5.3 C/N Measurement
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 --- Remote Command**Description
- C/N Noise measurement --- mmodThis 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. The Readings page shows the input level in dBm.
- C/N --- The receiver measures the signal / noise ratio. The Readings page shows the C/N in dB.
- C/N0 --- Like the C/N mode, but the receiver normalizes the C/N value to 1 Hz measurement bandwidth. The Readings page shows the C/N0 in dBHz.
.ts Noise Measurement FrequencycnmfThis 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:
- 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.
- 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.
- You should verify with a spectrum analyzer, that no signal disturbs the noise measurement at the selected frequency.
- Noise Measurement Interval --- cnmiThis 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.