FDNY Radio System Question

[firemann57]

On most radio systems a call from the field starts like this:
"Engine 123 to Central." and the Dispatcher answers that call.

But on the FDNY system it often seems that I don't hear the field unit initiate the conversation.  is it because of MDT or some other means the dispatcher knows the field unit is calling or do I just not hear the first part of the conversation because of the mixer or some other feature of the system?

Bill E. In Chi-town

 

[memory master]

It's the mixer. 2 different frequencies. I'm sure that one of our dispatcher members will give you the whole lowdown.

 

[tbendick]

The mixer is controlled manually by the dispatcher. It is kept in the off position until someone calls.

Mixer is off
Engine x to Manhattan (you don't hear this)
Mixer turned on
Manhattan to engine x (you hear this)
Conversation continues
Mixer turned back off

 

[nfd2004]

Just a little "Blast from the Past" here.

Back in I guess the early 70s, as I tuned in the FDNY on my crystal controlled scanner, I was able to pick up the mobile units of the FDNY, 60 miles away, but I couldn't pick up any mobile units right from my own local area. I didn't understand that and I asked my father how come that happens. He was pretty much into electronics at the time, so he had told me how he read about "repeater systems". Nobody else had them as far as we knew. So needless to say, he was as impressed as I was.

Now several decades later, those other cities all use a repeater system. If you can pick up the main channel, you'll hear the rigs too. But it was the FDNY, way before these other places had any idea of any system like this.

I guess the "mixer off" is just another way of saying; "The repeater is off". If you have that frequency programmed in the area where they are transmitting from you can pick it up. And like the main channels, each Boro has their own "mixer off frequency".

 

[firemann57]

Tom,
Thanks for the explanation. Of course, that begs another question: why do they turn the mixer (repeater) off until called?
As always, I appreciate the insights from the guys in the know.
Bill E. In Chi-town

 

[FDNY150]

Because if we keep the mixer on, it's like an open carrier. Gets annoying after a while, ya know??

 

[Bulldog]

Because if we keep the mixer on, it's like an open carrier. Gets annoying after a while, ya know??

That's Kind of a Strange System, standard repeater systems don't act like an open carrier, they come up with a microphone is keyed.  You would think that would be a lot easier than that inspectors having to remember to turn the mixer on and off.  They could still have the option to turn off for confidential conversations.

 

[tbendick]

Its not a repeater system at all. Has all the parts of a repeater , looks like a repeater to you and I. However the brains behind it are not a repeater controller. Anyone that has ever worked a dispatch center can think of it like a console patch between the Rx and TX radios

 

[Bulldog]

Its not a repeater system at all. Has all the parts of a repeater , looks like a repeater to you and I. However the brains behind it are not a repeater controller. Anyone that has ever worked a dispatch center can think of it like a console patch between the Rx and TX radios

Well, if it's actually a patch it makes sense why they have a switch to turn it on and off but you said a patch is nothing but a repeater in disguise!  Seems like a good easily automate it and make things much simpler.

 

[fdhistorian]

Its not a repeater system at all. Has all the parts of a repeater , looks like a repeater to you and I. However the brains behind it are not a repeater controller. Anyone that has ever worked a dispatch center can think of it like a console patch between the Rx and TX radios

It is a 'full duplex' system and it is configured without an automatic repeater so that both sides can talk and listen to each other at the same.  This allows the possibility of either side passing important information even when the other is talking.  We accept and use this concept daily with telephones.  You can't interrupt a long winded talker on a repeater because they won't hear you, but you can do it on a phone. 

 

[firemann57]

OK, thanks for the detailed explanation.  I have noticed the open carrier (which I also did not understand) until the dispatcher turns off the switch.  Now I know why!

As I think about it, in 50 years of Public Safety radio use and monitoring, the FDNY system may be the first real duplex system I have ever heard.

Bill E.

 

[fdhistorian]

FDNY is probably the only US FD that uses the power of full duplex communications.  It is ideal when the number of field units and the number of incidents are both large.  It keeps the communications exclusively between the dispatcher and the field units.  Notice how there is no tactical 'cross talk' from unit to unit on these channels.

 

[manhattan]

Very true, but I think that additional factors here are radio discipline, which includes good control of the net by the Dispatchers,  and professionalism by all concerned.  Any system can be knocked off its feet if those two elements are missing or compromised.

 

[fdhistorian]

Professionalism says it all.

 

[firemann57]

...and minimizes the effects of:
- the "open mic / stuck key" problem,
- passer-bys messing with an apparatus radio,
- a nit wit hacking into the system with a cloned radio.
Bill E.

 

[guitarman314]

...and minimizes the effects of:
- the "open mic / stuck key" problem,
- passer-bys messing with an apparatus radio,
- a nit wit hacking into the system with a cloned radio.
Bill E.

  AMEN!

 

[3511]

Great info and discussion. Always noticed that FDNY units did not talk to eachother. Military units could by pass net control and go to each other. FDNY dispatchers need this limitation to effect control.

 

[baileyjeff]

Why is the mexer always kept off?

 

[Bulldog]

Why is the mexer always kept off?

The answer to this question is answered in several posts at the end of the 1st page of this thread.

 

[manhattan]

Great info and discussion. Always noticed that FDNY units did not talk to eachother. Military units could by pass net control and go to each other. FDNY dispatchers need this limitation to effect control.

Actually, they do talk to each other on the fireground tactical channels.  Here again it shows how professionalism and discipline come into play as there is almost never any playing with the radio system.