6.9 SatService-Beacon-Receiver

This page describes the device driver and the device window for the sat-nms LBRX beacon receiver.

Device window pages

The following table shows which device window pages are available with this individual device type. Tool-bar functions not mentioned here are described at the general description of device windows .

• --- The first parameter page displays the receive level and lets you set the basic receive parameters like frequency, bandwidth and input attenuation.
• --- This page lets you configure the C/N measurement mode of the receiver and displays the signal C/N if this mode is active.
• --- This page contains the parameters to configure the frequency tracking facility of the receiver.
• --- The faults page.
• --- The device info page.
• --- The maintenance page. The configuration parameters described below are set at this page.

LO Frequency Calculations

The beacon receiver may store one or more local oscillator frequencies which are used to calculate the L-band frequency at the receiver input from the receive frequency at the antenna. Most beacon receivers support two frequency bands with separate LO frequencies. A model with four frequency bandy and 8-way input switch is also available. With the LO frequencies and frequency band edges setup correctly, the beacon receiver always shows and accepts the input frequency in terms of true receive frequency at the antenna rather than in terms of L-band frequency. Optionally a 22kHz tone may be modulated on the LNB power supply to switch the band.

All LO frequencies are to be specified in MHz. The LO is assumed to be below the input frequency unless the frequency is given as a negative value. In the latter case, the beacon receiver calculates for a LO frequency above the carrier.

Two-band receivers select the frequency band by the 'bandEdge' configuration parameter. Input frequencies below this value get the 'loBandLo' LO frequency applies, frequencies above the edge are calculated to L-band using the 'hiBandLo' LO frequency.

Four-band receivers provide three frequency band edges which divide the input frequency range into four bands. Four separate LO frequencies are applied are applied according to the actual band the selected frequency is within. For compatibility reasons, the lower frequency bands and the band edge in between are controlled by the parameters mentioned above. Two additional band edges and LO frequencies control the upper two frequency bands:

With the 22kHzTone parameter set to AUTO, the 22 kHz tone gets activated if the input frequency is in frequency band 2 or in in band 4.

C/N Measurement Mode

In addition to the normal level measurement, the sat-nms LBRX beacon receiver is able to perform C/N measurements. This is done by measuring the level of the received noise at a frequency other than the receive frequency in regular intervals. Each measured signal level then gets converted to a C/N value by referring it to the noise level value. While the receiver measures the noise level, it freezes the displayed C/N value as well as the analog output voltage for this time.

The behavior of the C/N measurement function is controlled by three operational parameters:

• Parameter Name --- Description

• C/N Noise measurement --- This parameter controls if the receiver shall perform a plain input level measurement or a C/N measurement. The following measurement modes are available:

  • OFF --- The receiver performs a plain level measurement.
  • IN --- The receiver measures the signal / noise ratio. The The C/N measurement page shows the C/N value in dB. and the normalizes C/No value as well.

• Noise Measurement Frequency --- This parameter specifies the frequency at which the receiver shall measure the noise level at a certain interval. Like with the receive frequency, the LO frequency settings made at the Setup page are taken into account also for this frequency value.To get reasonable results with a C/N measurement, you should consider the following:

  1. The receiver does not change the LNB frequency band setting when it switches from the level measurement to the noise measurement. The LNB probably would change it's gain in this case. The noise measurement frequency hence must be in the same frequency band as the receive frequency.
  2. Measuring the noise level at the band edge may falsify the result due to the LNB's band filter. The measured noise level may be too low in this case.
  3. You should verify with a spectrum analyzer, that no signal disturbs the noise measurement at the selected frequency.

• Noise Measurement Interval --- This parameter defines the interval at which the receiver inserts noise measurements in the C/N modes. The time is specified in seconds. 3600 secs being one hour is a suitable setting in most cases.

Frequency Tracking

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 LNC 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:

Configuration parameters

At the maintenance page of the device window there are a couple of configuration parameters which must be set to make the software talk to the receiver.

• parameter --- description

• address --- The IP address of the receiver to control.

• loBandLo --- Enter the LO frequency for the lower frequency band here (MHz), if you want to specify the receive frequency in terms of true RF receive frequency. 'loBandLo' is applied for frequencies below 'bandEdge'. Enter 0 if you want the receive frequency to be displayed as receiver input (L-band) frequency.

• hiBandLo --- Enter the LO frequency for the upper frequency band here (MHz), if you want to specify the receive frequency in terms of true RF receive frequency. 'hiBandLo' is applied for frequencies above 'bandEdge'. Enter 0 if you want the receive frequency to be displayed as receiver input (L-band) frequency.

• loBandLo3 --- This LO frequency ist only available with beacon receivers which support 4 frequency bands. Enter the LO frequency for the frequency band between 'bandEdge2' and 'bandEdge3' here (MHz), if you want to specify the receive frequency in terms of true RF receive frequency. Enter 0 if you want the receive frequency to be displayed as receiver input (L-band) frequency.

• hiBandLo4 --- This LO frequency ist only available with beacon receivers which support 4 frequency bands. Enter the LO frequency for the frequency band above 'bandEdge3' here (MHz), if you want to specify the receive frequency in terms of true RF receive frequency. Enter 0 if you want the receive frequency to be displayed as receiver input (L-band) frequency.

• bandEdge --- Enter the edge between the receive frequency bands here (MHz). The receiver applies the 'loBandLo' LO frequency if the receive frequency is below the edge, the 'hiBandLo' LO frequency if it is above. If the 22kHzTone parameter is set to AUTO, the 22 kHz ist set accordingly.

• bandEdge2 --- This band edge value is only available with beacon receivers which support four frequency bands. Enter the edge between the receive frequency bands 2 and 3 here (MHz). The receiver applies the 'loBandLo' and 'hiBandLo' LO frequencies if the receive frequency is below this edge, the 'loBandLo3' and 'hiBandLo4' LO frequencies if it is above.

• bandEdge3 --- This band edge value is only available with beacon receivers which support four frequency bands. Enter the edge between the upper receive frequency bands 3 and 4 here (MHz). The receiver applies the 'loBandLo3' LO frequency if the receive frequency is below the edge, the 'hiBandLo4' LO frequency if it is above. If the 22kHzTone parameter is set to AUTO, the 22 kHz ist set accordingly.

• lnbVolt --- This parameter controls the LNB supply voltage provided by the receiver at it's input connector. The following settings are available:

  • OFF --- The D/C voltage is completely switched off.
  • 14V --- The LNB supply voltage is 14V
  • 18V --- The LNB supply voltage is 18V
  • AUTO --- The LNB supply voltage is switched on, the voltage depends on the 'Polarization' parameter. The voltage is 14V for vertical polarization, 18V for horizontal polarization.

• 22kHzTone --- This parameter controls the presence of a 22 kHz tone on the LNB supply voltage. The following settings are available:

  • OFF --- The 22 kHz tone is switched OFF.
  • ON --- The 22 kHz tone is switched ON.
  • AUTO --- The receiver automatically enables the 22 kHz tone depending on the receive frequency set. The tone is switched OFF for frequencies below the band edge, switched ON for frequencies above the band edge. The band edge is set with the 'bandEdge' parameter above.

• vOutScale --- This parameter defines the slope of the receiver's voltage output in V/dB. The output voltage has a range of 0 .. 10 V. Setting this parameter to 0.25V/dB lets the analog output cover a dynamic range of 40 dB.

• vOutOffset --- This parameter defines, which input level gives 0V output.

Variables defined by this device driver