The sat-nms LBRX beacon receiver using it's non-coherent receiver design, does not automatically follow an input signal drifting in frequency like a PLL receiver would do. To let the receiver compensate effects like an LNB frequency drift due to temperature or Doppler frequency shift, a frequency tracking algorithm has been implemented in the receiver.
With frequency tracking enabled, the receiver tunes the receive frequency a small amount up and down at certain intervals. Such a search step takes less than one second, while the frequency is detuned, the level reading and the analog output of the receiver stays frozen.
The step size used for a frequency search step depends in the measurement bandwidth, the receiver automatically selects the appropriate step size. Receiving a C/W signal, the receiver software expects a signal degradation of 1..3 dB when the frequency has been tuned up or down. The receiver evaluates the signal center frequency by comparing the measured level, at the old frequency f , at f+d and f-d to the known shape of the filter.
The behavior of the frequency track facility is controlled by three operational parameters:
| Parameter Name | Remote Command | Description |
|---|---|---|
| Frequency Tracking | ftrk | This parameter switches the the frequency tracking facility of the receiver ON or OFF. Please note, that switching off the frequency tracking does not reset the frequency offset which is applied by the frequency tracking. To reset the offset, set the receiver's frequency setting. |
| Frequency Tracking Interval | ftri | This parameter sets the interval on which the frequency tracking procedure operates. The value is in seconds. Recommended settings are 15 seconds to tune the receiver quickly to a frequency you do not know precisely. For normal operation a frequency tracking interval of one hour (3600 secs) is recommended. |
| Frequency Tracking width | ftrw | With this setting you limit the frequency offset the frequency tracking procedure may apply to the nominal frequency. The frequency tracking never tunes the receiver to a frequency outside the specified range, a frequency track fault is generated if the tracked frequency reaches the limit. |