Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why do some radio towers blink?

jeffgeerling.com

Post reply on HN
Print view View original

21–30 of 131 posts

Re: Why do some radio towers blink?

#21

Post by scblock »

jrockway wrote: post #19
anyfoo wrote: post #17

Earlier quoted context omitted.

If they don't sync to a common clock source, they won't stay in sync for long. Probably not even for a few minutes or so. You'd get the same phenomenon that you see when operating turn signals in traffic. They seem to weave "in and out" of sync. The frequency at which that happens is the beat frequency, i.e. the difference between the two blinking frequencies.

There's got to be some rubidium frequency standard that's a drop-in replacement for a 555 timer ;)

GNSS (GPS) is the typical standard used.

Re: Why do some radio towers blink?

#22

Post by floatrock »

scblock wrote: post #13
rollulus wrote: post #7

Slightly off topic: typically, lights of neighboring towers blink asynchronously. But sometimes they are synchronized. Very satisfying. Anyone knows how this works? My best guess is e.g. DCF77. Thoughts?

When it's on purpose it's typically done through GPS driven clocks. This is how wind farms manage it, where all towers are required to blink together.

Yeah, I've seen it with windfarms. Always wondered why do they need to blink at the same time. The scale of the blink is pretty jarring at night (but also awe-some, in the same way any big enough infrastructure project inspires a kind of awe).

Wind farms have a certain amount of nimbyism because they "spoil the natural landscape." (So do regular farms -- nothing natural about grain silos or row crops, but that's a side topic...) Anyways, having that many towers blink in unison across that big a landscape is a weird effect when you first see it. I think there's an argument that if they blinked independently it would feel more natural in a way.

But since the blinking is all FAA requirements, I assume it's to help identify all the individual towers from the air. I suppose if they were all blinking independently, it would be a predator-trying-to-focus-on-a-single-zebra-in-the-herd problem, except in this case the predator is a pilot trying not to crash into a turbine.

Sure would emit more subtle 'part of the landscape' vibes though.

(Which I guess is exactly what you don't want when you're flying above them. Sigh.)

Re: Why do some radio towers blink?

#23

Post by askvictor »

rollulus wrote: post #7

Slightly off topic: typically, lights of neighboring towers blink asynchronously. But sometimes they are synchronized. Very satisfying. Anyone knows how this works? My best guess is e.g. DCF77. Thoughts?

My observation is not that they are sometimes synchronised, but some subset of the towers are synchronised (this was my observation in Melbourne AU). Upon asking reddit, it appears that it is the FAA-preferred option that all lights are synchronised: https://www.faa.gov/documentLibrary/media/Advisory_Circular/...

Re: Why do some radio towers blink?

#24

Post by evertedsphere »

floatrock wrote: post #22
scblock wrote: post #13

Earlier quoted context omitted.

When it's on purpose it's typically done through GPS driven clocks. This is how wind farms manage it, where all towers are required to blink together.

Yeah, I've seen it with windfarms. Always wondered why do they need to blink at the same time. The scale of the blink is pretty jarring at night (but also awe-some, in the same way any big enough infrastructure project inspires a kind of awe). Wind farms have a certain amount of nimbyism because they "spoil the natural landscape." (So do regular farms -- nothing natural about grain silos or row crops, but that's a si…

> Always wondered why do they need to blink at the same time.

presumably this makes it more striking, and thus easier to notice and avoid

Re: Why do some radio towers blink?

#25

Post by scblock »

floatrock wrote: post #22
scblock wrote: post #13

Earlier quoted context omitted.

When it's on purpose it's typically done through GPS driven clocks. This is how wind farms manage it, where all towers are required to blink together.

Yeah, I've seen it with windfarms. Always wondered why do they need to blink at the same time. The scale of the blink is pretty jarring at night (but also awe-some, in the same way any big enough infrastructure project inspires a kind of awe). Wind farms have a certain amount of nimbyism because they "spoil the natural landscape." (So do regular farms -- nothing natural about grain silos or row crops, but that's a si…

It's so pilots see the entire wind farm as a single entity and can interpret what they see and understand the extent of the wind farm easily. There is a pretty good study you can read on this:

https://www.airporttech.tc.faa.gov/DesktopModules/EasyDNNNew...

As to community impact, radar-activated lighting is an approach that is being used in places this is a concern. It allows the lights to remain off unless there is a plane within the envelope that requires the lights to activate. It's expensive though.

Re: Why do some radio towers blink?

#26

Post by skinwill »

I worked at a television station years back that was designed in such a way that the lights going up the tower were powered by the separate phases of three phase AC with the one at the top powered from all three combined. This was pretty normal but what the engineer had done was rotate them at every level so that if a phase was dropped you could count the lights and quickly see from a distance that the power wasn't right. 4 lights was good, 3 meant you dropped a phase, and so on. I thought it was a pretty clever way of keeping light on all sides of the tower while being able to tell from a distance that a phase was out.

Re: Why do some radio towers blink?

#28

Post by butlike »

skinwill wrote: post #26

I worked at a television station years back that was designed in such a way that the lights going up the tower were powered by the separate phases of three phase AC with the one at the top powered from all three combined. This was pretty normal but what the engineer had done was rotate them at every level so that if a phase was dropped you could count the lights and quickly see from a distance that the power wasn't r…

Fascinating

Re: Why do some radio towers blink?

#29

Post by Johnny555 »

scblock wrote: post #3

FAA details the marking and lighting requirements here: https://www.faa.gov/regulations_policies/advisory_circulars/...

One interesting fact I learned in a different discussion is that when LED lights are used for obstruction lighting, the FAA has standards that require infrared emitters to make them visible to night vision goggles, since unlike incandescent bulbs, some LED's can be invisible to NVG's.

https://www.faa.gov/sites/faa.gov/files/airports/engineering...

Post reply on HN