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The new cryoPAF (cryogenically cooled Phased Array Feed) receiver
is currently at the Parkes Observatory for testing and a trial fit-out
in the focus cabin.
The first tests were conducted
on the ground, with the cryoPAF looking up at the sky.
A convenient practical unit for characterising a receiver is the receiver antenna temperature, which
is not the physical temperature as might be measured with a thermometer,
but rather is the temperature of a matched resistor whose thermally generated power per unit frequency
equals that produced by the receiver.
The receiver temperature can be measured by placing a "hot" load in front of the receiver and
recording the detector output voltage, and then repeating the process with a "cold" load.
Often the hot load is at the ambient temperature and the cold load can simply be the sky.
The image above shows the "hot box" that was lowered over the cryoPAF to measure the hot load.
The spiky foam, like that seen lining anechoic chambers, ensures no stray radiation enters
the receiver and that is is only responding to the ambient thermal thermal temperature of
the load. (Image credit: John Sarkissian)
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