Antenna Arrays Could Replace Satellite TV Dishes 183
Zothecula writes "There was a time not so very long ago when people who wanted satellite TV or radio required dishes several feet across. Those have since been replaced by today's compact dishes, but now it looks like even those might be on the road to obsolescence. A recent PhD graduate from The Netherlands' University of Twente has designed a microchip that allows for a grid array of almost-flat antennae to receive satellite signals."
Why? (Score:2)
Surely the small parabolic dish is more compact/efficient than an antenna array? I looked at the article but it doesn't show any pictures of what these new antennas would look like.
It would be cool if something like this could be used to replace the big, bulky antennas needed for Broadcast TV and Radio.
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Ok, but I live in an apartment in an old (historic, something like 117 years old so far) building and they won't let us attach anything to the exterior walls/roof. My windows all face north. I want to use a satellite to receive more programming. I am adverse to paying Comcast one more dime.
What are my options again?
This sounds great, if it would work for me. The 16 foot ceilings mean I could talk the wife into letting me mount even a mesh in the ceiling area of the apartment, if I could conceal it afterward
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The rules may be illegal.
FCC Rules on Antenna/Dish placement [fcc.gov]
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"The rule allows local governments, community associations and landlords to enforce restrictions that do not impair the installation, maintenance or use of the types of antennas described above, as well as restrictions needed for safety or historic preservation. Under some circumstances where a central or common antenna is available, a community association or landlord may restrict the installation of individual antennas. The rule does not apply to common areas that are owned by a landlord, a community association, or jointly by condominium or cooperative owners where the antenna user does not have an exclusive use area. Such common areas may include the roof or exterior wall of a multiple dwelling unit. Therefore, restrictions on antennas installed in or on such common areas are enforceable."
Looks like the restriction is probably legal. He doesn't have exclusive use of the south-facing wall (or any use, apparently), and a 117-year-old house is certainly on the Historic Register.
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Depends on where you live. Where I live, buildings that new are most certainly NOT on the historic register unless they happen to have other historical significance besides age. Keep in mind also that owners can choose to *not* put their buildings on the historic register -- the designation has drawbacks as well as adv
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Keep in mind also that owners can choose to *not* put their buildings on the historic register -- the designation has drawbacks as well as advantages.
What is the historic register? (I'm not American.) Over here the government decides. There are various restrictions on what you can do to these buildings, depending how historically interesting they are. An owner can contest the decision, but that's it -- and ignoring the restrictions is a criminal offence.
In college, I lived for a year in a house that had been built in the 1840s. It was a piece of shit, and the owner was a slumlord. The walls were literally falling down
The owner here would be required to maintain a historic building. The whole point is that it doesn't fall down...
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Ya know, I really wasn't going to worry over it. I was getting my mind all made up to just move over to a completely wired-delivery life, and go ad-hoc like the up and coming trend seems to be (or: like the trend seems to be if you listen to twit.tv) and have been trying to get my wife to understand just what Hulu and the like are, and to use DSL for that delivery, but then I read that there may be a way to do it from inside the apartment.
Ah well...
As for putting things on the roof, nope. But installing a p
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Hook up a dish, they cannot stop you, you might have to put it on a pole in the yard. The FCC is a higher authority than your landlord.
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The common thing to do here is to mount the dish to one of the vents up on the roof(which are almost NEVER in view of the street). That way, it's a 5 minute job to remove it if it needs to be. Just loosen the mount and slide it off. Zero damage. Of course, you're out of luck unless you're on the top floor. Yet one of many reasons I never rent on the lower floors.
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your options are to contact the FCC and state to see the laws you have in your area concerning the right to receive TV.
Your Local Historic district gestapo cant do crap to keep you from putting up a satellite TV dish.
http://www.fcc.gov/mb/facts/otard.html [fcc.gov]
verify your rights and then have one installed and tell the historic commission to stuff it in their rectum.
