Description of Radiomodem MD400 (MD300, MD160)


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2. Description of Radiomodem MD400 (MD300, MD160)

2.1. Radio part

The architecture of MD400, MD300 and MD160 radio modems resolves most of the requirements placed on a top quality user friendly radio modem with a very short switching time between receiving and transmitting. Frequency synthesis enables operation on any random channel from a given frequency band. The operation of the radio data transceiver module is controlled and diagnosed by the micro-controller. The receiving part of the radio modem works with double mixing. Concentrated selectivity is divided between both intermediate frequency levels. The first filter carries out basic channel pre-selection up until attenuation which ensures the linear function of the following second mixer and intermediate frequency amplifier. The second filter of concentrated selectivity has an attenuation characteristic necessary for channel selection in the used channel spacing of 25 kHz. Logic circuits, switching stations between modes of receiving and transmitting, have high noise immunity and switch respective blocks sequentially. This minimises most transient parasite states and optimises bandwidth during switching. Station block modes are logically tied and switching of the station to transmitting mode is tied to the frequency synthetiser lock, the internal temperature of the radio transceiver module and the value of the supply voltage.

2.2. Modem part

he control microcomputer has 4 MB of FLASH memory and 16 MB of RAM memory available. The battery, real time backup supply, detector of supply voltage failure and watch dog circuits belong amongst the other circuits of this block. If there is a supply voltage failure the fact is recorded into memory with the respective time data thanks to the charge stored in electrolytic capacitors. The user therefore has information available about the time and duration of possible faults caused by power failures. It is possible to connect equipment with signalling rates up to 115.2 kbit/s to the modem via the RS232 data interface. RS232 interface converters are protected against overvoltage with TRANSIL elements. A lithium battery is used for backing up in the modem part.


Owing to the use of lithium batteries in the modem part it is not recommended to store them for a period of longer than 2 years.

2.3. Supplying

The radiomodem is supplied by the DC current 13.8 V. The consumption in the quiet state is from 350 to 500 mA according to module used, the consumption at transmitting is up to 2 A. (high-performance radio modems of type P – up to 5 A) The modem can be set in the SLEEP mode when the consumption drops down to 2.5 mA. The return in the active mode can be done by the signal inputting on the serial port or after a preset time.

2.4. Radio Modem Assembly

Radio modems MD400 (MD300, MD160) are special devices which require skilled assembly. All supplied equipment is assembled by RACOM at the user’s site. For subsequent maintenance RACOM specially trains the user’s skilled staff and as an additional aid provides them with Operating regulations for radio data networks and MORSE Firmware – Documentation.

High-performance radio modems of type P (see serial code) need to be installed in a manner which takes into consideration their high demand for heat dissipation, i.e. the rear side of the modem needs to lie tightly against the mounting plate, as it also serves as a heat sink.


CAUTION! Danger of explosion upon replacing the incorrect type of battery. Follow the manufacturers instructions for handling used batteries

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