Signal to Noise

The signal to noise is very high in this experiment:

• Two excellent receivers with system temperatures of 65 K (the 100m) and 85 K (the reference antenna).

• The satellite signal is confined to two correlator spectral channels (2*2 KHz).

• The beacon is rated at 9 dBW EIRP. The on-line signal monitor with a 2.5 MHz bandpass showed on boresight a level 30 dB above the system temperature.

  At the edge of the map (1.2 degrees from boresight) the signal to noise in the 4 KHz channel visibility is around 20:1, as figure 3 makes clear.

  Figure 3: The spectrum of a random visibility somewhere near the edge of the beam map (about 1 degree from boresight) that illustrates the high signal-to-noise of the data

  

Figure 4: A ruled surface representation of the calibrated data. Each trace is a scan in elevation; the scans are stacked in azimuth order along the vertical axis. This is the NIGHT observation.

Figure 4 shows the calibrated data (amplitude) in the form of a ruled surface; the horizontal axis is the scan direction (elevation); the scans are stacked in azimuth order. The main features are attributed to :

- The support legs which produce the strong vertical and horizontal sidelobes;

- The central blockage and subreflector which produce the circular sidelobes on the 0.2 degree scale.

The sharp eye will note that the first and last scans were repeated - that is, even at the edges of the map there is little noise in the data. This quality is shown in greater detail in figure 5, which shows a point-by-point comparison of the amplitude and phase for the two copies of the last scan. For reference, the peak (boresight) amplitude is $~\sim$ 10000.

Figure 5: A detailed look at the data quality - the scan most distant from the boresight was repeated. These two figures show the repeatability of the amplitude and the phase.