Police radios

Random

Hope this is the right forum!

Can someone tell me how police radios work?

I'm watching shows like Third Watch and you see them telling jokes over the radio to each other ..

Is there a couple of frequencys? Like a "talk to my partner", "talk to dispatch", "talk to everyone"?

Cheers

watty

Depends on kind:
Old UK had handhelds that could talk to each other 150ft or back to base via radio in the car.

Most radios only communicate via base station. The USA has Analogue Trunk radio where channels are dynamically and automatically assigned.

Tetra can communicate via base like as GSM mode or direct to each other. Most new systems are digital with encryption.

The Garda system is so old and insecure and poor coverage they use their own mobiles for anything important.

It's illegal to listen to Garda/Police and more illegal to report what you hear if you hear anything "accidently".

Random

I was watching Third Watch which deals with the NYPD. I'm asking about those ones at the moment but I'm interested in general

"Tetra can communicate via base like as GSM mode or direct to each other."
How's this work? They tune in a specific frequency to chat to each other?

watty

You don't probably tune a frequency. The Tetra handsets work like mobile phones using Digital encryption. I don't know exact details, but I think if the call can't connect via the base it attempts a direct connection.

Even old analogue handsets are channelised. The users would have no idea of frequency.

TV, especially USA TV often has very little connection with reality. Gadgets, radios, PCs etc work in a way to suit viewer expectation or dramatic effect, not based on real world.

Random

"TV, especially USA TV often has very little connection with reality. Gadgets, radios, PCs etc work in a way to suit viewer expectation or dramatic effect, not based on real world."

I accept this and this is mainly why I'm confused. I'm still confused by the whole setup though.

If Bob and Jim are partners using NYPD police radios and Jim goes into the shop. Can Jim radio Bob without the rest of the NYPD hearing?

Is there like a city-wide frequency that everything is on or is each precient on a different frequency and common orders are dispatched separately to each precient?

Thanks

RoundyMooney

I'm sure I don't need to say this folks, but better not to mention specific emergency services frequencies. I don't see a problem with discussion of the technology behind it, in fact I'll probably learn something

Random

RoundyMooney wrote:

I'm sure I don't need to say this folks, but better not to mention specific emergency services frequencies. I don't see a problem with discussion of the technology behind it, in fact I'll probably learn something

That's grand .. call them freqA, freqB, freqC etc.. it's the theory more than anything else.

RoundyMooney

I was always kind of curious about the types of encryption etc. used, not just in this type of application, but others, tbh.

I think I have a lot of reading ahead of me.

watty

ciaranfo wrote:

If Bob and Jim are partners using NYPD police radios and Jim goes into the shop. Can Jim radio Bob without the rest of the NYPD hearing?

Unlikely. If it's repeater based that can't talk to each other at all, or only with everyone hearing if the repeater is duplex. If its Trunk Radio, anyone nearby or if on a repeater everyone could hear. If it was tetra style then they might be able to talk privately but I doubt it. A Digital Mobile phone would be more private . All Digital phones are encrypted.

ciaranfo wrote:

Is there like a city-wide frequency that everything is on or is each precient on a different frequency and common orders are dispatched separately to each precient?

Unlikely, the city is too big and there would be congestion. There might be a city wide emergency calling channel. Certainly in the late 1950s onwards in US you could get a a kind of "civil defence" radio for dedicated emergency broadcasts.

Each precinct would have separate channels of some kind. (Exact nature depending on which generation of radio system they use).

A long chase/pursuit has always been a problem as the police go out of range of their own base and can't contact other bases traditionally. In the UK Digital Tetra Trunked Radio (no relation to USA Trunked Radio which is an analogue selective calling + dynamic channel assignment) is supposed to solve this as it is essentially a private National digital mobile phone network, so anywhere an officer can stay in contact, and the handsets also work like a digital version of a walkie/Talkie able to operate peer to peer up to about 1mile outdoor.

