Radiotelescope Recording Devices
To be of any value, the output of a radiotelescope must be recorded.
For the simple radio telescope described here, what we want is a record
of how strong the signal is over time. If we are using drift scan
observations, we can relate the time a particular value of signal strength
was recorded to where in the sky our antenna was pointed. The result is
often called a strip chart. Below is a great example of a strip chart
from the web pages of the radio observatory at the University
of Indianapolis in Indiana. This is a chart of the radio source,
Taurus A, taken as the rotation of the Earth moved the beam of their antenna
across this region in the constellation Taurus.
In the old days, most strip charts were made on mechanical strip
chart recorders. These devices had a pen which was deflected (in response
to an applied voltage) across a moving continous sheet of paper. These
devices are seldom used anymore and most data is collected and displayed
on a computer. In order to make the transition from a continuously varying
analog voltage (the output of the radiotelescope) to digital information
which the computer can process a special device is required called an analog
to digital converter. These devices come in many forms. You can find out
more about them here at our website. Special software graphs the
data received from the analog to digital converter and it can be printed
if the need arises.
Drift scans are nice, but what if you want to make a map of the skys radio
emissions? Well, all you have to do is plot drift scans of the sky
at a series of elevations separated by somewhat less than the angular beamwidth
of your antenna. If you live in the northern hemisphere, you could
begin by pointing at an elevation close to the north celestial pole near
Polaris, and running your telescope for 24 hours. If you had a beamwidth
of say 10 degrees, you would then lower the elevation by about five to
seven degrees and making a strip chart for that elevation. You would
continue the process until the beam was point a bit above your horizon
and then combine the data files to make a 2 dimensional map of the sky.
In reality, there is quite a bit more to it than this. Calibrations half
to be maintained and other factors like the interference and radio noise
from the ground considered. Still, you get the idea.
If you intend to record sporadic events such as Jupiter's noise storms
or meteor reflections with your radiotelescope, you can use PC's sound
card as a recording resource. Sound cards are great for recording sounds
in these specialized cases, but remember, the output of the generalized
radiotelescope in our example is not sound, but a slowly varying voltage
which corresponds to the amount of energy or antenna is picking up from
the region of sky towards which it is pointed.
| BEGINNERS | JUPITER
| SOLAR | PULSARS
| PROJECTS | FAQ
| BOOKS | SOFTWARE
| SUPPORT | ORDERING
| LINKS | CONTACT