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Or deal with it? I don't have a balcony.
The rule does not apply to common areas that are owned by a landlord, a community association, or jointly by condominium or cooperative owners where the antenna user does not have an exclusive use area. Such common areas may include the roof or exterior wall of a multiple dwelling unit. Therefore, restrictions on antennas installed in or on such common areas are enforceable.
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> Ok, but I live in an apartment in an old (historic, something like 117 years old so far)
Historic?! You must be American! My building was built in 1810 and has 18" thick solid walls (try getting WiFi to go through that - or a drill bit long enough to run the Cat 5 though).
But yes, we have the same problem - no dishes or even aerials are allowed on our building, so hopefully this technology will allow those of us in listed/protected buildings to get satellite-based services.
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I don't normally feed the trolls, but in this case:
Meh, I'm glad that I'm able to walk to 40% of the places I want to visit instead of needing to use my auto. I chose to live in an area that was downtown and if the price I have to pay is the lack of satellite TV, well, I guess that's the price I'll pay to try and live a little bit greener. Not that I need a satellite anyways. I'm a bit more interested in getting out and seeing my community than staying at home watching TV.
I have a feeling, however that you
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It sounds a lot like a phased array to me. Not really new.
And why? Well some people might not like the look. They will fair better in high winds and with snow loads. Also they will work much better for vehicles. Combine it with a GPS and it can track a satellite while you move.
It could also switch between satellites on it's own.
In theory you could even use it with none geosyc satellites. As one comes into view you could switch beween them in a very rapid mannor. That could allow for a much lower latency i
Re:Why? (Score:5, Informative)
The big advantage I see to this is two-fold: 1. Mounts flat so it is much less of an eyesore. Also you could conceivably hide it behind something that is radio transparent. 2. Can be pointed via software, so that the physical installation only needs to be pointed in the rough direction of the satellite.
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#2 is even bigger than huge, because it removes the need for geosync satellites, meaning someone could orbit some satellites at a much lower orbit and the phased array could track them in real time. That means much cheaper costs put your birds into low-earth orbit, much lower power the satellite has to put out and much higher frequencies available for signal density, and much lower latency. Screw TV, we're talking viable satellite telephone and low-latency satellite Internet access. Hell, you could launc
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Take a look at a modern battle Tank or Destroyer class missile cruiser - they have flat angled sides with these roundish "targets" in the middle. A close-up reveals those circles to be composed of hundreds of individual antennas in a circle-shaped array. Our AEGIS missile cruisers were the first to get this, now land vehicles like tanks and the new ADS (Active Denial System - the "death ray" weapon) use phased array antennas like the ones on shipboard, just smaller...
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Because you can't easily use a parabolic dish which needs to be aimed accurately on a car, caravan/RV/mobile home etc. This technology could potentially make it easier to resolve the weak satellite signals which would normally require a dish, resolvable by a static antenna array which could be omnidirectional. As the article implies, it might mean that digital radio actually *works* :)
non-problem solved! (Score:2)
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Those may not be valuable for you, but they are valuable for someone out there. The article was about the science, not the marketing. Come back in 12 months for the marketing take on it. I'm sure they'll have thought up more than I did in the last 30 seconds.
Phased array are physically robust (Score:2)
Relevant info? (Score:2)
So, I'm no expert on signal analysis, but I understand the whole concept of Satellite Dish arrays and why we have those big fields of Giant Dishes pointed at the stars to read incoming data.
This article doesn't seem to point out any of the information that might be handy. How far apart do your antenna's need to be, how big exactly do they need to be, how many, all that good stuff.
For all I know, it might need a hundred of centimeter long antenna's spread across the entire length of my yard. Would THAT make
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For all I know, it might need a hundred of centimeter long antenna's spread across the entire length of my yard. Would THAT make a dish obsolete?
Well, think of that antenna array as being punji sticks: http://en.wikipedia.org/wiki/Punji_stick [wikipedia.org]
No need to scream "Get off my lawn!" anymore.
