The general block diagram below shows the Flexible Converter Assembly including the following units: Downconverter, Upconverter, IF Band-pass Filter and Fixed Frequency Oscillator.
The Downconverter receives an RF-signal at uplink frequency and
performs a frequency conversion of this signal to the selected internal IF band. Bandpass filtering is performed at IF. The downconverted and filtered signal is then upconverted to the applicable downlink frequency by the Upconverter. The amplification according to the requested total gain is distributed to both converters. An LNA can be included in the Downconverter when a receiver function is needed.
The IF filter bandwidth may correspond to the input bandwidth (typically 250 or 500 MHz) in case the complete block of received channels is transferred to the output as a group. The filter may also have a bandwidth corresponding to one channel (typically 36 MHz) in case a channelization of the signal is made at this stage. In this case a set of parallel band-pass filters and parallel Upconverters are used on the payload in correspondence to the number of included channels.
In case of block conversion it is in most cases sufficient to include the synthesizer in the upconverter, the downconverter can use a fixed LO frequency.
The LO signals for the frequency conversion are generated by three
frequency sources. One source is the Fixed Frequency PLO, which
provides a common frequency component for both the Down- and
Upconverter. The other two sources are the frequency synthesizers
located in the Downconverter (if needed) and the Upconverter. These are externally controlled and the frequency is individually selected for each converter.