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Methodology for System-wide Audio Level Setting
Buffered audio from each of up to 8 receivers is distributed on the backplane. Each
radio control board selects from 0 to 8 of the receive signals to mix and send to that
particular transmitter. Each receiver and transmitter level can be adjusted with internal
digital potentiometers.
The control system routes a standard internal signal level of 1v peak-to-peak for full
system deviation from all receivers to all transmitters. Receive input signals to the RCB
should to be between a minimum of 250 mv p/p to a maximum of 4v p/p. The buffered
output to each transmitter will be between 0 v to a maximum of 4v p/p. If for some
reason you need more gain in either the receiver or transmitter buffers, you can change
the values of the resistors on corresponding op amps or add audio squelch boards that
provide a wide range of audio buffering and audio signal processing options. The
opamps used in the RCB are low voltage devices that will handle a maximum of 4 v p/p.
The following procedure is used to set all audio levels. It is assumed that you have
either two service monitors or one which can generate and receive on different
frequencies at the same time. One service monitor is used as a signal generator to drive
the receivers and the other service monitor is used to receive the transmitted signals.
For illustration, assume you have a system with one repeater on port 0 and 4 link radios
on ports 1 through 4.
The audio level set pots can be controlled in four ways:
- Directly setting a pot value through DTMF on a radio port
- Interactively setting a pot value through DTMF on a radio port
- Using a dumb terminal program connected to the serial port of the CPU board
- Using the SRS CONFIG program to interactively set all pot values.
While any of these techniques would work fine, the BEST method is #4. In this
approach you have full control to adjust all digital pots from the graphic user interface.
Once set, you can also store the configuration on your PC. This methodology explains
how to sest the audio level in a conventional 5 Khz FM radio system. Regardless of the
method of setting each pot, here is the sequence of steps you would perform to set all
levels properly…
Step 1 – Set the Port 0 Rx level.
Set your service monitor to generate a signal that your repeater receiver
frequency.
Generate a 1KHz tone with a RF deviation of 2.5 KHz on the receivers frequency.
Probe the DB-15 Con_2 Aux I/O socket Pin 10 with an oscilloscope.