Re: satellite dish design

[Jeep4by4]

OK, I've been reading the satellite dish design thread and wanted to ask some questions without cluttering up that thread so I'll ask here.<p>If I'm reading what's being said correctly, it seems that the size of the dish has nothing to do with the wavelength trying to be captured correct? That the parabola only reflects the signal (any signal) and the "feed horn" is what determines what the dish recieves? <p>So if that's true, I have a newtonian reflector telescope (basically a mirror that focuses the light on an eyepiece) could I use that as a giant microphone if I put a mic in place of the eyepiece? <p>Just curious to see if I'm understanding correctly.<p>[ August 17, 2005: Message edited by: Jeep4by4 ]</p>

[Chris Smith]

If you have a reflector type telescope, the answer is yes. <p>If you have a “Glass lens type” the answer is no, for sound. <p>The glass lens blocks the sound, it doesn’t reflect sound. <p>For example on sat dishes..., the size of the dish is the ability to focus more or less waves of energy onto a single spot. [the antenna]<p> There are basic limits and sizes best suited for different frequencies, however size is about gain.<p>You can purchase 8 foot dishes, 10 foot dishes, 12 foot dishes, all the way up to 16 foot dishes, and all of them are for C band reception. Small ones produce weak signals, large ones produce strong signals in the feed horn antenna. They are collectors of weak signals. <p>If you use one of these large dishes for a "Direct TV" signal [higher frequency], you will always have a 100% signal because in most cases a 3 foot or smaller dish is all that is needed for Direct TV due to their signal strength in the sky, and their digital signal. Direct TV has a 50 to 250 watt signal, C band barely has a 10 watt signal and at 25,000 mile away, that’s dim. [pico watts on earth]<p>You can receive a weak C band channel on a small dish, but the signal is poor due to the weak transmissions in the sky, and low gain from the dish size. Same thing for the space telescope, its 10 feet or more in diameter to collect weak signals.<p>Also, for different frequencies of light, sound, and Microwaves, it’s the parabola that matters. The actual curve formulae.<p> Light, sound, and MW all bounce off the surface but they bounce at a slightly different “angles of incidence”.<p> This is why they make different parabolas for different applications. <p>However, with a sufficient dish surface area, and even a incorrect parabola angle, you can use them for sound and light even if they are cut at a perfect angle for MW due to the bulk in gain from a large surface area. <p>Is this perfect in that all the energy is aimed exactly at the center point, no.<p>But the error is minimal and the gain is so High you wont notice the minimal loss from all the gain. 100 gain minus a 5% loss still = 95% gain.<p>The only time this will be obvious is if you try to convert a microwave dish into a optical telescope. It will work, however it will be less than stellar. <p>However if you chose to make it into a Helios-stat or solar collector, it works just fine and the loss is completely unnoticeable.<p>[ August 17, 2005: Message edited by: Chris Smith ]</p>

[Jeep4by4]

Great thanks!

[jwax]

Jeep- let us know if you hear anything interesting, anything at all, from the heavens, OK?

[Chris Smith]

A ten inch Newtonian glass dish can look into the heavens real far, and hear a shit load here on earth. <p>A quick swap of the eye piece and Walla, sound!<p>Imagine the space telescope? <p>Way too expensive for the job at hand, but its tireless and doesn’t ask why.

[Jeep4by4]

I'll probably never try it, unless I get a wild hair, I was just curious.<p>Maybe I'll listen in on the neighbors though...

[Chris Smith]

Large Newtonians are very expensive, but I have even done that on a old oxidized 6 inch lens before getting it re-silvered.
It works.