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Using a Small Satellite Array as C-Band Receiver?
An anonymous reader asks: "Many local zoning ordinances prohibit big (6~8 ft) satellite dishes. Is it possible to use many smaller dishes to achieve the same effect as one big dish in picking up C-band transmissions? I know that moving large number of dishes, for satellite tracking purposes, would be a pain but are there any other issues?" Obviously building a satellite array is possible, but what are the engineering issues involved in building such a project? How much space is realistically needed? And, of course, the bottom line: how much would doing something like this cost?
Is it possible to use many smaller dishes to achieve the same effect as one big dish in picking up C-band transmissions?
Yes.
More detail?
Yes, do a google search on multiple antenna and radio astronomy. The math gets hairy sometimes, but it can be done. Might be more trouble than just getting a Dish Network thingy installed.
If tits were wings it'd be flying around.
Pardon me for asking, but what's left on C-band to watch?? I mean, there's other things in life beyond TV; what makes it worthwhile is that it's easy to get at - just push a button. So, I have to wonder (given that I don't know the poster's circumstances) why someone so technically literate is trying to learn how to spend hours and hours just to see "midget wrestling from Peru" or "stock reports in Korean"...
On second thought, it IS an interesting question in principle... so, it's ideal for Slashdot, the haven for techies who have too much free time. (which reminds me, I got WORK to do here!)
Perfectly Normal Industries
once you get the math worked out, the most expensive part won't be the used (stolen) dish network sattelite dishes, but the 20 or so erector sets you'll have to buy to turn them all at the same time for tracking. ...who uses C band besides that widely-pirated sattelite TV thing they had going in the late 70's/early 80's?
moox. for a new generation.
For those slashdotters like myself who found themselves asking a bajillion questions when C-Band was mentioned, check out the TVRO FAQ.
And just in case your wondering what TVRO stands for, here is a description of TVRO from the FAQ's introduction:
"TVRO is an acronym that stands for TeleVision Receive Only. Generally speaking, TVRO is the satellite distribution system for delivering programming to cable TV headends and systems."
Also, here are some interesting facts I gathered from googling around and reading the FAQ:
C-Band video is studio quality, it blows away cable and DSS/DISH satellite systems.
Commercial PPV stations like HBO are available but need decryption hardware.
Channels are leaving C-Band and switching to digital broadcasts, so the availability of C-Band channels is dropping.
Non-commercial much less homogenized content is available via satellite.
It's a bleeding edge technology, that you could build at home. Here are some examples and references:
JPL - NASA progress report on a fresnel zone lens.
Zone Plate (reflecting) Fresnel Antennas for Amateur SETI -- Part 1
You'll have to dig, but also use Google to find it.
You should be able to design a flat antenna from solid foam insulation with foil on both sides by removing the foil at the right places. There are design programs to do the math. Aiming is going to be tricky, but should be no more difficult than any other installation.
Good luck.
--Mike--
What you want to do is called Aperture Synthesis (or Inferometry) - It's what the VLA uses to combine the signals from it's 27 25m dishes to work like a single 130m dish.
There is some information on theory here, but I think building a device to actually do what you want will be very hard. Good Luck!
Well, it depends.
:)
If you are fine with purely mechanical steering (Note, the array must be turned in unison as one large unit), simple phasing lines will do.
If you want to have each dish stay in place and aim individually, you're screwed because electronic steering will be needed.
Hams have been doing this for years with monster Yagi arrays for moonbounce - But suffice it to say these were NOT to get around antenna restrictions.
http://www.uksmg.org/k6qxy.htm
retrorocket.o not found, launch anyway?
Many local zoning ordinances prohibit big (6~8 ft) satellite dishes.
If you are actually talking about government zoning and not covenants, conditions and restrictions (CC AKA deed restrictions), you're in luck. Get an FCC amateur radio license (anyone can get one for the $10 and a very basic understanding of electronics) and tell folks its a ham antenna. Don't mention TV reception.
The FCC's PRB-1 (here and here) is a limited preemption of zoning ordinances. Basically, local government must reasonably accommodate folks when it comes to antennas. A C-band dish in your back yard would certainly be reasonable.
(You may also want to bluff with Section 207 of the Telecommunications Act of 1996 which says that folks must allow dishes. It generally only applies to dishes less than a meter but some people won't read the entire document if you have a good poker face.)
Is it possible to use many smaller dishes to achieve the same effect as one big dish in picking up C-band transmissions?
Yes. Hams have beeing builing arrays for years to do moon bounce and whatnot. You can find some over the top pictures here. However, the infrastructure to create such a monster is substantial and is likely to run afoul of the same local ordinances you're trying to work around.
Overall, I don't see the point in using a big dish for TV anymore and an array of smaller dishes to act like a bigger dish seems pointless.
InitZero (k4mls)
They put up little white dome tent like structures to cover up the dish. The point was so people couldn't see where the dish was pointing/that there was a dish at all. all you need is something to hide it. Maybe a small privacy fence section with a nylon roof?
