Comment by ajford | Hacker News Reader

Comment by ajford | Hacker News Reader

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Green Bank and the local town is a really cool place. It's a shame to see that some people are giving up on the attitude that's helped protect the telescope's ability to perform amazing science.

My undergrad work used some data from that telescope, and I've spent a few different weeks out on site at various times.

The article mentions the use of diesel vehicles, but neglects to mention that the presence of control electronics is making it harder and harder for the facility to use modern diesel vehicles as the radios, ECUs, and in many newer vehicles even the ignition system radiates vast (relatively speaking) amounts of unwanted radio. When I was there a decade ago, they were lamenting the loss of a couple late-60's or 70's model diesel trucks (see this short article from autoblog with images https://www.autoblog.com/2014/04/24/national-radio-astronomy...) that were just beyond further repair at that point.

I was friends with some summer interns out at GBT during late 2000s, and they mentioned how the student housing at the time didn't have computers, as it was in direct line-of-site of the telescope and the building wasn't shielded well enough. So they had a notepad on the fridge which was for "consulting the oracle" the next day. If the group had a question that required research/google, it was jotted down and they took turns looking it up the next day and emailing the group with the collected answers.

On another tangent, I've heard from some people out that way they're starting to run into some problems with people claiming to be "Electro-sensitive" seeking refuge in the town, then causing hell with the local population and in some cases even trying to blame the observatory for "transmitting". (note this claim is all hear-say from friends who worked there or know people who worked there)

> ...and in some cases even trying to blame the observatory for "transmitting"

But doesn't it transmit?

Most radio receivers use the superheterodyne principle, where the idea is to combine the signal from the antenna with another one that is generated by the receiver. As a result radio receivers tend to emit signals close to the frequency they are tuned for.

Note that I don't believe that electrosensitivity is anything but psychological. I am just curious to know if there is at least some truth in that statement.

Green Bank Observatory does not intentionally transmit, and any leakage would hardly exist for long, since the whole point is to listen to extremely weak signals.

However, a radio telescope differs from your usual radio receiver in that the stages are often separated by vast distances. I'm unfamiliar with the exact signal chain used in GBT, but I do have plenty of experience with a similar scale telescope, the Arecibo Radio Observatory.

A radio telescope will go to huge lengths to reduce the system noise of the receiving elements, including cryogenically cooling the receiver and first few stages of amplification. These signals will then often be brought down within a shielded enclosure (often within a shielded receiver room) and shifted into their intermediate frequency (IF) stage with a highly pure local oscillator (LO) signal and brought back down to the control/electronics building.

In the case of both GBT and Arecibo, that IF is brought down as modulated light over fiber optics, meaning that there is no RFI leakage possible on the transport. And at both, the conversion back to IF is done within a shielded room. At GBT, if I remember correctly, that room is within the Jansky Lab, which was designed as a shielded building.

All of this is to say that it's very unlikely that there is any signal at all transmitting out of the telescope system in any way.

Just noting that a superheterodyne receiver doesn't transmit on purpose, it's just mostly that it generates an internal frequency reference some multiple of the target frequency that has a tendency to leak out. For a normal radio this isn't too relevant as the signal isn't particularly strong or in a frequency range where it'll mess with anything.

As a bit of an aside: The intermediate frequency leaking is how the police can detect if you're using a radar detector (for avoiding tickets from speed cameras for instance). Of course listening to a faint signal like that is best done with a superheterodyne receiver, so there are radar detectors that detect if the police are using a radar detector detector nearby, which is then in turn of course called a radar detector detector detector.

wikipedia has some more info: https://en.wikipedia.org/wiki/Radar_detector#Counter_technol...

Old diesel vehicles are horrific polluters.

It sounds like this telescope needs to be relocated to the Moon. There just aren't many places on this planet left where you can avoid EMI/RFI, and where anyone would want to live.

The energy required to put anything on the Moon is immense. Meanwhile, pollution from rockets is not well understood yet: https://www.scientificamerican.com/article/how-much-air-poll.... Meanwhile, a telescope on the moon would be pointing at the sun (a very bright radio source, mostly due to proximity) for long periods at a stretch.

TLDR: the moon probably isn’t an ideal location.

This unscientific and non data backed opinion simply isn't contributing towards meaningful dialogue.

But what about the post you're replying to?

Ultimately the telescope will have to find a way to cope with the modern EM environment. Moving off-planet does have some incredible advantages if the budget is there. Failing that, modern signal processing can work miracles, compared to what was available when the Green Bank site was commissioned. I assure you that forcing everyone in the vicinity to drive older diesel vehicles is not the right solution, whatever the problems may be.

In the 1990s, only the vehicles used on the observatory property were antique diesels. The people in the surrounding area drove normal cars and pickups. I imagine it is still the same.

This is exactly the case. There's a small perimeter zone around the sensitive telescopes where unshielded/unapproved vehicles are prohibited, unless otherwise scheduled for some reason. This small area is the only place where these antique diesels are in use. They are in no way forcing the people in the nearby towns to use diesels or anything of the sort.

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