Medium frequency

Abstract: A first radio station receives a message in a first frequency band from a second radio station and passes the message to a third radio station in a second frequency band, where the width of the first frequency band differs from the width of the second frequency band. The modulation of the data in the message is maintained unchanged and the first radio station is not required to perform decoding of the message.

Abstract: The invention relates to a method for generating frequencies in a direct conversion transceiver of a radio communication system operating in two different frequency bands. In this method a first frequency band comprises a first transmission frequency band and a first reception frequency band, and a second frequency band comprises a second transmission frequency band and a second reception frequency band. The frequencies are Generated by using one frequency synthesizer (12) and a reference oscillator (14), which generates an essentially constant mixing frequency (L04).

Abstract: Short antennas have again attracted broadcaster attention. These kinds of antennas have been used since the 1920s. At that time it was the logical antenna as a new application of this service after more than twenty years of telegraphic transmissions. Telegraphic transmissions were the most important radio communication service at that time, and because of the long range needed the lowest frequencies as possible were employed. For this reason very short antennas were used even if their size was enormous. Top loaded monopoles were very popular and this technique was employed for broadcast use before the vertical transmitting mast exhaustive study was carried on in the thirties. Nowadays a short antenna would be useful for low power applications and specially to be mounted on building tops. Of course this kind of antennas is not intended to replace the optimum monopoles or vertical dipole where maximum efficiency, maximum gain and antifading properties were achieved after exhaustive studies and after long experience theoretically and practically achieved. CFAs, short monopoles, short dipoles and short folded monopoles have been analyzed from the theoretical and practical point of view in order to choose the simplest and most efficient. model to fulfill downtown stringent requirements.

Abstract: A radio communications system operational within the medium frequency range for underground mine communications, coupling MF carrier signals into existing conductive channels extending to within the mine and devices within the mine and coupled to the conductive channel for receiving the MF carrier signals and communicating with portable and mobile transceivers operational within the MF frequency range and in the common seam mode.