S-COM 7K, Руководство пользователя, Страница: 365 / 400

Installation
C-7
After you have completed the repeater receiver audio interfacing, check the
audio level at Pin #1 of U37A. It should be 700mV RMS (2V p-p) when the
receiver is fed a fully- deviated 1KHz sine wave tone from a service monitor.
Repeater Transmitter Audio
Your transmitter will require audio from the controller. Connect the audio input
of the transmitter to Pin #14 of J2 (the female DB25S connector).
To get a better idea of how to interface your particular transmitter’s audio input
to the controller, let’s examine the controller’s repeater transmitter audio output
circuit. This circuit consists of two op amps and a number of discrete parts. The
first op amp, U34D, is an audio summer (mixer) with two inputs from the
crosspoint switch. Typically, one input carries repeat audio and the other
carries the CW ID tones; however, the controller’s software can switch a
number of sources to these mixed inputs. The second op amp, U34A, is the
transmitter audio driver. The output impedance of the driver is 600 Ω . A 50K
pot, R104, is connected between the two op amps and serves as the master
gain pot for the transmitter audio.
The controller’s driving capability depends upon the load impedance presented
by the transmitter’s audio input.
•
If the controller is driving a load of 10K Ω or greater, the output level can be
adjusted from 200mV RMS (0.5V p-p) to 2V RMS (5.6V p-p).
•
If the controller is driving a 600 Ω load, the output level can be adjusted from
100mV RMS (0.3 p-p) to 1V RMS (2.8V p-p).
Note:
In most 600 Ω systems, nominal level is 0dBm, or 775mV RMS. This
corresponds to the 80% clockwise position of R104.
If your transmitter’s audio input is much more sensitive than the level figures
given above, or if you must drive the microphone input, the gain of the
transmitter audio driver op amp should be reduced.
•
This is accomplished by cutting an input resistor, R75 (27K). Clip one lead
and lift the resistor. This modification reduces all audio sent to the
transmitter.
•
If the controller is driving a load of 10K Ω or greater, the output level can be
adjusted form 40mV RMS (113mV p-p) to 400mV RMS (1.1V p-p).
•
If the controller is driving a 600 Ω load, the output level can be adjusted from
20mV RMS (56mV p-p) to 200mV RMS (565mV p-p).
Note:
Although it is always a good idea to use shielded cable between the
controller’s audio connections and the repeater’s audio connections, it is
especially important to do so when driving sensitive mic inputs in transmitters.