Microwave relay system R-901; manufactured by Standard Telephon Radio, Zurich.

In 1954, Standard Telephon Radio AG in Zurich (STR) got a development order for a frequency-modulated 400 MHz microwave communications station.

Despite successful testing, the station was not ordered in series, probably because the priority was to acquire RB stations to accomplish the microwave relay network of the army (RSA).

• Principle: transceiver (microwave relay station)
• Operation modes: FM (F3)
• Frequency range: 325 - 400 MHz, 100 channels
• Transmission power: FM (F3) 20 watts
• Transmission capacity: 6 speech channels

Based on a development order placed in 1954, STR Zurich developed the frequency-modulated microwave communications station R-901, which operated in the 400 MHz range; development was ready for series production in the 1950s.

Despite successful troop trials in 1957, the station was finally not procured and the signalmen had to continue to work with the TLD stations for a few more years until the R-902 station was ready to be introduced in 1967.

The tube-equipped R-901 station consisted of a number of heavy cases (three each for the transmitter and receiver sections) and a guyed antenna mast, which carried the transmitting and receiving antennas with their four dipoles. It operates with motor tuning in the 325 - 400 MHz range, the transmitter has an output of 20 watts and the receiver is a single conversion superhet with an IF of 42 MHz.

In 1967/9, the compact 8 MHz station R-902 was introduced instead of the then obsolete R-901.

• Richtstrahl bei den Übermittlungstruppen, W. Bäschlin, p 31 / 146