The Garda and Emergency services have been looking for a Tetra/Trunked radio system here for maybe over 15 years.. They are supposed to do something soon. Eircom recently put on approved suppliers list.

watty

Encryption is actually itself very easy and trivial if you use digital voice coding. Typically the raw 64kbps data rate is reduced to about 4kbps to 8kbps by codec (similar to MP3 idea, but the codecs used in phones and VOIP).

Then you can XOR the data with a very long key.

The problem with encyption (for anything) is two fold:
1) Secure distribution of the key*
2) Ensuring that uncyphered data (plain text) can't be obtained relating to any message.

(1) I think needs no explination.

(2) is a more subtle problem and is why the only really secure scheme is a "one time pad".

I'll explain more if anyone interested.


(* this is why CSS, HD / BD, DRM etc all doomed as every PC or consumer device has to have the real key in it, so eventually someone will figure how to recover it, even from firmware/chip)

RoundyMooney

This is all good stuff watty, thanks for sharing it.

Am I right in thinking that all GSM transmissions are encoded in the same way?

In other words, if a journalist or the like could hypothetically possess a single piece of equipment to decrypt a GSM transmission, then the system is not as secure as folk imagine?

I'm aware of course that cell phones went digital, not for reasons of privacy, but for reliability and sound quality.

At least that's what I've assumed.

Oh, apologies to the OP for a slight thread hijack. This is *kind of* along the same limes though

watty

Yes all digital phones, GSM and home cordless are encrypted.

The Digital was for privacy also. Oddly the DECT cordless phones are slightly more secure and 3G is more secure. GSM has been hacked, though it's not as easy as WiFi. You get into trouble having GSM hacking gear though!


DECT vs WiFi VOIP phone handset:
DECT Secure
DECT x 5 battery life
DECT x 3 range
DECT no interference (its own band)
DECT no complicated user settings
DECT base stations with USB to PC (SIP or Skype) or direct Ethernet for built in VOIP via SIP or Skype (depending on Model).

RoundyMooney

Much obliged for the tech info:)

Pataman

watty wrote: »

. You get into trouble having GSM hacking gear though!

Damn, and there I was typing it into ebay.

experimenter

It is illegal to receive or listen to radio traffic which is not meant for you.

I don't understand why anyone should be promoting or explaining how police radios work.

Surely this is against the purpose of this forum.

Maybe a moderator needs to intervene!

experimenter

Read the Charter!!
Some basic rules of thumb are as follows:

It is illegal to pass on to third parties any information received while monitoring transmissions not intended for you, or which you do not have a license to receive.
Reception of said transmissions is in itself illegal (such as Garda, Emergency Services etc.)
The discussion of Emergency Service frequencies, will result in a warning. If a person continues to discuss them, they will get an immediate ban from the forum.
Unlicensed transmissions, or transmissions which exceed permitted power levels, generate unacceptable levels of interference, or fall outside permitted frequencies are also, naturally illegal.

humaxf1

c'mon, lets face it...the radio system used by "law enforcement" in this country is so old and antiquated, PMR446 would be more reliable and readable...plus anyone can listen in. <quak quak hissssssssss> It's a bit like leaving the key in your front door and a big sign, C'MON IN LADS If the powers to be are so paranoid, TETRA should have been rolled out sooner than later, provided it works ;-)

Watty was explaining the mechanics behind it...relax the kaks! All this carry-on about listening in is a bit anal really when you consider the websites which openly stream police/fire/ambulance transmissions in America.

DublinWriter

random wrote: »

Can someone tell me how police radios work?

"Romeo base to Romeo Tango 4"
"Romeo Tango 4, go ahead base"
"Romeo Tango 4, caller reports flying saucer to have landed in St.Anne's park, little green men seen alighting from said veh-i-cal, over"
"Romeo Base, we're on refreshments, over"
"Right so, Romeo Tango 4"

yayamark

watty wrote: »

Yes all digital phones, GSM and home cordless are encrypted.

