Check for open mic .... ??

[KB9NLL]

Around here, all conventional VHF repeaters, hear the dead keyups quite a bit only on police and sheriff, mobile and dispatch. Dispatch girls conversations very interesting in a small county where nothings going on. And by the way even dispatchers with 2 repeater frequencies not counting the fire/ems, with at least two dispatchers carying on a conversation where told on both frequencies about there open mike and still had too get a phone call "ring" "911" "it is!" transmission stops.

I've never heard a cell phone ring when it's a mobile but if it's an H.T. maybe it was fringe getting into the repeater where there's no voice with the transmission. Also have heard dispatcher announce two times on both repeater channels that there was an open mike and it kept going on for sometime yet, so I guess at times they're just hopeing. Over the years I've noticed that the unit number squaks have been more popular.

And last of all I have, although not currently working, a H.T. with crossband repeat built in (a early 1990's model), which even by todays standards is not that big. I know it's not what you guys were arguing about as it's crossband not same band RX/TX but would work/solve the open key problem just the same because not on the same band while in TX would still recieve lets say a turn of or unkey in simplex on the other band. And some of those police/business radios are overpriced anyways and I don't mean the features I mean there ruggedness too.

:evil: Which reminds me of an interesting story when you could still hear cellphones in analog, a friend showed me that you could transmitt live cell conversations on VHF (108-170 +/-) or UHF (440-460 or more). Connecting a VHF repeater to a UHF repeater didn't work to well because it would never stop going back and forth because of the repeater tail at the end of a transmission.:evil:

 

[slicerwizard]

60 seconds is fine for public safety, where the users are generally disciplined. On commercial trunking systems, I wouldn't go past 30 seconds. The dispatchers that have to listen to long winded drivers will appreciate it, as will anyone who's stacked up in the busy queue. And use transmission trunking / zero repeater hang time. A two second hang timer can eat up 25% of your total airtime capacity.

 

[slicerwizard]

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

And that question is "Are (public safety) trunking radios half duplex or full duplex?" And it's already been answered.

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?

No, it's not possible. Don't you think some of the techs here would've noticed by now?

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.

You've ignored the fact that unlike a pager, a two way radio transmits. Even though the need for a duplexer had already been pointed out in this thread, you ignored it. Further, you deride the designers for not adding costly hardware, even though it would not provide any useful functionality. What purpose do you see a dedicated receiver serving? It has already been pointed out that the system infrastructure is more than capable of cleanly dealing with any dead keyed radios, so for what purpose would you have them raise the cost of their subscriber gear, other than to make them less competitive in the marketplace?

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.

I guess someone should've said "There is no speculation when it comes to system radios - they are half duplex - that is not debateable." - but with conviction - and with scanned/uploaded schematics from a dozen trunking-capable radio service manuals?

 

[DaveNF2G]

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)

This makes sense if you don't understand how pagers work, I suppose.

Pagers do not receive continuously. They "strobe" or turn on for very brief times at programmed intervals to listen for their preamble. If the correct preamble is not being transmitted at the time, then the pager goes back to sleep. If a matching preamble is received, then the pager stays on long enough to receive the following tones. If they are not the pager's own tones, then the pager goes back to sleep. If the pager's tones are received, then it "opens up" for the message (voice or digital) that follows - and then goes back to sleep.

A trunking receiver would not work properly if strobing in this fashion.

 

[exkalibur]

Holy jeeze... Plain and simple english. YOU CANNOT TURN OFF A TRANSMITTING RADIO REMOTELY. Period. You cannot do it. It cannot be done. It is impossible. There ARE exceptions to this. IDEN is one exception, as are any other TDMA system. I believe P25 Phase II will allow this capability, but it has not been released as yet. The MARCS system cannot do it. As soon as a unit de-keys, the dispatcher can zap it, but as long as a radio is transmitting, there isn't a thing that can be done to stop it. The dispatcher can stop REPEATING the audio, making it seem like it's stopped transmitting, but he/she cannot actually stop it.

For the record, I am a dispatcher by profession and a radio-tech by hobby/sub-profession. I have hands on experience with SmartNet, SmartZone, IMBE, LTR, EDACS, ProVoice, AEGIS, Conventional and Trunked. I can tell you with absolute conviction (as can slicerwizard) that none of the above systems allow a radio to be turned off while transmitting.

 

[slicerwizard]

YOU CANNOT TURN OFF A TRANSMITTING RADIO REMOTELY. Period. You cannot do it. It cannot be done. It is impossible.

Grasshopper, you lack conviction (as did I, apparently)

 

[DEPUTY11]

Seems to occur more often thru the winter than other times. But know matter when you always get that extra inside conversation.............Hoser

More in the winter on the fire side because the lapel mike gets wet (fighting fire with water) then you come outside into the cold temp and it freezes.