Just let the buzzards pick up the carcasses . . .
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Because it isn't all you know, the answer is "yes" it will make dishes obsolete. Assuming the worst and speculating on that doesn't help things. Wait till you see the antenna array the size of a sheet of A10 paper mounted to the roof of your house.
When people talk about making something else obsolete, they are usually know what they* are talking about.
*Exceptions include Marketing Droids and brain dead CEOs
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The problem is, we often hear that from the marketing droids and CEOs. Sometimes they get a tech to be their puppet for that statement.
The other issue is that sometimes knowledgeable and very rational people make that claim without understanding the unadulterated irrationality of the modern market.
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Antenna elements in an array are usually about 1/2 wavelength apart. L-band, 1ghz to 2ghz, has a wavelength of 20 to 30cm. So... half that, assuming 1/2 wave separation.
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It's the Netherlands. European satellite TV is synonymous with ku-band, 10.7-12.7 GHz.
The tech being described would be frequency-agnostic; the big question is how many elements it can manage. With higher frequencies and shorter wavelengths, the ability to phase-shift becomes coarser and coarser (the time-delay adjustment needed is measured in picosecond increments at 10GHz), and doing so digitally is not the easiest task. If the phasing adjustments are done digitally, the "dedicated hardware" approach that the professor seems to be using would be the solution to the expense that would be in
Sigh... (Score:2)
Marcel van de Burgwal's system would not need to be aimed. Instead, the antenna array would electronically "aim" itself. It is a concept similar to the LOFAR project, in which numerous antennas located across the northeast Dutch countryside are linked together to form a virtual radiotelescopy dish. LOFAR requires a lot of calculations and fast communications, as would van de Burgwal's system - that's where the chip comes in.
I
Where's the problem? (Score:3, Insightful)
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I don't think DSS dishes are even 5lb.
I think this might allow more placement options, but there are likely major trade-offs. If you want your phased array antenna to allow you to place the antenna flat on the side or top of a house (or RV), then you reduce reception sensitivity to the intended satellite vs. a parabolic dish of the same area pointing at the satellite. Parabolic dishes themselves don't consume power, whereas this chip does. Having a lot of small antennas also means wiring and complexity,
Re:Where's the problem? (Score:5, Insightful)
The problem is that the dish weighs 25 pounds, offers significant wind resistance, cannot be used while the vehicle is in motion, needs to be aimed at a satellite each time the RV is moved, and depends on geosynchronous satellites or continuous aiming with a servomotor. It's also ugly, but that's an aesthetic problem, not a practical one.
The advantage of phased array systems like this would be that you don't need to deploy and aim the dish once you reach your destination. You simply turn the system on, and the handful of flat metal pads glued directly to the roof of your RV (plus possibly a couple or three on each side if you're in high latitudes) can pick up the signal without moving anything around. The pads can be utterly unobtrusive, installed permanently, and offer no wind resistance at all.
There are no moving parts because the array is "aimed" only in a virtual sense by software. You'll still need a good bit of surface area to pick up a useful signal, but that surface area can be flat and spread over a larger area in smaller bits (you don't need one big contiguous dish, just a few squares or rectangles of surface area). It can even track a moving satellite and keep it in view (or track a moving or geosync sat while you are driving down the road).
No wind resistance when driving, no moving parts to wear out or replace. Just a few metal bits glued flat to the roof, wired to a computer that compensates for the time difference between the various signals. You could get signal from multiple satellites in different parts of the sky simultaneously, or based on which one happens to be in the clearest view at the moment, without carrying around a sky chart and signal meter or depending on a complex array of servos to do it for you.
Phased arrays are not new. It just takes a lot of number-crunching and a lot of power, which up until now has been accomplished more cheaply by hammering out a parabolic dish and aiming at a stationary target, saving all that number-crunching.
