(Newbie needs help) QAS Infrastructure

[chanjyj]

Pardon me. I know most here are well versed and will find the below questions rather irritating (I knew I was, when people used to ask me "what is the range of this walkie talkie"!), but if anyone could take the time to clear up my misconceptions it would be much appreciated.

Some info on my radio background. I am not a hardcore scanner enthusiast. My experience is in ham radio and small-scale commercial radio. That said, I used my ham radios to operate like a scanner but they are definitely not built for anything beyond simple repeater operation (aka no trunking, no digital, nothing). I should be able to grasp the technicalities.

I recently shifted to Brisbane to complete my 2nd Bachelors, and brought along with me 1 ham radio, 2 commercial radios and one inconspicuous Diamond CR77 2.15dBi (144/430MHz) antenna.

Ok, now on to my questions:

1. I have been scanning the QAS frequencies for a while. I live in the CBD, and thus my reception is not fantastic, and highly directional. I noticed however, that there are some frequencies that TX the same content. Eg:
412.8500/118.8 and 413.1750/118.8.

This led me to conclude they were simulcasts.

2. Further research on radioreference.com, brisbanescan.com and this website indicates that:
412.8500/***.* is a repeater located on CONSTITUTION HILL
412.8500/***.* is a repeater located on RAZORBACK
413.1750/***.* is a repeater located on CALOUNDRA
413.1750/***.* is a repeater located on MINERAL HOUSE

I looked up the locations on Google Maps and realised they were quite far apart. The only plausible reason I could come up with is that the entire state of Queensland has a repeater within a certain coverage zone, where they will all receive any and every TX made (Gold Coast will hear Gympie) etc.

This doesn't make much sense for me as the system will be choked up with radio traffic and nothing will get through. In addition Channels 1-9 are clearly delineated as voting groups..

3. Hopefully you can see where my misconceptions are coming from. So what sort of system is the QAS using?
- Voting groups might indicate a trunked system - is the QAS trunked?
- 2 simultaneous transmissions is verified, but is this evident of a simulcast?
- 2 simultaneous transmissions might be evident of a UHF link back to the command centre from a voting panel (receiver site) rather than a leased telephone line. In this case, there is no simulcast.

Could anyone clarify for me how the infrastructure is? Is it an off-the-shelf system like Motorola Type 2 SmartZone, generic MPT-1327 trunking or a mixture of everything?

Thank you in advance.

Regards
Joel

[Phil]

Joel,

each channel has a different CTCSS, for the QAS i have learnt that they reuse the frequency 3 times, for example

412.8500 as stated is located at both Mt Coot-tha and Razorback Range however they are not linked in any way, the QAS use Radio Linking from each site to create a vote group, QAS are using Conventional non trunking all you need to do is program in the Receive on for where you want and away you go

[chanjyj]

Thanks for the quick reply Phil, appreciate it.

I get the part about frequency being re-used with different CTCSS. A rather efficient and cost effective method to go about things.

Regarding vote groups, I understand the concept of a vote group(s) but not how it is applied here. My understanding is from your post:
QAS mobile/portable TX >> several receivers >> voting panel >> dispatcher RX
then
QAS dispatcher TX >> QAS mobile/portable RX

Am I correct here? Because if so I shouldn't be hearing the paramedics on the ground TX-ing. Or are the sites are linked via RF (instead of wire-line connections)? In that case I would be hearing the RF links, which does explain the situation.

The fun for me is in enjoying knowing what I'm listening to

[alinco21]

Hi Joel,
voting group apply to the menu on the QAS radio. you really don't need to understand the working of it if you just intent to listen to the frequencies.

413.275 - Metro North
412.850 - Metro South
412.575 - Bne Patient Transport Services
414.8125 - Ipswich
all come off Mt Cooth-tha

413.125 - Mt Cotton - Beenleigh.
to hear the QAS unit or hand held you will need to be listing on the input reperater freq that they are Tx.

Paul.

