signal and taking that one repeater out of service until the radio dekeys and gets told to shut up, they have magic radio signals that they can send to a half duplex radio that isn't even listening? That's your conclusion? I'm sure it seems to her like the radio shut up, but do you think for one second that she would actually know? Did she grab a portable, dead key it, then send it a command and actually see the PTT light go out while she was still keying it? Didn't think so. You have to apply some critical thinking skills here.

Manufacturers aren't going to spend money on a duplexer in every radio, just so they can listen to the control channel while they're transmitting. And before you wave your cheap cellphone at us, be advised that they are not full duplex either - they alternate between TX and RX dozens of times per second - surely you've heard the racket that creates in nearby speakers, etc.

 

[bwhite]

Just because the transmit light is still on doesn't mean that the repeater/rebroadcast sytem cannot ignore it. Hey, this is what I got from one of those that do it, the man asked a question about an open mic, this is the answer that those that work dispatch have. Love it or leave it. If y'all have the right answer then go for it. Most of the rest of this thread sounds like speculation of one kind or another.
I'm outta this one, draw your own conclusions.

Frequencies are transparent to Users of the system, not the system.

 

[slicerwizard]

Just because the transmit light is still on doesn't mean that the repeater/rebroadcast sytem cannot ignore it.

Didn't I just say that?

Hey, this is what I got from one of those that do it, the man asked a question about an open mic, this is the answer that those that work dispatch have. Love it or leave it.

Is it reasonable to expect system users to know how the nuts and bolts of it actually work? Do car drivers know how the ECM goes about its duties? Of course not. Like I said, put a bit of critical thinking into this.

If y'all have the right answer then go for it. Most of the rest of this thread sounds like speculation of one kind or another.

There is no speculation when it comes to system radios - they are half duplex - that is not debateable. That eliminates any chance of your "I'm nearly 100% certain trunked radios are always receiving even during a transmission." theory panning out. But, for whatever reason, you seem to be unable to understand what others are telling you.

 

[SLWilson]

Um, It's called a Repeater....

What the hell are you smoking?

A radio CANNOT receive at the same time it is transmitting. At least, not any radios we'd be dealing with. Some technologies like cellphones and the like can TX and RX at the same time, but for the time being, what you are describing is impossible.

Frequencies are not transparent on a trunking system. A trunking system still has a bunch of repeaters on different frequencies - the only difference is that a computer selects the voice repeater to be used for communications.

Your sister might want to re-check her training, because if what you're saying is what she told you, she's sadly mistaken. If a radio is transmitting an open carrier, there is NO WAY for the dispatcher to remotely shut it down. Period.

I'm not sure about the system that you are speaking of, but, on the Ohio MARCS system, a radio ID (by the computer system) can be shut OFF/Zapped/deleted from the system at ANY TIME, transmitting or not. The shut down data is sent to the controller, NOT the portable. Once locked out, the radio is useless until re-activated....

Steve/KB8FAR

 

[bwhite]

Thanx SL.

 

[robbinsj2]

I'm not sure about the system that you are speaking of, but, on the Ohio MARCS system, a radio ID (by the computer system) can be shut OFF/Zapped/deleted from the system at ANY TIME, transmitting or not. The shut down data is sent to the controller, NOT the portable. Once locked out, the radio is useless until re-activated....

Steve/KB8FAR

(emphasis added)

We're talking about two different things here -- trunked system group calls and transmissions from subscriber units. As you describe, the group call can be terminated at any time by instructing the site controller to do so -- it will vacate the talkgroup and allow other subscribers to use the talkgroup over other repeaters/frequencies. (The system should avoid using the frequency pair which the original radio was on until it is fairly certain the original radio has stopped transmitting, otherwise it runs the risk of the original radio stepping on an "approved" radio.)

The authority, be they a dispatcher or radio tech or whatever, does not and can not terminate the group call by shutting down the original subscriber unit -- it will continue transmitting until the PTT switch is released or the time-out period is reached or something breaks (or unbreaks). At that time it will revert back to the control channel and receive the kill signal, if any, or be denied future channel grants when the PTT switch activates again.

