Interference-free zone at Westerbork
The delicate radio telescopes of Westerbork are interesting just as they are. But the invisible border that protects their reception is quite unique.
I knew about these telescopes all my life. When I was 14 I spent a whole long trip from Switzerland reading about their precise construction and the amazing technique of interferometry.

I first saw briefly them in 2000; 26 years later. And I saw them again again in 2002. Then I had more time to explore them and their surroundings.

They are fully operational, and if you sit quiet enough you'll hear the purring of the motors that continuously adjust their position.

I always wonder what they're looking at. It's obvious that they're aimed at something, but during the day the target is invisible. It would be nice to climb all over this structure. It is so inviting.
Access is limited to research staff. There are a lot of fences and gates and "do not enter" signs. And although it would be easy to climb a fence I didn't do it, out of respect for science. And there are camera's too, although I doubt that they are for security. I suspect that they are for safety control, when the telescopes move on their rails.
The telescopes are still behind the trees (on the horizon) but the signs that are scattered over the landscape announce their presence.

You are not allowed to use motor vehicles and mobile phones in an area of 2.5 km around the telescopes. This is meant to reduce interference from terrestrial radio-sources.

I immediately switched off my GSM, but in practice it's a rule that's not really enforceable: "Sir, may I check your phone please?"

Some distance from the moveable telescopes there is a long row of fixed telescopes. These are not mounted on rails, but still they can be pointed to any direction in the sky. From time to time they shift their orientation as they follow their invisible target in the sky.

Here there are no obvious cameras. The whole field is visible from inside the building that houses the control-center. A few people were sitting on the garden chairs on the lawn. But the sign said: "No visitors, no guided tours."

And even in the woods you will find the signs that forbid all unwanted radio signals. I like it.
Border crossings
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