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.

Mapping

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.