Here ya go...
Harvey

Cool.
It's nice to see the actual results of one's efforts.
Hope it works as well on your tower.

 

Mornin' Guys. New member here so don't trash me too bad on my first day.

I'm a retired military electronics technician but it's been many years since I've been actively engaged in electronics. Nonetheless, I still understand the theory, at least up until the mid-1980s when all of the new and amazing technology started showing up! In a nutshell, my electronics education and experience ranges from vacuum tubes to CMOS digital ICs.

The reason why I'm here is because I need a cheap obstacle ("ob") light flasher for a 40ft tower about a quarter mile away from a small private runway. However, "flasher" would be a misnomer in this case since ob lights don't really flash anymore (at least not at night anyway) but, instead, exhibit a slow rise and fall as if fed by a very low frequency sine wave of about 1 cycle every four or five seconds. I'm looking for a circuit capable of driving a pair of common 60W incandescent bulbs in parallel. My electronics design skills, being as rusty as they are, have me thinking along the lines of a circuit based around a sine wave-controlled triac.

Of course, if inexpensive ob light flashers are already available for the amateur radio market, that would save me a lot of trouble (but also deny me a bit of fun).

Your opinions are solicited.

Many thanks!

Harvey

Hi Harvey
Old broadcast engineer here. I would almost BET the slow sinusoidal "flash" you're observing is actually a large incandescant lamp driven by an on off switch. The beacon lights on old radio towers have TONS of thermal mass, and they can take 15 seconds to drop out of the incandescent state. So, I believe you really do want a "hard" on off switch.

Traditionally, broadcast towers used a mercury switch with a rocker mechanism. Solid state switches normally use an SCR or TRIAC driven by a simple timer.

If your tower is "normal" there are probably two 620 watt beacon lamps in parallel....so there's some serious current being switched.

 

If your tower is "normal" there are probably two 620 watt beacon lamps in parallel....

Actually, my tower wasn't originally equipped with ob lights at all since it had a 1,200,000cp rotating beacon on top that operated every night from dusk to dawn. However, I'm turning it into an on-demand/part-time beacon so since it won't be lit up most of the night, I elected to put two 60-watters on it.

Thanks for your inputs though.

Harvey

 

Actually, my tower wasn't originally equipped with ob lights at all since it had a 1,200,000cp rotating beacon on top that operated every night from dusk to dawn. However, I'm turning it into an on-demand/part-time beacon so since it won't be lit up most of the night, I elected to put two 60-watters on it.

Thanks for your inputs though.

Harvey

Roger that. And yes, the FAA will definitely have something to say about the matter, so check the latest rules.
Eric

 

And yes, the FAA will definitely have something to say about the matter, so check the latest rules.

At 145 posts, I understand that this has become a long thread so it's not likely that everyone reads through the whole thing before posting their advice. Guys, the Tower-vs-The FAA-thing has been brought up by well-meaning posters many times now and has been shown to not be an issue each time.

To repeat...The FAA doesn't give a rat's pitootie about a 42ft tower nearly a forth of a mile off to the side of a private runway! While regulations do not apply in my situation, I've still sought official FAA advice throughout my project. In fact, I've voluntarily gone to great lengths to make sure my tower meets painting and lighting guidelines, even though they're not mandated in my situation.

A 42ft tower isn't going to catch and eat an airplane. If it could, every pine tree in the subdivision would have to be painted red and white and topped with a red light.

Please see the thumbnail in post 49.

Harvey

 

Hah, I can imagine the sight of a bunch of trees painted red and white with blinking lights on them!

It's good to see that it's working well... can't wait to see a vid of the tower with the modulator in place

 

... can't wait to see a vid of the tower with the modulator in place

And I'm anxious to post one but it'll be a week or so before I can. (Waiting on Mouser and McMaster orders to arrive.)

Thanks again to you, Crutschow, Alek, and the others for all of your help!!!

Harvey

 

Sorry about the delay in posting a video of the tower's ob lights in operation. I've been ordering the parts to finish the modulator's installation (i.e. an aluminum enclosure, terminal boards, switches, breakers, etc.)

In the meantime, Crutschow, would you mind giving me a brief description of your circuit's operation for my files for future troubleshooting?

Have a Happy Thanksgiving!

Harvey

 

Circuit operation:

U1, through U3 form a phase-shift sinewave oscillator. The feedback parallel RC on each opamp generates a phase-shift of 60° at the oscillation frequency to give 360° phase-shift around the loop (180° from the RC's and 180° from the op amp), as necessary for oscillation to occur.
D1 and D2 provide symmetrical soft-limiting to the signal for reduced signal distortion.

The signal goes through the clipper consisting of R8, R9, U7 and U8. U7 is a precision, programmable, shunt regulator which acts like a variable zener diode. Adjusting pot U8 controls the upper clip point on the sinewave.

The clipped signal is amplified by opamp U4.
Pot U5 adjusts the output amplitude.

Pot U6 adjusts the virtual ground level to the oscillator op amps which determines the zero level of the sinewave.
This is normally set so that the negative peak of the sinewave is just at 0V.

 

Thanks Crutschow.

Y'all have a Happy Thanksgiving!

Harvey

 

I FINALLY got a short video made of our Ob Light Modulator circuit in action.

It was taken at dusk so it's a dark video. It's best if you turn off any lights that shine on your computer monitor. Also, my 15 year old Olympus camera coughed its cookies a couple of days ago and I had to take the vid with my cheapie cell phone; which is why the background lighting varies in brightness as the auto exposure tries to do its thing.

My tower's ob (short for obstacle) light is an FAA-approved dual-lamp fixture with two 60w incandescent bulbs installed inside of aviation red globes. The ob lights are permanently installed and wired but the modulator circuit is temporarily wired into it pending completion of the tower's permanent control cabinet. (THAT'S a whole 'nuther subject!)

MANY THANKS to all who helped me with this project, notably Crutschow and Dr Jones. I couldn't have done this without y'all !!!

Y'all have a Happy Thanksgiving tomorrow!

Harvey (a.k.a. "Rabbit H")

 

Nice to see the completed circuit working to light the tower.
I don't often get to see the final results of any of my circuits.
Happy Thanksgiving!

 

Thanks for posting the video... awesome to see it in action!

Did you decide whether you were going to replace the incandescents with LEDs at some point?

 

I may go with LEDs sometime in the future but for now, I've got a case of rough-service 60w incandescent bulbs that were looking for work.

Harvey

 

I may go with LEDs sometime in the future but for now, I've got a case of rough-service 60w incandescent bulbs that were looking for work.

So they are not that difficult to change?

 

Actually, no they're not. I have to "harness up" and climb up a 40ft ladder but I already do that a couple of times each week anyway. (I'm still building the tower although it's nearly finished.) I may change my tune when I get into my 70s but I'm good for now.

Does AAC allow PMs?

Harvey

 

Yep! Click on the underlined member's name and a black window will pop up. On that window is a link to "Start a Conversation". From there. I am sure you can figure it out

 

There's no underline under his name and nothing on his profile page either.

Harvey

 

Ok, another way is to click on your name and look for "Conversations". A new frame will pop up, and there will be a button to start a new conversation.

 

That didn't work either. Perhaps I need to have a minimum number of posts (I've only got 87 since joining AAC) before I'm allowed PM privileges?

Harvey