[Phil]

iv found i hear both off Mt Cotton never heard a one way convo yet

[chanjyj]

Hi Joel,
voting group apply to the menu on the QAS radio. you really don't need to understand the working of it if you just intent to listen to the frequencies.

....

u will need to be listing on the input reperater freq that they are Tx.

Paul.

Hi Paul, I sure know how to listen. But for me the fun of it is in deciphering the system (which I've kind of failed at so far). It's much more interesting for me when I know who (what?) I am listening too rather than just the voice comms.

I used to program radios for my company (commercial radios), had a strong HAM background (amateur radios) , was in the Air Force and finally worked for a while with the Singapore Auxilliary Police Force. I guess it's ingrained in me to find out the hows and whys. I remember once sitting at a shopping mall for 1 month trying for figure out the odd repeater offsets, and hit pay dirt when I traced the 2 receivers and 1 transmitter back to the physcial repeater buried in the basement of the shopping mall. Talk about persistence.. my girlfriend was not amused

iv found i hear both off Mt Cotton never heard a one way convo yet

This is one thing I am trying very hard to understand - why you are able to hear two-way conversations off a single frequency. It's getting on my nerves.
1. If it's the dispatcher you're hearing = the site is a remote TX site linked to the central station.
2. If it's the dispatcher and paramedic you're hearing = the site is a repeater.

There is only 1 plausible reason I can think off - the remote site is only a repeater with a remote link back to the dispatcher's TX panel.

Comint has sent me a PM informing me that vote comparators don't even come into the picture. A voting group in Queensland is simply a scan group. But what he states does support the theory that the remote site is indeed a repeater - but here lies the question how 1 repeater is able to receive a puny 4W signal from a Motorola GP339 when the area covered is so large.

[chanjyj]

Golly. To say I'm confused is an understatement. But what's the fun if you have nothing to figure out

Phil, could you elaborate on your statement "each repeater is a standalone and are all linked via RF Linking"?
Standalone as in a received signal is not re-broadcast over the other repeaters (simulcast) while linked meaning the received signal is linked to the dispatcher?

I'm trying to visualise how such a system works.

[Phil]

Each site is linked and simulcast


Sent from my iPhone using Tapatalk

[alinco21]

They are linked the QAS units just pick the closest repeater to Tx on or the voting group self picks and Tx on it.

not much more than that.



[quote="brisbanescan"]Each site is linked and simulcast


Sent from my iPhone using Tapatalk[/quote]

[chanjyj]

Things are starting to fall into place now, thanks for all the help so far. One of the false assumptions I made (silly!) was the Motorola GP339 was just a 2/5 Selcall version of the MDC-1200 GP338. Major fallacy - it adds voting in as well, which explains some things.

My brain is a tad busted now after spending the entire day working through this, so I'll look at it over the next few days. Pretty conventional system after all, I was thinking of something esoteric.

[rapps_101]

See below - I took this from a recent QAS training manual. It shows the repeaters linked for Region 5 (Brisbane) Central voting group

Edit: it doesnt display very well in the forum post and cuts of CH112 at the Airport

[chanjyj]

Thank you so much rapps_101! Off topic, is the manual for the ambulance crew or the radio techs?

[rapps_101]

Manual for the civvy radio operators that work in their call/dispatch centre at Kedron

[311alpha]

[quote="rapps_101"]See below - I took this from a recent QAS training manual.

At the risk of asking a stupid question, Where do you get a copy? Is it restricted to QAS only?

[alinco21]

possilby works there, perhaps. But not for long perhaps if it is restricted as said.

[rapps_101]

Nope, not employed by DCS.

It's hardly restricted, it shows channel numbers and vague repeater locations.

I work with someone that was previously employed at QAS

[alinco21]

no really that hard to work out anyway, via the ACMA site. just takes a bit of time.

[rapps_101]

Exactly right.. It's even easier if you use the Spench RF maps.. Nonetheless, I was just trying to offer some insight to the radio network to the OP. if it was restricted, they wouldn't let an ex employee keep the training folder