This guy's algorithm and chip design may (or may not) make it cheap enough to be practical for routine use.
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Or you could just not watch TV while you're driving....
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I would like to have satellite TV on my phone. Now then - where exactly do I attach the phone to my dish?
Secondly, while it probably won't work while indoors (can't see any satellites), it'd probably work while I'm in the garden, on the beach or on my bicycle.
There you go - we just found a problem for this thing to solve, and it only took me about 2 seconds to come up with it. I'm sure th
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There are many cool applications of the chip. Receiving satellite TV on a smart phone isn't one of them. The array would still be bigger than the phone. It could be less awkwardly shaped and a LITTLE smaller than the regular 18 inch dish, primarily because it would be perfectly "aimed" while the dish needs enough margin for error.
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Well I know for sure that the local news vans running around the city will love this technology. As it is, they have to stop and spend several minutes linking up everything. Now imagine them just parking and being online in 30 seconds. Or while still moving, even.
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This does appear to be a solution in search of a problem. Today's dishes are already tiny enough to easily mount on an RV.
One potential use for these would be with the upcoming O3B network [wikipedia.org] of MEO satellites [wikipedia.org]. Currently, the ground station design is very expensive, because the dishes need to target the next satellite coming over the horizon about once every 20 minutes. A flat panel such as this would remove the need for mechanical elements in the antenna array. Definite win.
O3B is a very interesting service to the developing world, where the odds of pulling a fibre-optic cable any time in the next decade are often close to nil.
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Mobile is certainly a market. But there's a lot of money spent installing and fixing DBS dishes around the world. The amount of money saved troubleshooting would be tremendous.
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My parents won't switch to satellite, even though they hate their cable provider. Why? They think the dish looks ugly and don't want one on their house.
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see beamwidth: http://www.kyes.com/antenna/navy/basics/antennas.htm [kyes.com]
Been done for years... (Score:2)
Phased Array antennas (Score:5, Informative)
Phased-array [wikipedia.org] antennas really do work but they are not new. The nice thing about them is that they have electronic steering, so they can steer really fast while a conventional antenna of equivalent size would take much more time to move.
The problem with articles like this (and their Slashdot introductions) is that they always come off as student makes big scientific break-through rather than student applies well-known science.
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It sounds like the break though here is in a much cheaper controller, such antenas have been around 50 years (the first nuclear aircraft carrier, Enterprise, had one), and are available for RV & SUV use (big blob on roof, $$$).
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Indeed they are SO SO not new that anyone around when they were used in the late 80's and early 90's would not have been alive when they were invented in 1905. :-)
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Good sound-bite (sound-byte?), but Grandmother managed to make it just fine into the early 90's and was born just a bit before 1905.
People are living longer and longer, and we're only talking about 85-90 years (heck, my grandmother used to tell us about being a girl and watching this new-fangled thing flying overhead, the airplane).
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And since your typical home satellite antenna has no need of moving... this sounds like a solution in search of a problem. Doubly so since current antenna a pretty small. Shrinking them further requires either increasing their transmission frequency, or improving the amplifiers - not shifting to phased arrays.
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True, they don't need to move. Except when an ice storm loads enough ice up to move it. Or wind moves it. Or the idiot installer couldn't be bothered to point it correctly the first time. Or the neighborhood kids decide to repeatedly throw basketballs at it. Or any of a dozen other ways that crap happens and you need to re-point the dish.
Being able to more securely mount it in "roughly" the right direction, and electronically "point" the array would be a big advantage.
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If only somebody would invent a mobile radio phone (Score:2)
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So, how can I use phased array antennas to improve my OTA DTV reception?
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You don't need them for this. Build a Gray-Hoverman antenna.