Jim

 

[br0adband]

It seems all this could be answered with a simple question:

Since the control channel is never used as a transmitting frequency by any unit and is always receive-only in the units, is it or is it not possible that trunked radios have two tuners in them: one is always receiving the control channel and never transmits, and the other is used for regular transceiver duties?

If the case is that yes, there are two "tuners" in such units, then the answer would be yes, it is possible for a trunked unit to receive commands from the control channel even if the unit were "stuck" in transmit mode, aka hung mic, damaged PTT, etc.

If the case is that no, there aren't two "tuners" in such units, then the answer would be no, it isn't possible for a trunked unit to receive commands from the control channel as the radio is capable of only half-duplex operation: it can receive, or it can transmit, but never both at the exact same time.

Personally, if they didn't design such units to be full-duplex in that respect, I'd have to say it was a pretty stupid move. Such a receive-only circuit would be trivial to construct, barely have any effect on battery life (look how long a simple 900 MHz pager can run off a single AAA battery) and would obviously give the primary control console for the entire trunked system a lot of capabilities, such as disabling a "stuck" transmitter, etc.

Seems hard to believe that in the largest forum on the planet dedicated to radios and two-way communications someone can't just say "No, the damned trunked radios don't have dual tuners and aren't capable of full-duplex operation" with at least some conviction or data to back up the statement.

 

[bwhite]

The long and short of this is that the responders can continute to communicate if dispatch makes certain "moves". The exact manner in which things happen in the background I defer to all of the experts on. As a responder, I don't care what happens on the technical end so long as comms are able to continue unimpeded.

 

[n2mdk]

Easiest solution is the one they use here, if they know which radio it is, call them on their cell phone.

 

[loumaag]

It seems all this could be answered with a simple question:

Since the control channel is never used as a transmitting frequency by any unit and is always receive-only in the units, is it or is it not possible that trunked radios have two tuners in them: one is always receiving the control channel and never transmits, and the other is used for regular transceiver duties?

If the case is that yes, there are two "tuners" in such units, then the answer would be yes, it is possible for a trunked unit to receive commands from the control channel even if the unit were "stuck" in transmit mode, aka hung mic, damaged PTT, etc.

If the case is that no, there aren't two "tuners" in such units, then the answer would be no, it isn't possible for a trunked unit to receive commands from the control channel as the radio is capable of only half-duplex operation: it can receive, or it can transmit, but never both at the exact same time.

Personally, if they didn't design such units to be full-duplex in that respect, I'd have to say it was a pretty stupid move. Such a receive-only circuit would be trivial to construct, barely have any effect on battery life (look how long a simple 900 MHz pager can run off a single AAA battery) and would obviously give the primary control console for the entire trunked system a lot of capabilities, such as disabling a "stuck" transmitter, etc.

Seems hard to believe that in the largest forum on the planet dedicated to radios and two-way communications someone can't just say "No, the damned trunked radios don't have dual tuners and aren't capable of full-duplex operation" with at least some conviction or data to back up the statement.

Well despite the your thought that it was a "pretty stupid move", that is not the way the radios are constructed. Let's get a few points clarified here.

In a trunking system, if a decision is made to inhibit a radio with a stuck mike, when ordered the radio does not get inhibited until it goes into receive mode. Each field radio only has one receiver and one transmitter in use at any one time, each field radio can either receive or it can transmit, it cannot do both at the same time. At the order to inhibit a radio with a stuck mike, the system moves the TG to another repeater pair and shuts down the offending repeater transmitter. When the offending field radio finally goes into receive mode, it is inhibited and the previously isolated repeater pair is put back into the mix. From the view point of every user on the system (except the stuck radio), it seems that the offending radio has been shut off, but in fact it is still holding up a repeater pair because the receiver is still getting the signal, just no other user (including the dispatcher who issued the "kill" order) is aware of it.

