Specifications

Installation

Table 2.8: ASI Output Connector

Item Specification

Connector type: BNC 75 Ω socket

Connector designation: ASI OUT 1

ASI OUT 2

ASI OUT 3

ASI OUT 4

Pin-outs: Centre Video Signal

Shield Ground/Chassis

2.7 Configuring the Demodulator for Best Performance

2.7.1 Demodulator Acquisition Tips

This section is a useful checklist for debugging the Demodulator acquisition process, with some

tips for getting the best performance.

To debug the Demodulator acquisition process:

1. Check the input connection. The L-Band connection must be connected to the correct

input and the correct input selected under software control. Input 1 is closest to the Ethernet

connector.

2. Check the LNB control signals. The 22 kHz switching tone is switched off by default.

3. Check the L-Band frequency.

4. Check the Demodulator configuration. The spectrum sense may be true or inverted. The

symbol rate, alpha, modulation and coding must be correctly configured. The frequency

acquisition range must be correctly configured – this is described below.

The frequency acquisition range is dependant upon symbol rate, the use of FFT assistance and

use of the frequency sweep.

As a basic rule without FFT assistance the frequency acquisition range can be assumed to be 2%

of symbol rate for QPSK and 1% for 8PSK.

If Spectral Analysis (FFT assistance) is enabled – then the acquisition range for all modulation

types can be assumed to be 10% of symbol rate. For example at 64 ksymbol acquisition would

be +/- 7 kHz. To increase the acquisition range it is possible to set a frequency sweep using the

sweep range and step size settings.

Therefore, to increase the 64 kSymbol acquisition range to +/-30 kHz the sweep range could be

set to 30,000 Hz and the sweep step size set to 12 kHz.

Note

It is not recommended to use the Spectral Analysis (FFT assisted acquisition) above

3MSymbols as this will significantly slow signal acquisition.

The command which enables or disables FFT assistance is set to auto by default; in this case

the FFT is only enabled when the bit rate is less than 1.5 Mbps.

SBD75e Series Demodulator Installation and Operation Manual

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