Newbie question about PL and MDT

[lzeroual]

what exactly is a PL for example if a frequency is 155.650 and The PL is 136.5.

do i need to do something special in the scanner do have to ad the PL in my channel list ???

also what exactly is a MDT frequency ????

 

[bneilson]

PL is short for Private Line and is basically a sub audible tone that is emitted by a radio to open the squelch of another radio. The concept is such that multiple people can use one Freq. and not hear each other. This is very common on the business DOT freqs. Most public safety systems will use it as well. You dont need to enter it into your scanner, but it may help if you are having trouble hearing things. Without the PL tone, you will here everything as opposed to just the stuff that is using the tone.

As far as MDTs they run on everything form 400 MHz up into the 900 MHz range. Unfortunately I do believe it is not against federal law to monitor now though...

 

[lzeroual]

MDT ???

What does excatly MDT MEan ???

Mobile date terminal ???? is it what the cops use to transmit data ???

 

[scannerfreak]

Mobile Data Terminal

They are in-car computers used to access records information, send messages to dispatchers and other MDT Users, and they can also be used to file reports...

When a dispatcher dispatches a unit to a call, they will also send the call to the units MDT..Which has all the info on that call, caller name, address, type of call. etc...

 

[lzeroual]

MDT

so i guess if you pick up an MDT frequency you will hear like a noise \
like a modem does ???

 

[crayon]

Re: MDT

so i guess if you pick up an MDT frequency you will hear like a noise \ like a modem does ???

Sort of.
Visit this website for a recording of a common 19.2k MDT transmission:

http://www.kb9ukd.com/digital/rd-lap19200.wav

There are other recordings on the site that will help you as well to ID transmissions.

 

[PJH]

Monitoring/decoding MDT information is a grey area. I think there are federal laws that actually say its a no-no to do so, just like cell phones etc.

In our part of the world, most MDT's are interfaced with a commerical cell network(CDPD), so its a mute point anyways. Some of the larger cities who have had their own MDT's for years will have their own non-cell based network.

As a FYI, CDPD is going away shortly. I believe CT and MA's PD will be operating on a GSM based network, but I haven't received all the info from the state yet. The new modems are coming in Januaruy.