The Digital was for privacy also. Oddly the DECT cordless phones are slightly more secure and 3G is more secure. GSM has been hacked, though it's not as easy as WiFi. You get into trouble having GSM hacking gear though!

15 years ago we had a cordless and loved it. one day i was messing with it and when i pressed a button i could hear someone elses phone call conversation. It wasnt anyone else on my house. Prob a neighbour.

After my old man heard this he got rid of it as he couldnt trust it.

As for the garda radio- dont think im giving out any state secrets when i say this. The garda system is antiquated and an embarrasment. Tetra is in the pipeline but has gone on for way too long. Tetra works off mobile phone masts so if ur in an area where there is no signal then u cannot transmit:(

T the moment in dublin there is the central command radio which every garda is tuned into and a district radio which every garda within that district is also tuned in.

humaxf1

good one dublinwriter...can't have PC Plod goin' hungry now!

OVARGHHHHHHHHHHHHH!

Random

experimenter wrote: »

It is illegal to receive or listen to radio traffic which is not meant for you.

I don't understand why anyone should be promoting or explaining how police radios work.

Surely this is against the purpose of this forum.

Maybe a moderator needs to intervene!

Please explain how my post contravenes the charter. I'm asking how they work is all ?? I'm not asking to listen in or crack them or discuss what happens on them ??

I'm not asking about speciific frequencys, I'm asking about the general basis of how the system works as I'm confused by TV and movies!

And this thread is old, why you dragged it up to point out such things I don't know ?

PauloMN

random wrote: »

Please explain how my post contravenes the charter.

It doesn't in any way, shape or form - don't worry about it dude. Some people around here will just instinctively go DEFCON 1 as soon as the words "police", "Garda", "army" or "navy" etc. are uttered on this forum, regardless of whether the thread follows the rules or not.

Besides a moderator has already posted on this forum and has already said the thread is fine so long as specifics (like frequencies) are not posted.

Random

That's grand then. Thanks

experimenter

Just some friendly advice, that's all

Police stuff is not my cup of tea, anyway it's boring.

If moderators are happy with police equipment been discussed then that's fine by me.

The sooner Tetra is implemented Country wide the better.

watty

At the moment till they get Tetra they use mobiles for anything "sensitive".

Random

I suppose I'm still a little confused by this whole thing.

Again, without asking for any specific frequencys if I'm a Guard walking down Grafton St with my standard issue radio, who can I speak to?
- all guards in the country
- all guards in the city
- all guards in my district
- all guards within range
- anyone i choose
- my partner
- only a certain control room

Thanks, and again from reading this charter I believe my post remains within it but please correct me if I'm wrong.

yayamark

random wrote: »

I suppose I'm still a little confused by this whole thing.

Again, without asking for any specific frequencys if I'm a Guard walking down Grafton St with my standard issue radio, who can I speak to?
- all guards in the country
- all guards in the city
- all guards in my district
- all guards within range
- anyone i choose
- my partner
- only a certain control room

Thanks, and again from reading this charter I believe my post remains within it but please correct me if I'm wrong.

A garda on the beat on grafton st would be based at pearse st ( i think im no 100%) bu he would have a radio and could talk to Pearse st or the command and control room. It all depends what channel he is on. A handheld would have a limited range so in theory if he had the right channel he could talk to any of the city stations nut prob couldnt talk to the dublin county stations.

watty

Generally they can only talk to their own control room, which might be able to "patch" them elsewhere.

The radios use the Repeater architecture like Taxis or Ambulances. The different services can't communicate directly.

In certain types of emergency situations Wireless Experimenters (Amatuer Radio operators) are useful as they can carry messages between different services and each other. There is no simple method for Marine, Ambulance, Garda, Fire, Mountain Rescue etc to communicate direct with each other and all can easily go out of range of base station or Mobile phone masts.

In Cork some joint exercises that included AREN (the Irish emergency comms group using trained volunteer Wireless Experimenters) have taken place.

In New Orleans the US "Hams" provided vital communications for over a week as the Military took a long time to deploy after Katrina.