# Why do some people still have those big ass satelite dishes in their backyard? **URL:** \ **Category:** Factual Questions\ **Created:** [November 25, 2008, 10:02pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486 "2008-11-25T22:02:48Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![hajario](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hajario/32/171_2.png) [@hajario](https://boards.straightdope.com/u/hajario)\ **Post date:** [November 26, 2008, 4:18pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/21 "2008-11-26T16:18:51Z")
> [@Spartydog](#): > > Then he would take the scrap to the recycler and pocket about $200. I tired that with mine but no recyclers in my area were interested. Of course that was 15 years ago and the prices of metals now may make it worthwhile. ---
**Author:** ![Aestivalis](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@Aestivalis](https://boards.straightdope.com/u/Aestivalis)\ **Post date:** [November 26, 2008, 4:23pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/22 "2008-11-26T16:23:16Z")
> [@Max\_Torque](#): > > Depending on where you see them, it may be a part of their security system. > > Some of the larger convenience store chains, like Allsups and 7-11, no longer have the little VCR in back whirring away, recording images from the security cameras. Instead, the data from the cameras is actually sent up to a satellite, where it is downloaded and stored at a central location. No more “stealing the tape” by a robber to conceal his identity. It’s also likely to be their network connectivity. Prior to cable or DSL internet being available, lots of gas stations hooked into a satellite network to get access back to their corporate network. Lots of our stations are still connected that way, so the managers have access to internal web-mail. ---
**Author:** ![Troy\_McClure\_SF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troy_mcclure_sf/32/4150_2.png) [@Troy\_McClure\_SF](https://boards.straightdope.com/u/Troy_McClure_SF)\ **Post date:** [November 26, 2008, 4:27pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/23 "2008-11-26T16:27:59Z")
> [@Lambo](#): > > It’s been [done,](http://www.cockeyed.com/incredible/solardish/dish01.shtml) but should really be done a lot more. [Indeed](http://www.gizmodo.com.au/2008/06/mit_students_build_solar_dish_that_can_melt_you_your_family-2.html). Mythbusters also invited these kids out to do it again in the Bay Area. ---
**Author:** ![1010011010](https://avatars.discourse-cdn.com/v4/letter/1/ea666f/32.png) [@1010011010](https://boards.straightdope.com/u/1010011010)\ **Post date:** [November 26, 2008, 4:39pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/24 "2008-11-26T16:39:47Z")
> [@Hampshire](#): > > What’s with those small to mid size satellite dishes on top of gas stations? > I thought maybe it was to receive info on current pricing but wouldn’t just be easier with a basic internet connection? Look at gas stations in your area and see if there are any overhead cables. There usually aren’t. Whether this is by statute or because they have to dig everything up to put the on-site petrol storage tanks anyway and underground cabling looks nicer, I don’t know. It’s probably fiendishly difficult to dig up a cable run at a gas station. Satellite internet could just make more sense than dial-up or upgrading infrastructure for DSL/Cable. It would also still work when phone/cable might not. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [November 26, 2008, 5:06pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/25 "2008-11-26T17:06:44Z")
Always make sure you don’t get lasagna anywhere near the dish. bonus points to whomever gets the reference ---
**Author:** ![diggleblop](https://avatars.discourse-cdn.com/v4/letter/d/ac91a4/32.png) [@diggleblop](https://boards.straightdope.com/u/diggleblop)\ **Post date:** [November 26, 2008, 5:16pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/26 "2008-11-26T17:16:03Z")
we have one from when we used to use that system. We now have cable and just never decided to dig up that big old heavy dish and do anything with it, so there it sits in the back yard. ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [November 26, 2008, 6:27pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/27 "2008-11-26T18:27:50Z")
I’ve heard that one could get a LOT of radio programming wit them, but don’t rememeber if a descrambler was needed. Brian ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 26, 2008, 7:17pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/28 "2008-11-26T19:17:35Z")
> [@](#): > > I think they could be quite useful as solar concentrators, as mentioned upthread. Cover them with tinfoil, stick a diverging lens just in front of the focal point to parallelize the rays, mount a gimbaled mirror at the focal point to direct the beam to your other equipment, and you have a 1980’s-style solar-powered “Death Ray” source of hot bright light for all sorts of uses. Sadly, this won’t work. Your parallelized beam won’t be any brighter than a normal beam of sunlight. An object at the focal point doesn’t see a source that’s any hotter than the actual sun; it just sees the sun filling a much greater portion of the “sky” (i.e., the entire area of the dish). An object at a distance looking into the parallelized beam would only see sun filling the area of the lens. Hopefully **CalMeacham** wanders by this thread to elaborate more: He’s corrected me on this misconception twice. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [November 26, 2008, 7:22pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/29 "2008-11-26T19:22:50Z")
