4.7
RECEIVER FUNCTIONS
There are several user configurable features in the 9785. Two fundamental configuration requirements
include line termination (for impedance matching) and setting the receive frequencies. Adjusting for
the actual receive level is covered in paragraph 4.8.3. If any external carrier level meter is to be
installed, the system must be configured for the type of meter connected. The Alarm Output Relay has
programmable pick-up and drop-out times. Consult RFL if you have any questions regarding the
proper configuration of the 9785.
4.7.1
LINE TERMINATION
The 9785 receiver section can be configured to terminate the incoming line or not. Note that the input
of the RF Interface Module is a high impedance input. The termination and protection circuits are
located on the Line I/O assembly at the rear of the unit. To change the termination setting, the Line
I/O Module must be removed from the chassis and the jumper selected for “50
Ω
” “75
Ω
” or “OUT”. If
the receive sections of several chassis are interconnected, only one of them should be terminated. Note
that the termination impedance is only specified up to one watt maximum. See Section 19 for more
information.
NOTE
In two-wire operation, Rx tied to Tx (W3 and W5 shorted on I/O), the local transmitter
terminates the receiver and the Line I/O terminal jumper must be set to “OUT”.
4.7.2
RECEIVE FREQUENCIES
The receive center frequency must be programmed into the Receiver Downshifter module which is
used to translate the received signal down to the desired 4 kHz baseband frequency. This is
accomplished using switches SW1 and SW2. See paragraph 11.4.1 for more information.
The bandwidth of the received signal determines which Receiver Detector module is required in the
system:
A 500 Hz bandwidth system requires one 500 Hz BW Receiver Detector module (assembly no.
106515-1).
A 1000 Hz bandwidth system requires one 1000 Hz BW Receiver Detector module (assembly no.
106515-2).
A 1500 Hz bandwidth system requires one 1500 Hz BW Receiver Detector module (assembly no.
106515-3).
RFL 9785
RFL Electronics Inc.
March 24, 2008
4-9
(973) 334-3100