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?

answer

[PD]

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.

Re:answer

[jeremy_fsu]

I showed this to my dad who owns a satellite equipment company [tampamicrowave.com]. He's actually done this with Ku-band, his comments:

You can phase combine smaller antennas to do the job of bigger ones. It isn't that easy and can be done only over a part of the band due to the lengths of the coaxes between the dishes and the phase combining parts. The basics are that you find a suitable frequency power combiner for the number of dishes you want to combine. You must make all cables to the combiner the exact same length within 1/2 inch. Then you need a phase shifter (available from Pasternack) in each line. You must aim them individually with the use of a spectrum analyzer. You have to place some microwave absorber material over each lens or lay it in the dishes you are not aiming. Aim one dish at a time and then start with one dish as the first one. then uncover the absorber material from each one one at a time while monitoring the spectrum analyzer. After each one is uncovered, adjust it's phase shifter to combine in phase with the signal displayed. This will set the dishes in phase with each other (hence the name phased array). You will see about a 3 db increase in the signal strength each time you get the phase correct on the successive dishes. Keep in mind that you narrow up the bandwidth also as you combine more dishes and that is why pointing is critical. Obviously this is a fixed satellite configuration. I've done this for up to 4 ku band 1 M dishes deployed to Saudi Arabia and it does work.

Why?

[bscott]

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!)

Re:Why?

[NoMoreNicksLeft]

Generally, anywhere on the planet, C band offers at least 1500 channels.

Besides, he never said he was going to watch it afterward...

total cost

[Hadlock]

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?

FAQ

[EMIce]

For those slashdotters like myself who found themselves asking a bajillion questions when C-Band was mentioned, check out the TVRO FAQ [cs.uu.nl].

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.

Re:FAQ

[h2odragon]

C-Band is analog and uncompressed. no artifacts. If you get the dish alignment a bit off, or have a warped dish / old LNB / bad or long cable run, quality degrades. There are a bunch of satellites up there, but much of their capacity is unused. Few normal channels are unscrambled (broadcast networks are scrambled. IIRC, so is PBS.).

These are drawbacks, but then again, you get fun things like 12hr simpsons marathons (syndication feeds for TV stations), and raw footage of news events as they happen (site to studio feeds, where they point a camera at the news and leave it. no talking heads telling you what they think they're seeing). Considering the cost of big dishes nowadays, its well worth it.

Helical arrays [seaveyantenna.com] can be used in place of a large dish; but there's some issues that make them less than optimal, i gather. It'd probably be cheaper and easier to disguise your Big Ugly Dish somehow.

Stealth, the Fresnel Zone Plate reflector

[ka9dgx]

The ordinance prohibits a dish, but they wouldn't notice a properly disguised Fresnel Zone Plate antenna. The only visible component would be the feedhorn.

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. [nasa.gov]
Zone Plate (reflecting) Fresnel Antennas for Amateur SETI -- Part 1 [setileague.org]
You'll have to dig, but also use Google [google.com] 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--

A way to hide a Fresnel zone plate

[Spamalamadingdong]

If you own your home, you can put the foil on the back of a sheet of white fiberglass sheet instead of over foam insulation. You can then install this in place of a part of your roof, or as a roof over a south-facing deck or patio. It'll look like a poor man's skylight.

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.

Aperture Synthesis

[steve.m]

What you want to do is called Aperture Synthesis (or Inferometry) - It's what the VLA [nrao.edu] 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 [merlin.ac.uk], but I think building a device to actually do what you want will be very hard. Good Luck!

Not that hard...

[Andy Dodd]

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

These guys do it

[shoppa]

See their setup at this web page [nrao.edu]. Some stats:

The Very Large Array, one of the world's premier astronomical radio observatories, consists of 27 radio antennas in a Y-shaped configuration on the Plains of San Agustin fifty miles west of Socorro, New Mexico. Each antenna is 25 meters (81 feet) in diameter. The data from the antennas is combined electronically to give the resolution of an antenna 36km (22 miles) across, with the sensitivity of a dish 130 meters (422 feet) in diameter.

Re:These guys do it

[hubie]

However, to phase the signals from all the telescopes the radio astronomers have to time-tag the signals coming in and combine the data via post-processing. They use atomic clocks at each telescope to do the time-tagging. Combining the signals electronically only works in practice when you have telescopes (usually two) watching a source pass overhead (so that you are not trying to actively phase the telescopes).

Goverment on Your Back? Quote PRB-1

[InitZero]

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 [arrl.org] and here [fcc.gov]) 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 [aol.com]. 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)

Do what the NSA did for years.

[starfighter_org]

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?

Re:Do what the NSA did for years.

[JUSTONEMORELATTE]

Or simply put in a toolshed with a fiberglass roof instead of a steel one. Would local zoning prohibit a 9' - 12' square toolshed too?

Re:Do what the NSA did for years.

[careo]

You can buy a microwave-transparent fiberglass rock to cover your dish. They come in all shapes and sizes from a tiny Dish Networks size to a BUD (Big Ugly Dish) size for C-Band.

Get two big ones, half a dozen small ones, tons of sand, and call it a Zen rock garden. Who could be so callous as to deny your religious freedom?

The Satellite TV FAQ [faqs.org] has a whole section on how to get a dish if your neighbors won't let you.

Re:Do what the NSA did for years.

[SEWilco]

Somebody...probably the NSA... also painted a smiley face [pari.edu] on a dish used to track satellites. So spy satellites could see that we were watching them.

It was a small dish, so only a spy satellite had good enough cameras to see the face. (You now can buy a satellite photo of the place and the dish itself is barely visible)

Hide in plain sight

[MountainLogic]

HAMs have been dealing with these type of issues for decades. One very simple solution is to hide it in plain sight. Want to put up 10 meter antenna without ticking-off your neighbors? Put up a 10 meter wooden flag pole and glue your antenna to the pole. Heck, your cranky neighbor may very well help you raise your "flag pole."

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.

Re:Hide in plain sight

[Teun]

I've seen pictures of a concrete dish disguised as a fountain.
It was build by a Dutchman running a Dairy farm in Saudi Arabia.
This obviously works best nearer to the equator.

Urban Camo

[Mu*puppy]

Check out this [clearsat.com] 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).

In theory, yes. In practice, no.

[dlleigh]

Is it possible to use many smaller dishes to achieve the same effect as one big dish in picking up C-band transmissions?

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 [nrao.edu] 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 [seti.org] 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.

Some c-band thoughts

[Adrenochrome]

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...

Yes, an array is possible.

[SETIGuy]

C-band is about 6 cm wavelength, 5 GHz on the high end. That means you'll need to know your antenna positions to a centimeter or better, so you can phase the signals to 33 picosecond before adding them together. The better you phase match your signals the higher your effective gain will be.

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. :)

Make it out of plywood

[unitron]

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.

Think Under The Box

[SEWilco]

Does the regulation prohibit a hole in the ground? Instead of having the dish above ground, disguise it with landscaping...build a brush-covered bowl around it. Paint the dish in green camouflage -- or light shades of gray if your part of the country gets snow. Or dig a hole and put the dish down there.

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).