[TheList] Squawking Tones on Police Channel & High Frequency Tone on Channel

Sun Mar 20 10:07:50 AEDT 2022

Hi BJ,

Years ago someone did a write-up about it on here, but basically it's a 
form of SCADA for monitoring sites remotely.  Some sites are often not 
easy to get to and may have access issues such as being helicopter 
access only.  These sites have quite large battery banks, as mains power 
may be flaky.  The SCADA allows for inputs and outputs to be monitored 
remotely.  They are often polled at specific times, which is why 
sometimes you may hear the tones underneath voice comms.  If the 
controller polls and doesn't get a response back then it will retry X 
amount of times (if programmed) then assumes the site is dead, and 
alerts get generated.  A variety of things can be monitored. Often these 
are only 'analog' inputs so you only get very specific details..  You 
could see things like

Battery Bank A is 100/75/50/25% (maybe not even in that much detail)

Generator On/Off

Entry Door OPEN/CLOSED

Alarm ACTIVATED/DEACTIVATED/IN ALARM

SOLAR ON/OFF (IE is there voltage coming into the system on the Solar 
lines)

REPEATER POWER ON/OFF  (some repeaters can have an output that's 
activated when it's in a certain state)  As Daryl mentioned, it would be 
a (probably unreliable) way of determining if a repeater is working or not.

With the NGCC being implemented, a lot of this will eventually become 
redundant as most things like SCADA would be converted to IP based, and 
digital radio is also IP based, meaning a lot of this could be sent over 
a text message over the radio network.  I assume P25, but DMR will 
prioritize voice over messaging.

As for the screeching, lots of factors could be causing that. I-band 
links shouldn't really be used for monitoring as they're only 
point-to-point or point-to-multipoint links meaning you really need to 
be in line of the path for it to be received. I'd recommend use the 
VHF/UHF frequencies.  Once again, with things turning to digital soon, 
they'll probably be redundant with the links will be done over IP.

Cheers,

Richard

On 20/03/2022 11:23 am, Darryl Healy wrote:
> Those tones are something to do with the linking with all the VTGs.
>
> They happen every 4 hours at midnight and so on.
>
> Someone will no doubt give a more technical explanation of them soon.
>
> On Sun, 20 Mar 2022, 11:01 BJ, <bjcuizon151 at gmail.com> wrote:
>
>     Hi all,
>
>     Was in Dunedin recently and tuned in to police comms. Anyone know
>     what those squawking tones on some police channels are? It doesn't
>     sound like fire selcall but more like a really short (~1 sec)
>     burst of what sort of sounds like a part of the old dial-up handshake.
>
>     Also, was listening to firecom and ambo thru the I-band link in
>     Chch and on some link channels there is a really high pitched tone
>     that is present when someone keys up. It can only be heard on a
>     radio with no audio filtering/DSP as my Tait seems to cancel it
>     out. Does anyone have an idea what this is as well?
>
>     Thanks in advance,
>     BJ
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