High School Can orbiting lcds replace radio towers?

[Samson4]

Couldnt we put lcd type filters into orbit and modulate sun/moon light to produce high definition radio/tv? Obviously it would need to be large but it seems like it wpuld be much more efficient.

 

[Drakkith]

Couldnt we put lcd type filters into orbit and modulate sun/moon light to produce high definition radio/tv?

What is an LCD-type filter and what does it have to do with television or radio when placed in orbit?

 

[Samson4]

What is an LCD-type filter and what does it have to do with television or radio when placed in orbit?

Liquid crystal modulation, the type on lcd tvs. Modulating sunlight and using photodetectors to convert it into a digital signal.

Im assuming it takes less energy to twist the liquid crystal molecules than the electromagnetic energy it could modulate.

 

[berkeman]

Liquid crystal modulation, the type on lcd tvs. Modulating sunlight and using photodetectors to convert it into a digital signal.

Im assuming it takes less energy to twist the liquid crystal molecules than the electromagnetic energy it could modulate.

Okay, after re-reading your thread title and your posts a few times, I think I understand what you are asking. Whew!

So maybe you are asking if we could use transmission modulation of sunlight with a large LCD panel to repeat radio signals (like satellite radio) for receivers on Earth. Is that close?

problems I see..

• Would work only for the mid-day hours
• Would be very limited in bandwidth -- do you know about what bandwidth a typical communication satellite deals with?
• Would require receivers to be outside and be able to track very accurately the position of the optical repeater satellite

 

[Samson4]

I apologize. I thought it made sense. That "whew" made me laugh though.

Im talking about replacing a radio transmitter with these sunlight modulators. Shouldnt the amount of solar energy be high enough that detectors don't have to be outside?

 

[Drakkith]

Liquid crystal modulation, the type on lcd tvs.

Okay. I know what an LCD is, I just didn't know what an LCD-type filter is in this context. What are you filtering? Obviously sunlight, but what parts of the spectrum? The whole visible spectrum?

Modulating sunlight and using photodetectors to convert it into a digital signal.

Sure. This is trivial. But I don't yet see the connection to a TV/radio in orbit.

Im talking about replacing a radio transmitter with these sunlight modulators. Shouldnt the amount of solar energy be high enough that detectors don't have to be outside?

I have no idea what this means. What detectors and what are they no longer outside of?

You need to develop your idea or at least your explanation more. I don't even know the scale of what you're proposing, let alone any of the details of what this is even supposed to do.

 

[TurtleMeister]

I know what he's talking about. I think reflection would be better than filtering. But I don't see how it could be better than what we already have.

Two problems that come to mind right off are:
1. Would only work when there is no cloud cover.
2. Switching speed of LCDs would need to be improved by many orders of magnitude.

The up-link signal would still need to transmitted using conventional methods. No savings there. And our current satellites are not that inefficient. They use sunlight for power.

 

[Samson4]

I know what he's talking about. I think reflection would be better than filtering. But I don't see how it could be better than what we already have.

Two problems that come to mind right off are:
1. Would only work when there is no cloud cover.
2. Switching speed of LCDs would need to be improved by many orders of magnitude.

The up-link signal would still need to transmitted using conventional methods. No savings there. And our current satellites are not that inefficient. They use sunlight for power.

How would you use reflection?
1. No idea how to address this problem. I don't even know how far outside the filter's "shadow" you could detect the transmission.
2. It could be done with other types of electro optic modulators. I only proposed liquid crystal because they are cheap to make and light.

I said radio specifically because you don't need an uplink signal. I'm not sure about T.V though.

This is only a fun little thought experiment. I'm not planning on making this a reality. I would just like to know how feasible it is.

 

[Samson4]

Looks like someone already tried.
https://www.google.com/patents/US4573214

 

[berkeman]

I said radio specifically because you don't need an uplink signal. I'm not sure about T.V though.

Good point. Most radio programs are produced by aliens in orbit, versus TV shows who are produced by aliens on the Earth.

http://nerdreactor.com/wp-content/uploads/2015/09/MEN-IN-BLACK.jpg

 

[berkeman]

Looks like someone already tried.
https://www.google.com/patents/US4573214

My search for "bandwidth" in that patent does not yield any hits...