> [@Chronos](#): > > Sadly, this won’t work. Your parallelized beam won’t be any brighter than a normal beam of sunlight. An object at the focal point doesn’t see a source that’s any hotter than the actual sun; it just sees the sun filling a much greater portion of the “sky” (i.e., the entire area of the dish). An object at a distance looking into the parallelized beam would only see sun filling the area of the lens. > > Hopefully **CalMeacham** wanders by this thread to elaborate more: He’s corrected me on this misconception twice. Okay, now I’m really curious. How does taking the solar flux from n square metres of dish and reflecting it all through a much smaller area not increase the flux intensity in the area? Same total power, much less area. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [November 26, 2008, 7:36pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/30 "2008-11-26T19:36:48Z")
> [@Chronos](#): > > Sadly, this won’t work. Your parallelized beam won’t be any brighter than a normal beam of sunlight. An object at the focal point doesn’t see a source that’s any hotter than the actual sun; it just sees the sun filling a much greater portion of the “sky” (i.e., the entire area of the dish). An object at a distance looking into the parallelized beam would only see sun filling the area of the lens. > > Hopefully **CalMeacham** wanders by this thread to elaborate more: He’s corrected me on this misconception twice. I hate to object to Chronos on physics, but I’m not getting something. Sure, an object will not get sunlight that is not (within a given tiny fraction of angular area) brighter than normal sunlight; it will just see the same-brightness sun over a much larger portion of the sky. Same area intensity + larger area = cooked whatever at the focal point. But why isn’t it possible to stick a lens near the focal point that will focus down the rays to a smaller area (thereby increasing the intensity)? ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 26, 2008, 7:56pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/31 "2008-11-26T19:56:53Z")
> [@Chronos](#): > > Sadly, this won’t work. Your parallelized beam won’t be any brighter than a normal beam of sunlight. An object at the focal point doesn’t see a source that’s any hotter than the actual sun; it just sees the sun filling a much greater portion of the “sky” (i.e., the entire area of the dish). An object at a distance looking into the parallelized beam would only see sun filling the area of the lens. > > Hopefully **CalMeacham** wanders by this thread to elaborate more: He’s corrected me on this misconception twice. You’ve forgotten more about physics than I’ll ever know, so I’m assuming there’s some confusion about the question being asked. Surely you can use a foil lined dish as simple solar concentrator? It sounds like you’re possibly answering a question related to using the dish as a solar telescope in some fashion. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 26, 2008, 9:04pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/32 "2008-11-26T21:04:54Z")
> [@](#): > > Surely you can use a foil lined dish as simple solar concentrator? That you can do. The problematic part is putting a lens at the focal point to turn it into a long-range death ray. The key is that the energy output or intensity you get from an object depends on its effective temperature, and its apparent area. So for normal, un-concentrated sunlight, you’re getting the effects of a 6000 Kelvin source, covering a very small apparent area of the sky (a circle half a degree across): That’s enough to provide a comfortable level of heat, but doesn’t set things on fire. Now, there’s nothing you can do to increase the effective temperature of an object or its image: That would violate the Second Law of Thermodynamics. All you can change with a solar collector or the like is the apparent size of your hot source. So while we see a 6000 Kelvin source covering a half-degree diameter circle, the piece of cardboard at the focal point of that mirrored disk sees a 6000 Kelvin source covering a 60-degree diameter circle, which heats it up a lot. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [November 26, 2008, 9:40pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/33 "2008-11-26T21:40:37Z")
> [@Chronos](#): > > So while we see a 6000 Kelvin source covering a half-degree diameter circle, the piece of cardboard at the focal point of that mirrored disk sees a 6000 Kelvin source covering a 60-degree diameter circle, which heats it up a lot. Sure, that’s true for whatever’s at the focal point of all those converging rays coming off the dish. But if I insert a diverging lens, doesn’t that effectively map the angular area subtended by the dish to a circular beam cross-section? The sunlight might not be of a higher colour temperature, but it would be a lot more intense. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 26, 2008, 9:52pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/34 "2008-11-26T21:52:54Z")