Actually, you should also look for other problems. Before I bought a UHF meter, I thought I wasn't getting enough signal. But the meter said otherwise. The problem was front-end overload or intermodulation swamping the weaker stations. Get rid of your present store-bought preamp, and any other amplifiers in the line, they're too noisy. Get a preamp from Research Comms [researchcomms.com], they are really pricey but worth it. Remember to order the power supply and outd
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Lots of ways. Re-point (electronically) for every channel, even multiple simultaneously. Phase-cancel an interfering signal based on its direction. A more complicated system with dynamically-changing phase delays could probably reduce the impact of dynamic multipath.
Recent graduate with PhD != student (Score:3, Informative)
RSN (Score:2)
The real news is the last paragraph of the article:
"Van de Burgwal also discovered that his multi-processor chip would work well for digital radio reception on smartphones, due to its low energy use. The technology is being further developed by U Twente spin-off company Recore Systems."
There is more money to be had from a general purpose antenna receiver in smartphones. At the very minimum, faster ROI which is what will drive the faster development/implementation into the consumer market.
What the article d
and how well does this work with rain fade? (Score:2)
and how well does this work with rain fade?
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Basically as well as existing antennas. Rain fade happens, pretty much by definition, in all the stuff between the transmitter and the receiver. You can't engineer something in the receiver to make it not happen because it has already happened before the signal gets there.
You can make the antenna bigger to get more signal. That's true with existing technology, that's basically still true with whizzy modern phased array systems. Ideally, the phased array stuff w
Another story that never dies (Score:2)
Substantially the same story has been popping up regularly for about twenty years. It's like the flying car story. It's always just around the corner, but it never reaches the market, at least not at a competitive price.
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Never reached the market? What about the squarial from BSB in the UK in the 90s (http://en.wikipedia.org/wiki/Squarial)
D.
It gets even better if you make an array of dishes (Score:2)
The observatory consists of 27 independent antennas, each of which has a dish diameter of 25 meters (82 feet) and weighs 209 metric tons (230 Short tons).
http://en.wikipedia.org/wiki/Very_Large_Array.
The flat surface to dish per the original article is a trick where you vary the electrical distances of each of the patches on the flat surface to shift the signals as though they were spatially received by a dish shaped surface. You can apply the same trick to dish antennas which have much better directional g
Array info (Score:5, Interesting)
A collection of links on antenna arrays at a ham radio antenna design site: http://www.dxzone.com/catalog/Antennas/Array/ [dxzone.com]
It's not all about signal strength. Sensitivity these days is rarely an issue; the electronics in the receiver are excellent. Of greater relevance are polarization, rejection of off-axis noise, directivity, and the ability to reject signals from adjacent bands. There are also issues of setup difficulty, and this is what the primary focus of the design in question is.
Aiming a dish antenna is a chore, and high winds which shake a parabolic dish can cause signal strength to fluctuate dramatically. An electronically controlled phased array can, by introducing delays to various antenna elements, "steer" itself and lock onto a satellite with great accuracy (within a few degrees of the direction the array is aimed). A small antenna, perfectly aimed, will outperform a larger antenna poorly aimed, and if the antenna's controller can aim itself without physical adjustments many thousands of times per second, wind and a... coarse job of aiming the antenna are non-factors.
A military example: PAVE-PAWS [wikipedia.org], a 435Mhz missile detection array used by the US Air Force. The antennas in question are made of thousands of smaller elements (a single dipole element at 435MHz is about 35cm long), do not move, but the transmitted radar beam and the reception-aiming can be extremely precise. The more elements you have, the narrower the beam but the higher the gain.
L-band, commonly used by companies like satellite TV providers, is 1 to 2 GHz. An array of 16 log-periodic (wideband) antenna elements would therefore be 60cm square. A 4-element array would be 30cm square. Pretty compact, and if it gets rid of the most common cause of poor signal strength (a poorly-aimed dish), it's a win.
What's new is cheaper, lower power (Score:2)
What's new isn't a phased array antenna for satellite TV, you can get them now, though they might cost several thousand dollars vs less than $100 for the small dish.