 

[Drakkith]

Looks like someone already tried.
https://www.google.com/patents/US4573214

Ah, now I understand what you're trying to do. Instead of sending out a microwave signal from a satellite that carries the information, you're re-directing sunlight and using a liquid crystal panel (or some other device) to switch the outgoing light on or off to modulate it with the information. Receiving stations would be "looking" at the satellite and receiving the modulated sunlight.

 

[Samson4]

Good point. Most radio programs are produced by aliens in orbit, versus TV shows who are produced by aliens on the Earth.

http://nerdreactor.com/wp-content/uploads/2015/09/MEN-IN-BLACK.jpg
View attachment 206026

Hahaha I read uplink and I thought upload, like with a wifi system in your house. Yeah the uplink would have to be conventional; but, it wouldn't have to be as powerful as conventional methods.

 

[berkeman]

Hahaha I read uplink and I thought upload, like with a wifi system in your house. Yeah the uplink would have to be conventional; but, it wouldn't have to be as powerful as conventional methods.

Glad you liked the humorous response.

Why would the uplink be any different? You still need to get the information up to the satellite at 24,000 miles to be downlinked...

 

[Drakkith]

Hahaha I read uplink and I thought upload, like with a wifi system in your house. Yeah the uplink would have to be conventional; but, it wouldn't have to be as powerful as conventional methods.

Why not?

 

[Samson4]

Ah, now I understand what you're trying to do. Instead of sending out a microwave signal from a satellite that carries the information, you're re-directing sunlight and using a liquid crystal panel (or some other device) to switch the outgoing light on or off to modulate it with the information. Receiving stations would be "looking" at the satellite and receiving the modulated sunlight.

Yes sir. I know it's not perfect.

 

[berkeman]

https://en.wikipedia.org/wiki/Communications_satellite

 

[Samson4]

The uplink could be amplified on the panel. It would be amplified again while modulating solar energy.

 

[Drakkith]

The uplink could be amplified on the panel. It would be amplified again while modulating solar energy.

It's already amplified on current satellites when it is received prior to processing/re-transmitting.

 

[Samson4]

https://en.wikipedia.org/wiki/Communications_satellite

You kept mentioning bandwidth. Is bandwidth a concern for something like radio? I thought you just needed power and resonant circuits.

 

[Drakkith]

Is bandwidth a concern for something like radio?

Err... what context? In terms of power or in terms of transmitting information?

 

[berkeman]

If you read the link I posted, communication satellites have huge BW. That's the only way to make them cost effective.

You might be able to do an amateur satellite project to do a limited number of audio channels (maybe 10?), but commercially you need many TB of BW to make the 100 million dollar launch fee justifiable.

 

[Samson4]

If you read the link I posted, communication satellites have huge BW. That's the only way to make them cost effective.

You might be able to do an amateur satellite project to do a limited number of audio channels (maybe 10?), but commercially you need many TB of BW to make the 100 million dollar launch fee justifiable.

Seems to me the reasons the gentlemen with the patent didn't bring it to market are covered in this thread. I only wonder if you could take it close enough to the sun that the signal could be picked up by 50% of the Earth at all times.

 

[davenn]

I only wonder if you could take it close enough to the sun that the signal could be picked up by 50% of the Earth at all times.

then you have to overcome even larger signal losses which are already huge

 

[sophiecentaur]

The uplink could be amplified on the panel. It would be amplified again while modulating solar energy.

You are clearly assuming Amplitude Modulation here. An amplitude modulator requires an input modulating power which is only a bit less than the carrier power. Where would this come from. except by sacrificing some of the sunlight that the satellite would be modulating. An LCD modulator would need to cover the whole area of the satellite collector / reflector
Instead of arm waving, it is necessary to do a proper Link Budget if you want to prove it's feasible. How much power will this satellite need to broadcast over its footprint?

We have a signal to noise problem here. In order to signal, using the (non-coherent) modulated light, passing through the satellite it would need to be visible in the presence of all the scatter of normal sunlight in the atmosphere. Both signal and the noise are in the visible spectral window - no advantage.
Conventional broadcast satellites make use of the wide band energy from the Sun and use it to produce a coherent modulated Carrier in a suitably chosen channel where there is relatively little interference due to scatter and which can be received by a sophisticated receiver which needs just a smidgen of a signal to give us good TV or Music programmes. There is really not contest, I'm afraid.

P.S. And what about CLOUDS? (That is the clincher, I think) Even in the Satellite broadcast bands, rain and clouds accounts for occasional drop outs with the available powers of broadcast satellites with tens of m² of solar cells.