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Why do some radio towers blink?

jeffgeerling.com

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Re: Why do some radio towers blink?

#61

Post by anyfoo »

lxgr wrote: post #55
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.

Wouldn't the mains frequency be a common clock source, if nothing else? But presumably these lights at least have battery backup, given the obvious risks in case all of them were to fail at the same time due to a grid issue.

Yeah, the mains frequency qualifies, if you explicitly use that.

(Doesn't solve the problem if you want them to be in sync phase-wise, i.e. blink at the same time or similar, but at least they won't drift apart, which was what this is about.)

Re: Why do some radio towers blink?

#64

Post by dylan604 »

geerlingguy wrote: post #57
pizzalife wrote: post #31

Earlier quoted context omitted.

Yes, reading transcripts is a terrible way of ingesting information in my opinion.

But at least you can scan and read through it instead of having to sit through an entire video :)

and thank you for doing it, at least!

next, you'll be expected to turn that into an outline, index cards, and then a full term paper lest you be ridiculed for your work on the internet!

Re: Why do some radio towers blink?

#65

Post by scblock »

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.

Definitely GPS. Other methods have been used in the past--I remember reading operating reports from a wind farm nearly 20 years ago that slowly brought all its lights in line with each other over several months--but these days you can buy mainstream lighting with the GNSS receiver built in from a number of suppliers. They make it easy.

For wind farm use most also have an external input for ADLS triggers, though that usually also requires a separate controller and communications connection to manage the ADLS signals.

The flashing red lights are L-864 type. The requirements are 20 to 40 flashes per minute (FPM), and typically 30 FPM is used.

Re: Why do some radio towers blink?

#66

Post by scblock »

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?

The FAA document says "sensor-based" but every installation I have seen in the US uses radar.

Re: Why do some radio towers blink?

#67

Post by WalterBright »

dylan604 wrote: post #62
WalterBright wrote: post #54

Blinking uses less power.

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.

Re: Why do some radio towers blink?

#68

Post by geerlingguy »

scblock wrote: post #65
geerlingguy wrote: post #56

Earlier quoted context omitted.

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.

Definitely GPS. Other methods have been used in the past--I remember reading operating reports from a wind farm nearly 20 years ago that slowly brought all its lights in line with each other over several months--but these days you can buy mainstream lighting with the GNSS receiver built in from a number of suppliers. They make it easy. For wind farm use most also have an external input for ADLS triggers, though that…

Hmm... maybe I could build a 1pps GPSDO based on light flashes from nearby towers, then. No need for my own GPS antenna!

Re: Why do some radio towers blink?

#69

Post by georgefrowny »

anyfoo wrote: post #58
georgefrowny wrote: post #42

Earlier quoted context omitted.

A cheapo 20ppm quartz watch crystal definitely doesn't drift by a second every few minutes, but it will over about about half a day at maximum error. A 5ppm one (still sub one Euro) will keep a second about every two days. A 0.5ppm TCXO can be had for about 15 Euros from Mouser and that gets you two weeks. If you have shared line power you can just use that and everything will be locked in sync forever. If you don't…

Well, yeah. I was sort of assuming that you won't use a TCXO or even just a cheapo quartz crystal, because it doesn't make a lot of sense: You've now thrown money at something that will relatively quickly desync anyway. I mean, sure, the TCXO will mean that you only start seeing a phase difference between the two after weeks instead of minutes, but what's the point of that? I you want them to be at the same phase, yo…

Well yes, obviously, but I'm just being a internet pedantic about "a few minutes".

Re: Why do some radio towers blink?

#70

Post by dylan604 »

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.

all dimmable LEDs use blinking, but interesting case for your suggestion for an even more efficient use of a "steady" LED. what blink frequency did you use to keep it from being visible to the eye? did it not dim the overall brightness to a meter? early LEDs were atrocious with their slow blink rates that quickly scanning across them could see it, but even more noticeable if you pointed your camera at them. now, they blink incredibly fast, fast enough even for some slo-mo to not strobe.
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