Other antenna solutions include a PVC "vent pipe extension" that fits over an existing vent pipe and include a built-in antenna.
Dishes are more problematic, but put up a fiberglass garden shed and then put you dish inside, create some fiberglass "art" and put your dish inder it. You can build your raydome out of wood, but be sure to use glue, not nails.
In theory, you could make a big dish out of a lot of smaller dishes but the combined area of the small dishes would need to equal the big dish. You would need to point the small dishes at the proper place and add all the small dish outputs in-phase.
... possible but not practical or cost effective.
Short version is
Check out this link. Look at the picture under 'Special Umbrella Dish Covers.' I remember seeing this idea -waaay- back when satellite was 'the only way to go' (still is, some would argue).
There's no wrong way, to eat a Rhesus...
I looked into doing exactly this about seven years ago and the prospects were dismal.
Building such a phased array is certainly possible, but the grief you'd have to go through to get it to work would be tremendous.
1. The total area of the smaller dishes would have to be at least the area of the big dish you're replacing, i.e. you'd need at least 45 18" dishes to equal the area of a single 10' dish.
2. You will need to steer your array of small dishes together to point at the desired satellite. The pointing accuracy of each would have to be on the order of a couple of degrees.
3. You'd need a phasing network to add the signals from each of those dishes together with the correct phasing. Note that the phasing will change as you steer the dish system. The network would have to have sufficient bandwidth to cover the spectrum of interest, which is not going to be easy. The design of such a monster would probably get you a PhD and a very good job at a major corporation.
4. The low noise amplifiers used (one per dish) would have to be very low noise indeed, since their contribution to the total noise of the phased signal goes as the square root of their number. If you've got 45 small dishes, each LNA would have to be only about 1/7 as noisy as would the amplifier for the single dish system.
I could go on, but realize what a horrible mess this would be. Arrays of dish antennas are used by radioastronomers for various reasons. The Very Large Array in New Mexico uses 27 25-meter telescopes to obtain very high angular resolution images. All of those antennas combine to become the equivalent of one 130-meter antenna.
A project of interest to those reading this is the Allen Telescope Array being built by the SETI Institute. It will use 350 6-meter TVRO dishes phased together to create one large radiotelescope. The engineering issues involved are extremely complicated.
Bottom line: it would be easier and cheaper to bribe your community's zoning board to give you a variance for a big dish, than it would be to build a phased array of smaller dishes. Even if you got prosecuted, the jail time would probably end up being less than the design time.
Hi there. I still use C-Band. All the channels I want to watch (Discovery, TLC, Fox News) for $100 a year. Add a MPEG-FTA receiver and get lots more unencrypted channels. Getting all the feedhorns properly in-phase on just one bird will be a major PITA. In order to aim at a different bird, the entire array would have to move together somehow in order to maintain the phase relationship of the combined antenna. Best bet is to put up the biggest offset focus dish your covenant will allow (probably 1 meter, you might get away with a 1.2m dish) and get the most sensitive C-Band LNB you can get, which I believe is a 15 degree. No guarantee though, bigger IS better. You want an offset focus dish so that the LNB is pointing at the sky instead of the ground. Less background noise in the sky...
An array of 17" dishes might do the job with the right feeds. You could phase match with coaxial cable. You'd need a different set of delays for each satellite you want to receive. You would need two or three arrays to cover the full sky. If you wanted a single fully steerable array that could choose anything on the sky, you're talking lots of electronics both for moving the dishes and forming the beams.
You could also do the job with a large number of dipole antennas, each with a bandpass filtered amplifier.... no need for multiple arrays, then, but more expensive on the electronics side.
Of course, any of these options is far more expensive than buying a new house in a place where you can put up a dish. :)
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Somewhere back in the '80s Radio-Electronics had an article about making a satellite antenna out of plywood. I'm relying on rusty memeory here, but as I recall it was made out of concentric square or rectangular rings. I think I rememeber the article saying it could have been made out of circular ones but the woodworking would have been a lot more hassle. Maybe you could make one and tell the authorities that it's garden sculpture or something.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Fresnel zone plates reflect part of the signal, and pass part; this gives them the potential to have a focus point on either side (front of back) of the zone plate. For the deck or patio it would be good to design it so that the focus point was above the zone plate and right about at your house; you mount a little feed horn pointing down at the deck roof, and nobody's the wiser.
If you aren't into quite as much DIY+math you might be able to make a flat-plate antenna and find a way to masquerade it as something else (an awning? maybe a solar water heater?) but IIRC most satellite transmissions are circularly polarized and that might present some difficulties; I've never seen a non-linearly polarized flat-plate antenna before.
Scientists restrict study to entire physical universe; creationist
For that matter, a hole might be your dish. A metal-lined hole. For aiming between several birds, a parabolic trench or a series of holes with a feedhorn on a rail... (yes, several feedhorns is probably cheaper and better).