I sometimes passivley scan through Private Mobile Radio (PMR446) channels and am surprised at how many stations I can hear.
Chances are, you’ve bought some PMR446 licence-free radios and have charged them up, picked a channel and started using them. The issue here is that ANYONE in range can listen in. For example, I have a couple of schools locally, a sports centre and some sort of builder/property maintenance company in my immediate vicinity.
I know this because I’ve picked up their transmissions this morning.
There is a setting on PMR446 radios, which may be more easily set through programming software, that provides what is called Continuous Tone-coded Squelch System (CTCSS) or Digital Coded Squelch (DCS).
CTCSS works by adding a special tone to your voice when you speak. Only radios set to hear that same tone will pick up the message. It’s like having a key to unlock the conversation, so even if others are using the same frequency, they won’t hear you unless they have the same key.
DCS works similarly, but instead of a tone, it uses a digital code to make sure only radios with the same code can listen in.
So, unless your transceiver is configured with the same CTCSS/DCS tone as the PMR user, their transmission will be blocked.
This is not foolproof, obviously; if someone tries each CTCSS or DCS setting, eventually they will be able to pick up your transmissions, but it is a layer of protection which it seems a lot of users may be unaware of.
If you want to know more about this, or how to set CTCSS/DCS on your handhelds, let me know, I’ll be happy to help.
