Cars 'On local' and picking up other things

[yorky]

Hi, long time reader, first time poster

During my daily drive into work (near city from Kingsley), I often here some local, what seems to be, car to car chatter, no matter what freq I'm on.

It is usually only when I'm close to the city, and going over to channel 34, but sometimes its around when I'm still on channel 21/41 about to cross over.

Basically I get either broken chatter with what seems to be police car to car, saying things like 'GC103 you on local?' etc. And it seems if I'm following a car/bike closely I can hear them loud and clear (except when VKI says something and it 'overruns' what I was listening to). For example at some traffic lights, a bike cop races through on priority with another hot on his heels, and I hear 'Hey Bob slow down mate I'm falling behind'. I knew it was on this 'local' thing cause it sounds slightly different and crackly.

Am I right to to think that its just a low power car to car radio that only works good when they are close by? How am I picking them up when I'm tuning into the normal frequency and how could I tune into them better?

[Steve]

You're kinda on the right right track.

The WA Police Service uses a network of repeaters dotted around the metro area. The radios in the cars transmit on one frequency and receive on another, and the repeaters vice versa.

On police radios there is a switch referred to as 'local' and when it's activated the transmit frequency is changed so that it's the same as the receive frequency. The repeater doesn't get 'triggered' but any vehicles nearby will be able to receive the transmission. For the vehicles to communicate 'car to car' without triggering the repeater, they both have to be transmitting and receiving on the same frequency, so both need to have their 'local' switches activated.

As far as I know (and I'm sure I'll be corrected if I'm wrong) the VKI operators can't hear transmissions conducted on 'local'. To go back to communicating with VKI, the local switch has to be disengaged.

[Guest]

You will find that all traffic cops on operations or bikes running tandem will chat on local. This is even worse in the city with City Support Unit and beats chatting away on local even whilst VKI is giving out urgent jobs via the repeater.

This is a problem that has never been rectified but will once the PMRN digital trunking system is implemented.

[yorky]

Ok, so basically I'm listening to car to car whether I like it or not, which they shouldn't really be talking on since they can't here VKI? heh.

How close do you have to be to a car to hear it clearly? Most of the time it just cuts in and out, I'm using an old Bearcat something or other handheld...

[Guest]

If you are closer to a repeater site you may hear the channel louder than the actual local chat. Reception all depends on location and line-of-sight.

Bearcats are pretty good though you may get alittle bleed-through from commercial areas like Ossy park or O'connor.

By the way, when we use standby channels at VKI we do hear the local chit-chat on the channels because we are listening to the landline input, not the radio repeater output...if that makes sense. We only switch to standby when the repeater output is u/s.

[Steve]

I'm pretty sure the officers can still hear VKI when the switch is set to 'local' - it only changes the 'transmit' frequency, not the 'receive' frequency, so two cars on local can chat away without VKI hearing them, but they can hear VKI should they be being called.

I imagine this could be safety issue for WAPS in the event that a car needs to call in 'urgent' in a fast-unfolding situation and the officer doesn't realise the switch has been left on 'local' - he or she could be yelling into the mic and not being heard at the VKI console.

[vk6hgr]

I imagine this could be safety issue for WAPS in the event that a car needs to call in 'urgent' in a fast-unfolding situation and the officer doesn't realise the switch has been left on 'local' - he or she could be yelling into the mic and not being heard at the VKI console.

With a bit of practice it's fairly easy to hear if a vehicle is coming in via the repeater or on local mode. (that's Motorola's terminology, otherwhere known as repeater talk-around or just plain 'simplex' mode).

On the police repeater, (and almost all UHF CB, amateur and commercial repeaters) there is usually a second or two of blank carrier called the repeater tail. That lets the person who just transmitted know that he's succesfully triggered the repeater. VKI doesn't usually transmit on the repeater, but rather link in to the repeater's transmitter with phone lines, so you usually don't hear a tail after VKI speaks.

I'm still surprised to hear that VKI can hear cars on local mode. That would require VKI to have their phone lines to the repeater sites, plus have an ordinary radio at VKI listening on the repeater channels. I know they do this when the phone lines/microwave links go down, but until now I didn't know it was common practice.

[vk6hgr]

By the way, when we use standby channels at VKI we do hear the local chit-chat on the channels because we are listening to the landline input, not the radio repeater output...

Do you mean the other way around? As in, you hear the local chatter when you're listening to the repeater output when the landline is u/s. That makes more sense to me

Again, it's easy to tell if VKI are in standby mode because they activate the repeater tail just like cars do. I haven't tried this since VKI moved, but from the city it was fairly easy to hear them on the relevant 458Mhz repeater input channel as well.

[Guest]

Gav, yes whatever sounds more logical.

I hate it when a car on channel 8 tells another car (not using local mind you) to take it down one and they talk on channel 7 (Rottnest). We can hear them on the South Metro console, well at least one of them, coz the other one correctly selected Local ON.

Anyway, that's my gripe for the day.

[vk6hgr]

Gav, yes whatever sounds more logical.

I hate it when a car on channel 8 tells another car (not using local mind you) to take it down one and they talk on channel 7 (Rottnest). We can hear them on the South Metro console, well at least one of them, coz the other one correctly selected Local ON.

Anyway, that's my gripe for the day.

Hehe. Why not go /up/ one to ch 9. The IPG isn't there any more

This'll likely be totally elminiated when the police implement their funky new trunking/digital/whatever system. Would be really interesting to see the technical stuff about what the police are going to be doing, after the miserable failure of the Tetra system before it even got off the ground.