Handbook

Denver Channelised CE
User/Maintenance Handbook
Handbook Nō.-50-063708HBKM Issue No:-2
Date:-03/11/2003
Page:-
43 of 51
5.5 UHF Simplex Channel Shelf 60-063706
5.5.1 Simplex Controller PCB (13-002811)
5.5.1.1 Description
The Simplex controller logic PCB monitors the receiver squelch output for a signal change
and activates the supply switching for either the uplink or down link path accordingly. In
normal operation, the low level Rx path is activated, any the associated Tx path is switched
off. When a signal is detected by the Rx Squelch module, the Rx squelch output goes low
(0v), which triggers the controller logic PCB. The PCB mutes the power supply to the
opposite path Rx LNA’s and switches on the power to the output power stage. In order to
prevent the power stage noise blocking the opposite path’s low level receiver, the power
amplifier is normally muted.
5.5.2 ALC Attenuator Module (17-001201)
5.5.2.1 Description
The AFL Automatic Gain Control system consists of two units, a detector/amplifier and an
attenuator. The detector/amplifier unit is inserted in the RF path on the output of the power
amplifier, and the attenuator is situated in the RF path between the 1st and 2nd stages of
amplification. However, in this case only the attenuator is employed as part of the simplex
control system
The attenuator comprises a 50Ω P.I.N diode, voltage-variable attenuator with a range of 3 to
30dB. The attenuation is controlled by a DC voltage which is derived in this instance from
the simplex controller board.
5.5.3 Simplex Squelch Controller PCB (17-002802)
5.5.3.1 Description
The difference in signal levels between the up and downlink paths means that the channel
modules would latch onto any signal in the band rather than a signal at the desired channel
frequency. This is achieved, in part, to having the simplex controller apply maximum
attenuation (via the AGC attenuator unit) to the downlink path, when the uplink is active.
All other modules in this shelf are described elsewhere in this document.