Differences between TNC-X and the MT-TT4
The TNC-X, when combined with a uDigi board, is a TNC (terminal Node controller) Together, these products cost $116.00. These are roughly comparable in function to the Byonics TT4, which sells for $65.00 in kit form, and $75.00 assembled. The TNC-X has a nice metal case, the TT4 is sold as a board level product
The MT-TT4 combines a radio transceiver operating on 144.390, with the TT4 controller, packaged in a small plastic enclosure. This can function as a tracker, a digipeater, an APRS weather station, and other functions, including sending multiple channels of radio telemetry. The MT-TT4 allows you to plug in a PS/2 keyboard for sending APRS messages, and for changing the configuration of the tracker/digi. The MT-TT4 has an output to allow you to hook up an external LCD display, which is handy to have when you set up your digi, since it will display the received signals from other stations.
The TNC-x uses a modem chip to decode 1200 baud data-the only format it can receive. The MT-TT4 (and the TT4) use software decoding , so it can process any type of signal ( different baud rates, TouchTones, etc) and it can transmit pretty much anything that Byonics can write for it.
The TNC-X is a nice unit, but its just an encoder/decoder for APRS, adding the uDigi board makes it a digipeater, but you need to have it connected to a transceiver to make it work as a digipeater.
Either of these two techniques, (TNC-X, plus Digi module, plus radio) or the MT-TT4 ( self contained unit, or two parts if you want the 10 Watt amplifier) are good approaches to building a digi without having to dedicate a PC to the job. The MT-TT4 eliminates most of the difficulties you might encounter with trying to mate a radio to a TNC ( which can be a pain with either the regular TT4 or the TNC-X) and all you have to do is set up the configuration on a PC, add power and an antenna, and you are on the air.
Allen
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