How do satellite dishes for tv (Direct TV for example) communicate with satellites when there so small and pointed at a small area in the sky?
In: Technology
They don’t communicate with the satellite, they just receive a broadcast. The satellite broadcasts over a large area and every satellite dish in that area can receive the broadcast.
Revcieving a signal is all about signal to noise. You can generally amplify a signal as much as you want, but it also amplifies the noise.
The dish amplifies signals only from the direction it’s pointed, and there’s not a whole lot of other transmitters in space since putting satellites up there is expensive.
Add onto that satellites are generally allowed to broadcast at a much higher wattage, than say your cell phone or wifi. Wattage limits are based on the risk of interfering with other signals. So on earth you can’t just have a 100W WiFi router because it would ruin wifi for everyone else miles around. Satellites are more well planed and regulated, and of course there’s less of them.
Add on to that that most signal loss for ground transmitters is limited due to line of sight from the curvature of the earth. Antenna towers are tall to avoid having to transmit through the ground or through buildings, trees, etc.
And add onto that that even signal loss travelling through air is fairly limited. The atmosphere is mostly all concentrated in the lowest 10 miles. Traveling through space there’s no signal loss, from traveling through vacuum.
Well that dish thing is what helps.
It reflects the broadcast into the very small point on the receiver. Consider this the focal point. Kind of amplifies it
Thankfully as well. Your dish doesn’t need to send data back, only receive. It can be relatively small, where as the one in space is very powerful and broadcasts over a massive area
Noteworthy effects:
– you are just receiving. That makes it easier.
– There is not a whole lot of stuff between your dish and the satellite’s antennas that send the signal down to it. Just ~100km of air, the rest is empty space. Even though ~36000km sounds like a lot of distance.
– the dish gathers more of the signal and focuses it on the actual receiver. The bigger the better.
– the satellite is always in roughly the same spot so you can focus on it.
– I cannot find the exact numbers right now, but the TV satellite sends with at least 50 watts per channel, and has antennas that focus the energy on only a part of the planet (a continent usually)
Used to work for Dish Network.
So, the dish *generally* doesn’t talk back up to the satellite. It’s possible, but it requires a different dish and setup, and it’s only used for satellite internet, which isn’t what you were asking about.
It helps to think of the radio signals as a flashlight beam in a dark field. The little white lens part at the tip of the dish is called the low-noise block feed, or LNBF. *That* is the actual “antenna” and the rest of the dish is just a reflector to better focus the “light” of the signal.
It doesn’t need to be pointed *directly* at the satellite, but it’s got to be pretty damn accurate by human eyeball and hand tool standards. “Accurate” in terms of what your home garage tools can do and “accurate” in terms of spacecraft 22 thousand miles up are two *vastly* different things. The reflective dish makes that accuracy requirement a lot more flexible, and also affords a stronger signal to compensate for things like rain and clouds.
But all your receiver really needs to do is look at the equivalent of a flashlight in the sky, and determine the code from its blinking. Regular computer magic turns that really fast blinking into a data stream into video for your TV.
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