The Gizmag article mentions the new chip being cheaper and lower power as opposed to what is currently used. Besides being "flat" and sticking out a phased array satellite TV antenna would be easier to install as it could be aimed electronically rather than physically pointing the antenna. It would still need to be pointed in the general direc
Got an 802.11n receiver?Then you have this at home (Score:3, Interesting)
802.11n directionality is achieved by phase summing the signals from 2 or more dipoles.
Yawn.
Oh yeah the patent for 2 or more phase locked receivers on one chips is pretty old. So even getting it onto one chip is not new.
http://www.freepatentsonline.com/7636554.html
A MIMO radio transceiver to support processing of multiple signals for simultaneous transmission via corresponding ones of a plurality of antennas and to support receive processing of multiple signals detected by corresponding ones of the plurality of antennas. The radio transceiver provides, on a single semiconductor integrated circuit, a receiver circuit or path for each of a plurality of antennas and a transmit circuit or path for each of the plurality of antennas. Each receiver circuit downconverts the RF signal detected by its associated antenna to a baseband signal. Similarly, each transmit path upconverts a baseband signal to be transmitted by an assigned antenna.
Flat is the old black. (Score:2)
Granted, they are not phased array so you need to aim them, but flat Ku band satellite antennas have been around for over a decade around here. Here is a random example a quick googling turned up: http://www.techradar.com/reviews/audio-visual/digital-tv-receivers/sqish-selfsat-h10d-420191/review [techradar.com]
/greger
Not at all new (Score:2)
This isn't new, BSB here in the UK had a flat satellite receiver which they called the "Squarial". It was a phased array, like other people have said.
Now, if it could be electronically adjusted to pick up different satellites without having to physically move it, that would be interesting. I believe some military radars do this.
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OK, that'll teach me to not RTFA properly. Apparently it *can* be electronically adjusted.
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So can the TracVision units which have been on the market for a few years.
Not new at all (Score:2)
Phased arrays for DirecTV reception have been on the market for at least a few years. Here's one:
http://www.solidsignal.com/pview.asp?mc=06&p=KVHA7&d=KVH-TracVision-A7-InMotion-SUVMiniVan-DIRECTV-Satellite-TV-Antenna-System-(A7)&c=Satellite%20Dishes%20for%20SUVs&sku= [solidsignal.com]
Supposedly the student has developed a signal processor that will reduce power consumption and/or cost, but the article is REALLY slim on details as to how they did this and whether they really have made any significant breakthr
ship radar without moving antenna (Score:2)
cheap weather radar
- just to name a few applications beside simple satellite reception.
- It is not a ground breaking technology - but also computers were known before the PC came!
Yes, it does work. (Score:2)
This is not new or even especially clever compared to some antenna designs. And it does actually work and has benefits.
Aegis cruisers use a phased-array radar set that solves a multitude of problems - flat panel does not need to be physically articulated or rotated, it 'aims' virtually instananeously, allowing the system to track multiple targets with high precision, and I bet it consumes substantially less power than a moving dish or other types of antennae.
Replacing various reflectors with an array, one
It will still work (Score:4, Funny)
if you connect it with Monster cables.
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Raw size does matter here. A larger receptor is better.
Which explains why the small dishes now do similar things that the old big ones did?
I suspect it *is* the software that can filter out/account for that interference on a slightly less quality signal that makes the smaller dishes do just fine.
Bigger is better at the extreme end of a broadcast range; i.e. listening for something from outside the solar system or something incredibly weak compared to background noise.
I would also bet that the satellites being used now are more powerful than the origina
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does it snow a lot where you live ? If it does, can you please tell me the model of your small dish ?
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Forget about snow. A friend used to lose his TV signal about 45 minutes before it rained.
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How long ago was that? Up until I got U-Verse I had been a Dish customer and I never lost signal even during hurricane Ike (I live in Houston). Well at least I didn't until the power went out. My next door neighbor lost her comcast cable about an hour after the storm hit and it was out for six weeks.
