Receivers on the 100m telescope are operated in the frequency range 400 MHz to 86 GHz with instantaneous bandwidths from a few MHz up to 2 GHz. Such input frequencies are translated by one or more oscillators into the IF range. Signals lying in the range 50 - 250 MHz constitute to the Narrow Band IF and this is transmitted over coaxial cables from the focus cabins to the receiver rooms. The frequency dependent attenuation of these cables is compensated by correction filters having an opposite characteristic. The 1024 channel autocorrelator, the pulsar signal dedisperser, the narrow band polarimeters and the MK III VLBI Terminal all accept this Narrow Band IF. The VLBA Terminal, the 8192 channel autocorrelator and the 16 channel pulsar unit however use 500 to 1000 MHz as input frequency range.
We will successively modify most of the existing receivers to the 500 - 1000 IF. As the number of high quality coaxial cables between cabins and the control room is limited, we will use IF-multiplexers in the telescope to switch between receivers.
In preparation for spectroscopy with a bandwidth greater than 500 MHz we have started to install an optical fibre IF-transmission system.
Receivers with bandwidths greater than 200 MHz have within the receiver box broadband detectors or a broadband polarimeter for continuum observations. This frequency range is called accordingly "Broadband IF". It is not, for technical reasons, the same for all systems. It can range from 800 MHz to 1300 MHz, or from 1 - 2 GHz, or 2 - 4 GHz. The output signals from the broadband continuum devices are transmitted to the receiver rooms as digital signals (V/F conversion following detection).