Sierra 200 owner manual Methodology for System-wide Audio Level Setting

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.

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