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After 2000, before 2004 for that particular person. I've seen the same on other dishes more recently, but I don't see it very often (satellite that is).
May be our latitude (I'm a fair bit North of you) and because our dishes are only tilted up about 15-20 degrees ... who knows. But, I've definitely seen it on numerous occasions, and still occasionally see it in bars when they have satellite TV.
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But during heavy showers you'll need more amplification than under a clear sky.
How you achieve the amplification, larger dish or better electronics, is fairly immaterial for the end result.
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Raw size does matter here.
A larger receptor is better.
Which explains why the small dishes now do similar things that the old big ones did?
Or it could have something to do with the wavelength of the radio signal being received. Longer wavelengths require larger receivers. For an example compare your eyes (wavelengths measured in angstroms) with a radio telescope (wavelength measured in meters). (of course, power and efficiency also enter into it, but the bigger factor at play is the wavelength)
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I suppose the old sats might use a different wavelength than say DirecTV sats I guess.
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Have the wavelengths of the sat broadcasts changed?This about using a new type of antenna to handle an existing broadcast, not trying to receive a different signal, no? I suppose the old sats might use a different wavelength than say DirecTV sats I guess.
Yes, the old C-band has a much greater wavelength than the present Ku-band.
Re:No (Score:4, Informative)
GP is correct - the dish size has all to do with the gain of the antenna, not the resonant frequency. The actual antenna is at the focal point of the dish and it's length IS frequency-critical. The surface area of the dish directly corresponds to its gain.
The reason we no longer use giant 6' dishes is twofold - because they are using 24 GHz instead of 5 GHz means the antenna at the focal point is much smaller, and the area of the dish is relatively the same size - with relationship to the wavelength - which is also much smaller.
The other reason is the peak power of, say the DirecTV sats, is as high as 150W for some transponders, whereas the older C-Band stuff was about 10W peak.
Dishes typically are designed to produce somewhere around 30dB of gain, which is 1000x magnification of the signal over a straight dipole with no reflector.
Re:No (Score:5, Informative)
GP and YOU are mildly incorrect. WaveLength of the signal is impotant to the gain of the dish. a 5ghz signal has less gain on a 5 foot dish than a 20ghz signal does.
a 3 meter dish at 5 ghz has 21.704db of gain.
the same dish at 20 ghz has 54.415db of gain....
massively more gain on the same size of dish simply because of the frequency of the signal.
you also ignore that the LNA's used today are 20 times better than the ones from only 5 year ago.
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"The actual antenna is at the focal point of the dish and it's length IS frequency-critical."
The dish is a simple parabola, it's focal point is not frequency dependent. Its gain IS frequency dependent however. Achieving the same gain at half the frequency requires double the dish size (or, double the frequency and you can halve the dish size for the same gain).
As long as the dish is smooth enough its focal point is not frequency dependent. At the extreme low end things fall apart (i.e. the dish becomes o
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Yes, and no.
The old satellites did use a longer wavelength, it is true. In both cases, however, the parabolic reflector in use is several orders of magnitude larger than any dimensions dictated by the wavelength. The only tuned element (which is where wavelength comes into play) is found at the narrow end of the feedhorn, up in the LNB.
The new ones are smaller because digital signalling has replaced analogue, in turn making error correction possible and sufficient for 99% of the time, and by the fact that
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I don't believe that DSP implementation in receivers was responsible for smaller antennas. If you have some references you can point me at I would appreciate it.
In a 40 Mbs tv digital stream there is about 17 Mbs of forward error correction. This allows the base fairweather signal to still be usable when rain/snow deteriorates the reception. This means that instead of losing your reception when it rains, you can still watch Jersey Shore (or Big Bang).
DSP implemented communication sets usually don't hav
Re: (Score:3, Interesting)
Your attribution of this effect is wrong.
