4. Front End


4.2 Distribution

The connections between the radiotelescope's foci involve three different kinds of signal :

bullet Local Oscillator : in order to cut down the expenses related to the construction of an high number of independent superheterodyne receivers, a very 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.
bullet 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's base.
bullet 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) and both use the same local oscillator for the second conversion. Besides the two receivers' channels can't be placed in different positions inside the RF bandwidth.

The OL signal is distributed by and OL distributor (OLD).

The reference distributor (REFD) and the IF distributor (IFD) are also installed at the Cassegrain focus. From the control room it is possible to choose the receiver through the selector.


Fig. 4.2 : Signal distribution between the foci

Fig. 4.3 : Distributors : reference signal (on the left) and local oscillator (on the right)

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