On a conventional (either repeater or simplex) system, the hope is that some other radio close by will get the signal and everyone who can hear it will check all the radios they have close to them.

To the technical point of why there are not multiple receivers in a radio, it is not just adding the receiver (which is not the way to keep costs down) but also that a duplexer would have to be included in each radio (just like each repeater has a duplexer (or antennas far apart)) so that the transmitting signal is isolated from the received signal. While technically possible in those bands with set and specific TX/RX separations (like the UHF 5 MHz), a VHF trunking system has no set separation between TX and RX and indeed can be both close or far away in the band and either can be above or below each other. The size of a duplexer (even at 800 MHz) would preclude them from being installed in a hand held, even if some manufacturer saw the need for a receiver being able to be used during a transmit phase, which despite the subject of the this thread does not exist.

Is that enough conviction and backup?

 

[loumaag]

Easiest solution is the one they use here, if they know which radio it is, call them on their cell phone.

That works too! :lol:

 

[hoser147]

Ok , I got a question in ref to the Ohio MARC system, when a panic button is pushed on the portable how is it that the dispatcher can still call over the air to that unit? Ive heard it happen quite a few times? After reading this, I thought that I would find the answer.........Hoser

 

[bassmkenk2508]

Ok , I got a question in ref to the Ohio MARC system, when a panic button is pushed on the portable how is it that the dispatcher can still call over the air to that unit? Ive heard it happen quite a few times? After reading this, I thought that I would find the answer.........Hoser

Wild guess, but it is just probably a short data burst every so and so number of seconds; not a continuous stream of the same alert. My theory.

 

[wlmr]

Ok , I got a question in ref to the Ohio MARC system, when a panic button is pushed on the portable how is it that the dispatcher can still call over the air to that unit? Ive heard it happen quite a few times? After reading this, I thought that I would find the answer.........Hoser

Unfortunately, the field radios can be programmed multiple different ways, emergency alerting styles included. What I may know for one system can be completely different for a system 10 miles from me.

For right now I'm leaving the listing of all the styles and variations for another person to get into.

I've stated the above to explain why it's not a simple question to answer. For the Ohio MARC system, I wouldn't accept as gospel anything but an explanation from BOTH the programmer of the radio AND the system network management person.

You probably better ask this question in the Ohio Forum as a start. Good Luck!

 

[loumaag]

Ok , I got a question in ref to the Ohio MARC system, when a panic button is pushed on the portable how is it that the dispatcher can still call over the air to that unit? Ive heard it happen quite a few times? After reading this, I thought that I would find the answer.........Hoser

The Ohio MARC System is a Motorola Type II system. Emergency TG ID's are the base ID number +2 (unless patched). When the button is pushed on the field radio (remember, the initial transmission is on the CCh input) the TG assigned by the controller is base TG ID + 2. This alerts all radios that can detect the difference that there is an emergency button pushed on a radio...the dispatcher knows what radio pushed the button and all communication is taking place on the base TG ID +2. If your question is how can the radio communicate while the button is pushed, the button push is just like any PTT, the initial transmission is on the CCh input, then the controller assigns a repeater pair and all radios listening to that TG change to the assigned pair; the emergency button does nothing more after the initial transmission on the CCh input. If this confuses you, read the Trunking Basics in the Wiki.

 

[902]

If your system is simplex, there is NO WAY you could hear that from a portable that's been left turned on while someone's fat a$$ is sitting on the microphone.

There may be a remote possibility that you can hear it over a repeater output.

These are "I think I'm doing some good by doing it" policies usually implemented by some political appointee who has no clue how radio works.

Better is to set all time-out timers to 60 seconds and have the end of message send out a unit ID. Then you can see the ID and, if you have the right equipment, remotely kill their radio until it gets repaired.

I am amazed at how many radios are out in the field these days and nobody has the sense to program the )&%($#*^ time-out timer! (I will not let ANYONE on the systems I'm responsible for without first looking at their radio and making sure the TOT is set and not longer than 60 seconds) If you can't say it in 60 seconds or less, you shouldn't be saying it on the radio.