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Why do some radio towers blink?

jeffgeerling.com

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Re: Why do some radio towers blink?

#81

Post by wolrah »

Johnny555 wrote: post #29
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...

That is one of those wonderful facts that's both interesting and in hindsight completely obvious.

Re: Why do some radio towers blink?

#82

Post by genter »

xenadu02 wrote: post #36
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…

This is best practice for anyone who uses three phase power. A machine shop should connect 1/3 of their lights to each phase so it is immediately obvious if a phase gets dropped. Lots of equipment will suffer on two of three phases but with lower performance or even damage.

I was told that you want lights on all 3 phases so that you can see spinning things spin. If the lights are on single phase, they will dim 120 times a second, and the strobe effect can cause spinning things to appear stationary. With 3 phase, at least 1/3 of the lights are lit all the time.

Re: Why do some radio towers blink?

#83

Post by buildsjets »

mulmen wrote: post #37
scblock wrote: post #25

Earlier quoted context omitted.

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…

Does it have to be radar? Can it use ADS-B?

Little cropdusters and sport aircraft are who the anticollision lights are designed intended to protect, and many of them are not ADS-B equipped.

In the US, ADS-B is not required below 10,000 feet and when more than 30 miles away from the 30 largest commercial airports.

Re: Why do some radio towers blink?

#84

Post by marcosdumay »

genter wrote: post #82
xenadu02 wrote: post #36

Earlier quoted context omitted.

This is best practice for anyone who uses three phase power. A machine shop should connect 1/3 of their lights to each phase so it is immediately obvious if a phase gets dropped. Lots of equipment will suffer on two of three phases but with lower performance or even damage.

I was told that you want lights on all 3 phases so that you can see spinning things spin. If the lights are on single phase, they will dim 120 times a second, and the strobe effect can cause spinning things to appear stationary. With 3 phase, at least 1/3 of the lights are lit all the time.

That's a valid reason too. In an industrial environment full of rotating machines, thinking something is stationary because it's on the grid's natural frequency can be lethal.

It's way less of a problem with modern machinery, and leds will blink in uncorrelated phases in a frequency that is different from the grid's anyway.

Re: Why do some radio towers blink?

#85

Post by yjftsjthsd-h »

WalterBright wrote: post #67
dylan604 wrote: post #62

Earlier quoted context omitted.

Blinking attracts attention which is the real purpose. I'd assume based on how we detect motion more easily, these add a bit of "motion" to attract our attention

I know. But when I was programming LEDs for my single board computer, I found that blinking the LEDs used a lot less power. If the blink rate was fast enough, your eye did not distinguish that from the LED being on 100% of the time. I don't know if battery powered devices generally use that trick or not.

I mean, that's just PWM dimming, right? AIUI, pretty well ubiquitous for all LED dimming, including battery-powered.

Re: Why do some radio towers blink?

#86

Post by bluGill »

SoftTalker wrote: post #72
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?

I’ve driven through wind farms where the blinking tower lights are synchronized. Highly distracting.

If you look close - almost impossible in the dark - you will see that most wind turbines don't have any lights at all. Too many lights is a distracion but all the synchronized lights are an easy to understand 'stay away from this whole area'.

There are FAA rules on this.

Re: Why do some radio towers blink?

#88

Post by ranger207 »

Johnny555 wrote: post #29
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...

Speaking of, I was recently looking into what exactly makes lights NVG compatible, and found this informative PDF: https://www.consolite.co.uk/wp-content/uploads/2017/05/Basic...

tl;dr NVGs are sensitive to near IR so you want lights that are dim in those wavelengths (but not completely out since you still want to see them with NVGs) while still being bright in visible light. There's a neat picture of the flying controll tower on one of the UK's Queen Elizabeth-class aircraft carriers that shows two rooms with similar illumination levels in visible light, but under NVGs one room which isn't NVG compatible is massively brighter than the other. In the NVG-compatible room there were still a handful of panel indicator lights that were not compatible and lit up the whole space

Re: Why do some radio towers blink?

#90

Post by estimator7292 »

geerlingguy wrote: post #56
daemonologist wrote: post #15

Earlier quoted context omitted.

I believe it's usually GPS/GNS (they all receive the time via GPS independently, and flash at predetermined times). The FAA requires synchronization for many classes of obstruction because it makes it clear that you're looking at obstruction lights rather than e.g. brake lights or traffic lights on the ground.

Could they also use power grid sync? Not sure as I haven't talked to anyone in wind power, but grid sync would be pretty close to 1 Hz at least in the US. Building a product that would sync at 1 Hz via GPS that works in the US and other countries with 50 Hz power would be a little easier than syncing to grid phase though.

You can have each tower derive a perfectly stable 1Hz signal from the mains, but you have no way to synchronize those signals. Each tower's 'tick' starts at a random point in the 60Hz cycle.

You need an external, dedicated channel for this. You either synchronize with signals sent between towers or with a global signal from somewhere else (space). GPS broadcasts atomic time references for free, so everyone just uses that

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