4. Front End
The connections between the radiotelescope foci involve three different kinds of signal :
|Local Oscillator : in order to cut down the expenses related to the construction of an high number of independent superheterodyne recevers, a common solution is to share some local oscillators (at least for one conversion). A single local oscillator therefore can serve more receivers through a signal distribution system.|
|IF : the RF signals, once received and converted by the Front End, are sent to the Back End installed in the Control Room, at the antenna base.|
|Reference : 5-MHz H-maser signal, necessary for the local oscillator stability.|
All the signals are distributed via coaxial cable.
The distribution scheme is simplified by the fact that there are only two double-conversion receivers (6 GHz at the Cassegrain focus and 22 GHz at the primary focus). Both use the same local oscillator for the second conversion. Besides the two receiver channels cannot be tuned at different positions inside the RF bandwidth.
The OL signal is distributed by an LO distributor (OLD).
The reference distributor (REFD) and the IF distributor (IFD) are also installed in the Cassegrain focus. The receiver can be chosen from the Control Room using the selector.
Fig. 4.2 : Signal distribution between the foci
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