A 70cm Wide-band Transceiver Concept

This article presents a description of a 70cm wideband transceiver for duplex operation. The modules are designed for operation in a 200 kHz wide duplex channel, freely selectable from 430-440 MHz with a 100 kHz channel spacing. First prototypes were introduced on the international Packet Radio Symposium in April 1997. Some minor changes resulting
A 70cm Wide-band Transceiver Concept - schematic

from further experience were added to the text since then. Narrow-band packet radio net access frequencies with 25kHz channel spacing for operation with either 1k2 Baud AFSK or 9k6 Baud FSK are state-of-the-art and standard for over 15 years now. They are common in wide areas of Europe. These transmission speeds are sufficient for connecting local BBS systems, taking part in packet radio conversation groups or accessing DX clusters. There are, however, new emerging applications requiring higher transmission speeds. These requirements ask for higher speeds of one order of magnitude compared to the standard 9k6 Baud operation. Examples for such applications are new BBS systes with HTML graphical user interfaces, digital voice transmission or image transmission in real-time following the ISDN standard. Inter-node links following those requirements are currently being set up. High-speed user accesses to the packet radio network are still missing. In Germany, there is currently a single 70cm packet radio channel assigned for user accesses with a bandwidth of 200kHz. This channel has experimental status and the assignment of further channels cannot be foreseen. Therefore, the user TRX is designed as a single channel version without any user interface for changing the frequency. The frequency however, should be changeable through re-programming. The transceiver must be adaptable to be used either as part of a digipeater or a user...

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