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Mar 24th, 2010 at 5:54pm
The options file configures your receiver to tune to a particular nominal frequency.
The actual incoming carrier frequency is always slightly different from this, due to LNB local oscillator stability, satellite local oscillator stability and doppler shift due to satellite movement.
When the initial carrier acquisition occurs, your receiver centre frequency drifts to match the incoming carrier and then the AFC (automatic frequency control) loop locks up and the demodulator then starts to work out the actual symbol rate (symbol rate lock) and eventually which are 1s and which are 0s in the data stream (FEC, data stream and framing lock).
The options file specifies the acquisition range over which the receiver will sweep around the nominal frequency, while trying to find the wanted carrier. A narrow acquisition range is not compatible with low stability DRO LNBs, which may be off frequency by +/-1 MHz or more. A very wide acquisition range is not suitable for narrow carriers, as the receiver may accidentally lock to an unwanted, but similar, nearby carrier. The acquisition range must be wide enough to embrace the full daily frequency error range (mainly due to LNB temperature)
Best regards, Eric.
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