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Why do some radio towers blink?

jeffgeerling.com

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Re: Why do some radio towers blink?

#111

Post by [deleted] »

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.

[deleted]

Re: Why do some radio towers blink?

#112

Post by cesarb »

jamesbelchamber wrote: post #8
pizzalife wrote: post #5

This blog post has a really verbose format. TLDR; White lights are used during the daytime, red lights at night (less annoying), towers under 200 feet don't need blinking lights.

It's a transcript of the video at the top.

> It's a transcript of the video at the top.

Which is not obvious at all if you have JavaScript disabled by default, since it only shows up as a blank space, which could also be a blocked ad or an image which failed to load correctly.

The first few times I saw one of these transcripts with video at the top (IIRC, it was on Practical Engineering, not this site), I thought it sounded odd but didn't get that it was a transcript. Only later did I find out that there were videos (and they're great).

Re: Why do some radio towers blink?

#113

Post by user_7832 »

CableNinja wrote: post #95
dylan604 wrote: post #70

Earlier quoted context omitted.

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…

You only need about 40hz to make it seem on all the time, TVs (before 2020, maybe earlier) only did 25hz-ish. You can actually play pretty ridiculous tricks on the brain if you know this. For example, in VR, in a large enough room, you can slightly alter the angle the player sees inbetween frames. This alteration makes the brain think youre slightly offset from where it thinks you should actually be. This allows you…

Fwiw, these "tricks" are nice for some, but cause headaches for those who're PWM sensitive (like me). I can easily see the flicker of eg my Pixel 5 screen (which iirc is around 300ish hz?), and it hurts my eyes.

Fortunately, some folks like Philips make bulbs that are very low or zero flicker.

Re: Why do some radio towers blink?

#114

Post by hylaride »

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.

Back in the analog TV days, I could see the flicker on the 50hz PAL/SECAM signals whenever I visited Europe, especially when the screen was white and in my peripheral vision. I always wondered why it didn't drive everybody nuts, but then I got used to it. I did always wonder if there was a way they could have eliminated that (maybe they did in more expensive TVs that fired off at double the reference signal and not in cheap TVs in hotels/bars?).

Re: Why do some radio towers blink?

#115

Post by OJFord »

ssl-3 wrote: post #98
genter wrote: post #82

Earlier quoted context omitted.

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.

How did that work, do you suppose? How does one connect a lamp to 3-phase power? Are/were there 3-phase fluorescent tubes available? Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously? Without such malarcky as shadows or inverse-square to muddy our vision? Or maybe a multiplicity of single fixtures with 3 tubes -- on…

> Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously?

That's exactly what they mean, yes. Some lights on L1, some L2, some L3.

> And even then: Doesn't it still strobe somewhat at (5032)=300 or (6032)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?

No, because the phases are overlapping, there is no point in time where they're all off. There'd be local dimming of course, depending on their position etc., but light for all of the second.

Re: Why do some radio towers blink?

#116

Post by clort »

dylan604 wrote: post #60
barbazoo wrote: post #14

These beacons are also great for navigation. Aeronautical charts usually show the color/pattern of the light. You can use those as points to triangulate your position.

IIRC, light houses are marked on charts similarly. The lights have different patterns, maybe color too?? Maybe not on aeronautical charts though.

Lighthouses are usually white. They used to rotate (sweeping the beam) but tend to flash now I think. Nautical charts show the elevation of the light, the visibility ranges and the pattern of on/off (eg Fl (2) 10s 41m 17NM). Some lights are sector lights, so red/white/green depending on your position, they indicate if you are in the correct approach channel.

It can be really confusing approaching a port at night. Never mind the city lights behind, and the cars driving about. 20+ lights flashing at different rates in the dark, some of them disappearing for seconds at a time. Oh, and if you turn your light on to refer to the chart, there goes your night vision!

Boat masts above 25m also have blinking red lights for the low flying aircraft (I guess its a bragging point)

Re: Why do some radio towers blink?

#117

Post by geerlingguy »

mjevans wrote: post #99
geerlingguy wrote: post #68

Earlier quoted context omitted.

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

You'd probably have better timekeeping from a reasonably connected Pi with a common NTP daemon (take your pick, some are easier to configure / query), and a realtime-ish thread to emit your PPS signal on a GPIO or similar. Probably more robust than line of sight, and able to pool with other NTP servers in your home-lab (and beyond).

True, but I'm not thinking of a practical method, just fun. I already have GPS derived time here, but that's been reliable and boring!

Re: Why do some radio towers blink?

#118

Post by noir_lord »

hylaride wrote: post #114
genter wrote: post #82

Earlier quoted context omitted.

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.

Back in the analog TV days, I could see the flicker on the 50hz PAL/SECAM signals whenever I visited Europe, especially when the screen was white and in my peripheral vision. I always wondered why it didn't drive everybody nuts, but then I got used to it. I did always wonder if there was a way they could have eliminated that (maybe they did in more expensive TVs that fired off at double the reference signal and not i…

simple answer is grid frequency in europe is 50hz, in the US and Canada it's 60hz.

Early TV's synchronised to the grid frequency (and drew the entire screen on each cycle) - also remember TV's where analogue to start with (and operated at large voltages/transformers) so if they didn't sync with the grid electrical noise becomes a big problem with the power supply.

In monitor terms it reduced jitter.

Re: Why do some radio towers blink?

#119

Post by noir_lord »

ssl-3 wrote: post #98
genter wrote: post #82

Earlier quoted context omitted.

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.

How did that work, do you suppose? How does one connect a lamp to 3-phase power? Are/were there 3-phase fluorescent tubes available? Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously? Without such malarcky as shadows or inverse-square to muddy our vision? Or maybe a multiplicity of single fixtures with 3 tubes -- on…

> How does one connect a lamp to 3-phase power?

You typically connect 1/3 of lamps on one phase, one third on another and so on.

In the UK we use a 230V single phase system for most things (industrial/commercial often use 400V) (if all three phases are in use it's 400V - you may see it as 415V but we harmonised with Europe to 400V) so lighting expects that 230V anyway, you still have a common ground, you just run the live for each phase to the lamp/light.

Power delivery to homes is in effect a single phase out of a three phase supply with each house (often but not always) wired in sequence, so house 1 is Phase 1, house 2 is Phase 2, house 3 is Phase 3, house 4 is phase 1 and repeat.

We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey

When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).

Re: Why do some radio towers blink?

#120

Post by MisterTea »

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.

At work we run a lot of machinery with motors and its obvious when phase loss happens. From my office I can tell if the lights go out/dim and the usual shop "hum" becomes a buzzing grunt that is immediately identifiable. Older machines have to be manually powered down but the machines I rebuilt have phase loss protection in the PLC thanks to a power monitoring terminal in the IO (Beckhoff EL3453.) Since the PLC is on 24V DC I have a capacitor backup module fronted by a 24V PSU that takes the 480V three phase power which tolerates a phase loss. The machine safely stops the process and shuts down the pumps and any other AC loads, then waits to be manually powered off as the PSU and DC side doesn't care.
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