You probably wouldn’t expect to see someone making astronomical observations during a cloudy day in the center of a dense urban area, but that’s exactly what’s happening at the recent Philadelphia Mini Maker Faire in 2019. Professor James Aguirre of the University of Pennsylvania demonstrated the particularly compact Mini Radio Telescope (MRT) project, built around an old DirecTV satellite dish and a few basic components, giving visitors a view of the sky in a way most have never seen before.
Thanks to the extensive online documentation of the project, anyone with a backup satellite dish and several hundred dollars of maintenance hardware can build their own personal radio telescope capable of observing objects in the sky, regardless of the time of day or weather conditions. Even if you are not interested in peeking into deep space from the comfort of your own home, MRT offers a framework for building an automatic platform for directional antenna with tilt and tilt, which can be used to capture signals from orbital satellites.
C slow collapse of satellite television in the United States these dishes are often free to take and a fairly common sight on the sidewalk comes the day of garbage. Maybe even one (or three) sitting on your own roof as you read this, waiting for a new life in the Netflix Era.
Whether it’s to satisfy your own curiosity or because you want to follow in the footsteps of Professor Aguirre and use it as a STEM contact tool, projects like MRT make it easier than ever to build a functional DIY radio telescope.
Point and shoot
The MRT, and in fact any radio telescope project like this, essentially consists of two separate systems: one that provides the motorized direction of the plate, and the receiver that actually captures the signals. Each system can work independently of the other, but when combined with the appropriate “glue” software, they allow the user to map the sky in radio frequencies.
Obviously, the electronics and mechanical components needed to move the antenna in the sky are not terribly complex. If you want to make things really simple and you’re content with moving on one axis, you can even do it with a barn door tracking device. What really started with the recent explosion of DIY radio telescopes was the RTL-SDR project and the inspired era of cheap software radios (SDRs).
Not surprisingly, MRT also uses an RTL-SDR receiver to process low-noise (LNB) block signals in the vessel. Professor Aguirre says that because they still use the DirecTV LNB stock, the telescope is quite limited in what it can actually “see”. But it is good enough to depict the sun or take satellites into orbit, which is sufficient for the purpose of demonstrating the basic principles of operation of the radio telescope.
To move the satellite dish, MRT uses an Arduino connected to a trio of large easy Sparkfun drivers. They, in turn, are connected to the stepper motors in the antenna stand, which are sufficiently directed to be able to move the plate around without the need for a counterweight. This makes it an excellent candidate for enclosing inside a dome, which would allow observations in all weather conditions.
Both the RTL-SDR and the Arduino are connected to the Raspberry Pi, which runs the telescope software and provides the user interface. The MRT GitHub contains all the various tools and programs created for the project, mostly written in Python, which should provide useful reference, even if you are not interested in duplicating the overall design of the telescope.
Wandering in the sky
When we visited Professor Aguirre, he was trying to use MRT to find the Sun. You’d think it was a simple enough task in the middle of the afternoon, but thanks to a continuous layer of steel-gray clouds hanging low in the October sky, Sol was absolutely nowhere with our meager human senses.
As the dish made its slow robotic pans across the sky, we talked to the professor about the telescope and the various revisions it had gone through over the years. Eventually the display lit up, showing an unusually strong signal, apparently MRT heard something there After a brief examination the professor announced that we had not found the sun; instead, the telescope most likely intersected with a geostationary satellite.
It is this reconnaissance style of discovery that fascinated the visitors of the Mini Radio Telescope. No one expected this hacked together inventing consumer hardware discover a new exoplanet or help solve a long-held mystery of space while sitting in a parking lot in Philadelphia.
But he was more than able to point to objects tens of thousands of miles away, until our own eyes could not even understand where the Sun was. This confirmed in a very real way that there was something there and the students, both young and old, could not help but be fascinated by it.