The old 2m-3m satellite dishes were for receiving analogue signals. By going digital, it is far easier to detect and sufficiently correct for using a very weak signal. That gets the dish size down to about 1m. The other 50cm difference in size is due to the newer satellites using a higher power output.
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It's the difference between C band and Ku band. C band is 5.850–6.425Ghz while the Ku Band is 12 to 18 GHz. you need a LOT LARGER dish for C band to get the same gain that a small dish at Ku band will get. THIS is the reason why today's home TV dishes are smaller. NOT technology or power. In fact a Lot of TV is still available on the C band. I have friends that have a couple of the big dishes and get a lot of channels, two pay for HBO and STARZ and get about 40 channels of them in the pack for
Re: (Score:2)
Satellite dishes are smaller now because the original C band transponders were power limited compared to the current Ku band transponders. As well, antenna size is related to wavelength so equivalent antenna designs for a high frequency (Ku band) will be proportionately smaller than for a low frequency (C band).
So... sat-TV receiving dishes are smaller because both the satellite transmit power and frequency increased.
Digital Signal Processors (DSPs) can do a lot, but all receiver processing (analog or dig
Re: (Score:2)
The change in size was due to a move to Digital, NOT just an improvement in reception technology.
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Antenna performance (in this case a parabolic dish) depends on several factors. The old C-Band dishes needed to be 10 feet across due to relatively low power on the downlink, and because the gain of a dish depends on its size relative to the wavelength of the signal. C-Band used a 4.7 Ghz signal, which has a wavelength of about 6.3 cm, or about an 2.5 inches. Later dishes received Ku band signals, where were about 11 Ghz, which have a wavelength of 2.7cm, or a little bit more than an inch. Proportionately
Yes - RTFA! (Score:3, Informative)
Raw size does matter here. A larger receptor is better.
If you RTFA (yes I know it is Slashdot but hope springs eternal) you'll see that the system uses a GRID of flat antenna which it combines to simulate a larger antenna. By altering how the signals are combined i.e. the delays between them you can "point" the antenna at different sources. Hence you not only have a large detector from combining several smaller one but you can also point the thing without having to mechanically move it. It's brilliant idea and one that radio astronomers have been using for qu
Size matters but... (Score:2)
Re: (Score:2)
Being susceptible to interference does not mean that a minimum size is required or has been reached for the detector.
You could just as easily and with as much validity use the same argument on the old style large satellite dishes. However for most consumers' needs the new smaller ones work just as well, are easier to deploy and cheaper.
These new arrays when they come to market will probably be just as good for the average consumer, smaller and thus easier to deploy.
I'm already getting sat radio through a d
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Raw size does matter here.
That's what she said.
Power spectral density (Score:3, Interesting)
The amount of spectrum bandwidth required to transmit a few hundred audio channels is a fraction of what is needed to transmit a few hundred TV channels.
So given a constant amount of power available, the power spectral density when transmitting audio only is significantly higher than when transmitting television.
Also, Sirius uses satellites in Tundra or Molniya orbits (I don't remember which), which are geosynchronous, but not geostationary.
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Sirius Satellites Radiosat 1 through Radiosat 3 fly in geosynchronous highly elliptical orbit (Tundra orbit) in a 24-hour orbital period. The elliptical path of its satellite constellation ensures that each satellite spends about 16 hours a day over the continental United States, with at least one satellite over the country at all times. The orbit allows the satellites to broadcast from directly overhead the continental United States, avoiding the problem of large buildings or objects blocking the signal an
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2) Sure it takes more power to transmit over a larger frequency, but if you have a device transmitting across 10Mhz @ 1 watt, it will take more power than a device transmitting across 20Mhz@1mW. Just because you are transmitting a large amount of data (or small) doesn't mean you can't have high power.
3) When the Sirius satellites are actually transmitting, they are actually FURTHER out than a geostationary orbit. It's actually kind of neat. They are