Nice Try, But It’s Not Aperture Synthesis

Some of the world’s largest radio telescopes are not in fact as physically large as they claim to be, but instead are a group of telescopes spread over a wide area whose outputs are combined to produce a virtual telescope equal in size to the maximum distance between the constituents of the array. Can this be done on the cheap with an array of satellite dishes? It’s possible, but as [saveitforparts] found out when combining a set of Tailgater portable dishes, not simply by linking together the outputs from a bunch of LNBs.

The video below the break still makes for an interesting investigation and the Tailgater units are particularly neat. It prompted us to read up a little on real aperture synthesis, which requires some clever maths and phase measurement for each antenna. Given four somewhat more fancy LNBs with phase-locked local oscillators and an software-defined radio (SDR) for each one then he might be on to something.

If you’re curious about the cyberdeck in the video, you might like to read our coverage of it. And the Tailgater might be a bit small, but you can still make a useful radio telescope from satellite TV parts.

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Your Own 11.2 GHz Radio Telescope

Modern life has its conveniences. Often, those conveniences lead to easier hacks. A great example of that is the rise of satellite television and the impact it has had on amateur radio telescopes. There was a time when building a dish and a suitable low noise amplifier was a big deal. Now they are commodity parts you can get anywhere.

The antenna in use is a 1.2-meter prime focus dish. Some TV dishes use an offset feed, but that makes it harder to aim for use in a radio telescope. In addition to off-the-shelf antenna and RF components, an AirSpy software-defined radio picks up the frequency-shifted output from the antenna. There is more about the software side of the build in a follow-up post. We liked that this was a pretty meaty example of using GNU Radio.

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Welcome To The Slow Death Of Satellite TV In America

During an earnings call on November 29th, CEO of AT&T Communications John Donovan effectively signed the death warrant for satellite television in the United States. Just three years after spending $67 billion purchasing the nations’s largest satellite TV provider, DirecTV, he made a comment which left little doubt about the telecom giant’s plan for the service’s roughly 20 million subscribers: “We’ve launched our last satellite.

The news might come as a surprise if you’re a DirecTV customer, but the writing has been on the wall for years. When the deal that brought DirectTV into the AT&T family was inked, they didn’t hide the fact that the actual satellite content delivery infrastructure was the least of their concerns. What they really wanted was the installed userbase of millions of subscribers, as well as the lucrative content deals that DirecTV had already made. The plan was always to ween DirecTV customers off of their satellite dishes, the only question was how long it would take and ultimately what technology they would end up using.

Now that John Donovan has made it clear their fleet of satellites won’t be getting refreshed going forward, the clock has officially started ticking. It won’t happen this year, or even the year after that. But eventually each one of the satellites currently beaming DirecTV’s content down to Earth will cease to function, and with each silent bird, satellite television (at least in the United States) will inch closer to becoming history.

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