Thursday 20 September 2012

LBA bandpass spectra

We're now in the midst of some intensive commissioning of KAIRA. Some of us have been working on the High-Band Antenna array and others on the Low-Band Antenna array. Today's report is about this LBA work. One of the things we need to do as part of the commissioning is confirm that all the low-noise amplifiers are generating the correct signal outputs. For each aerial there are two outputs: one for each polarisation. The bandpass spectrum for each of them should look the same (a bandpass spectrum is a plot showing the intensity received as a function of frequency, for the range of frequencies that the system can measure). In the case of a good working antenna, we should see something like this:

The lowest part (0-10 MHz) is filtered out. Then there are various short-wave radio frequency interference. The main part of the band rises up and then tapers off at the top end (going into the FM radio band).

However, we've noted that some channels are a bit weak:

And some channels are quite low across the main part of the band.

Before we can operate the entire LBA array, we will need to resolve these problems and ensure that all components are working correctly. This sort of trouble-shooting and tuning is a standard part of commissioning these sorts of systems.

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