P r i m a L u c e L a b i S r l
S p i d e r 2 3 0 u s e r m a n u a l
It’s possible to note how the receiver temperature affects in an important way the recorded data (when the tempe-
rature of the receiver increases, the recorded value decreases and vice versa). It’s important to note that even the
ambient temperature influences the recorded data: in fact, during the night (the central part of the graph) in which
the receiver's temperature is stable at 44°C, the value of the radio increases slightly due to the decrease of the
environmental temperature. This phenomenon is evident when the LNB is not equipped with a thermal stabiliza-
tion system.
So when you want to record from very faint objects, you need to pay attention to changes of ambient temperature.
In particular, it is not advisable to record during sunrise or sunset, when the ambient temperature changes signifi-
cantly.
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3)
Tips for radio images
: based on the receiving system settings (described on page 41, setting the required gain as
a function of the object to be recorded), when we point the radio telescope to an area of the sky free of radio sour-
ces, we obtain a numerical value (that, for example, can be of about 8000). When you move the radio telescope
toward a radio source, the value increases due to the signal that arrives from the source itself. Because of the wea-
kness of the signals typical of radio astronomy, it is essential that the background noise remains as constant as
possible. The factors that lead to the variation of the background noise are temperature variations described in the
previous paragraph and variations of the antenna pointing positions. If we set a high gain (eg 10), point the antenna
to the vertical and then move progressively towards the horizon, we can see that at the radio value tends to de-
crease and then increase again.
This phenomenon is due by two main causes. The first is the
atmospheric noise
which is low when pointing the tele-
scope toward the vertical and progressively increases as it moves toward the horizon (because the instrument
"look at" a greater thickness of the atmosphere). The second cause is the
spillover effect
. In practice, due to the par-
ticular geometry of the antenna, the feedhorn “look at” an greater area than the one of parabolic antenna disk. This
means that when the point the antenna to the zenith (vertical position), the feedhorn "look at" radio signal emitted
by the ground and for this reason the radio signal increase (instead of decrease).
The added effect of these two phenomena leads to variation of the signal simply when the antenna of the radio
telescope moves from one point to another one of the sky. Since the direct recording of radio images with the "Ra-
ster Image" feature of RadioUniverse needs to move the antenna to reconstruct the image, this method is good for
intense sources such as the Sun and the Moon but it is not the useful for weak sources (where having a constant
background noise is crucial). For these objects is therefore better to use the transit technique, described on page 51
and then reconstruct the image using the RUviz software (described in the next chapter).
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p a g e
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