RDS technology
TMC (or Traffic Message Channel) is an inaudible radio signal which is transmitted on the FM band by means of RDS technology. TMC provides information on traffic-jams, road works, mobile speed cameras and driving conditions. This information is spread via several radio channels, and is shown on the display of most of nowadays (RDS compatible) headunits. TMC is also used by a lot of navigational systems. If a traffic jam should occur on a calulated route, the device can then re-calculate an alternative route and mention this to it's user.The use of TMC information in navigational systems usually requires a separate accessory, since only few PND's have a built-in TMC antenna. Eg. the popular TomTom GO range also hasn't got one of these antenna's built-in. TomTom has announced an optional TMC module for the newest models, but that piece of hardware won't be released until this fall. Tests are being performed with the TomTom TMC module as you read this.
Antennas
Garmin has had TMC antennas in their assortment for some time now. They had the GTM10 and GTM11, the first Garmin TMC antennas. These connect to a lot of Garmin navigational system models, like the Nüvi range and the Streetpilot range.These first generation TMC antennas required the user to connect them to the car stereo antenna, which was then used to pull the TMC signal from the airwaves. The PND then processed the received traffic info. Clearly, this wasn't the most handy setup.
The GTM11 TMC model has been discontinued by now. The new GTM12 model (see photo) will most likely be a lot more popular with Garmin users. All they have to do with this model, is connect it to the PND's mini-USB connector, attach it to the windshield with two small suction cups, and then the GTM12 is ready for use. Yes, this model operates completely independent from the car stereo. The GTM12 is suited for the following Garmin PND's: Nüvi 300, Nüvi 350, Nüvi 310, Nüvi 360, Streetpilot c340, Streetpilot 2720, Streetpilot 2820, Streetpilot 7200, Streetpilot 7500 and the Zümo 550. It costs a little less than 100¤ (68 £), and it's available in all shops that sell Garmin hardware.
Besides this newly released GTM12, Garmin is also expected to release the brand new GTM21. This antenna also has a 12 volts adapter, which means that it not only receives TMC signals for the PND unit, it can also be used to charge it. This TMC module is meant especially for the StreetPilot c510, the StreetPilot c530 and the StreetPilot c550. The Zümo 550 is the only PND which can use both the GTM12 and the GTM21.