> [@Chronos](#): > > That you can do. The problematic part is putting a lens at the focal point to turn it into a long-range death ray. > > The key is that the energy output or intensity you get from an object depends on its effective temperature, and its apparent area. So for normal, un-concentrated sunlight, you’re getting the effects of a 6000 Kelvin source, covering a very small apparent area of the sky (a circle half a degree across): That’s enough to provide a comfortable level of heat, but doesn’t set things on fire. Now, there’s nothing you can do to increase the effective temperature of an object or its image: That would violate the Second Law of Thermodynamics. All you can change with a solar collector or the like is the apparent size of your hot source. So while we see a 6000 Kelvin source covering a half-degree diameter circle, the piece of cardboard at the focal point of that mirrored disk sees a 6000 Kelvin source covering a 60-degree diameter circle, which heats it up a lot. I’m a bit lost. Are you saying that a lens cannot focus or re-direct already concentrated sunlight to another point away from the focal point of the concentrator? Can’t a prism redirect light. Why can’t a prism (for example) redirect focused high energy light away from the focal point of the collector to another location? ---
**Author:** ![1010011010](https://avatars.discourse-cdn.com/v4/letter/1/ea666f/32.png) [@1010011010](https://boards.straightdope.com/u/1010011010)\ **Post date:** [November 26, 2008, 10:01pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/35 "2008-11-26T22:01:07Z")
I think **Chronos** ’s just saying that the Death Ray Spec requires temperatures hotter than 6000K, so solar power is never going to cut it. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 26, 2008, 10:05pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/36 "2008-11-26T22:05:10Z")
> [@1010011010](#): > > I think **Chronos** ’s just saying that the Death Ray Spec requires temperatures hotter than 6000K, so solar power is never going to cut it. So the[speculation](http://www.tmth.edu.gr/en/aet/1/13.html)that ancient Greeks used giant polished metal dishes or mirrors on cliffs overlooking the sea to set enemy boats on fire at a distance is quite impossible? > [@](#): > > ARCHIMEDES: CRANES, CATAPULTS, MIRRORS > > Archimedes played a major part in defending his natal city of Syracuse against a protracted Roman siege, as the designer of a host of weapons and machines to repulse the attackers. These fall into three main categories: a) cranes (or ‘claws’) that lifted enemy ships out of the water and dashed them against the rocks, b) catapults of every size and description that hurled bolts and stones varying distances, and c) the mirrors that focused sunlight on the ships and set them alight. This latter invention has become legendary, and much has been written about whether such a thing could in fact have been possible in the time of Archimedes. Most experts, and particularly foreign experts, were persuaded that the construction of such a system was a myth, despite the weight of literary evidence supporting the story, until engineer Ioannis Sakkas succeeded in demonstrating that it was indeed possible. Sakkas used 70 copper-plated glass lenses, with diameters ranging from 1.70 to 0.70 metres, and his experiment was carried out at the Palaska Training Centre on the island of Salamina on November 6, 1973. Sakkas placed his 70 lenses in a circle, and succeeded in focusing the sun’s rays on a small boat, built in the same way as Roman craft and equipped with the same sort of materials, lying 55 metres away. In less than three minutes the boat was ablaze. Sakkas’ experiment was reported around the world, and caused quite a stir. Three previous tests had also produced satisfactory results, and together they confirmed that Archimedes did indeed set fire to Roman ships. While we do not know the full effect of this conflagration, the psychological impact on the enemy must have been terrible. That, of course, is why his feat acquired the status of a legend and is still talked about to this day. ---
**Author:** ![1010011010](https://avatars.discourse-cdn.com/v4/letter/1/ea666f/32.png) [@1010011010](https://boards.straightdope.com/u/1010011010)\ **Post date:** [November 26, 2008, 10:18pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/37 "2008-11-26T22:18:15Z")
> [@astro](#): > > So the speculation that ancient Greeks used giant polished metal dishes on cliffs overlooking the sea to set enemy boats on fire at a distance is quite impossible? Did the enemy boats catch fire at a temperature less than ~6000K? It’s a heat transfer question. You have a hot rock. How do you heat something until it’s hotter than your heat source? You don’t. You can’t. No matter how many hot rocks you use. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [November 26, 2008, 10:20pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/38 "2008-11-26T22:20:44Z")
> [@1010011010](#): > > Did the enemy boats catch fire at a temperature less than ~6000K? > > It’s a heat transfer question. You have a hot rock. How do you heat something until it’s hotter than your heat source? You don’t. You can’t. No matter how many hot rocks you use. That only works for convection and conduction. With radiation, the temperature of the object rises (or falls) until energy in equals energy out. ---
**Author:** ![Gary\_Robson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gary_robson/32/3448_2.png) [@Gary\_Robson](https://boards.straightdope.com/u/Gary_Robson)\ **Post date:** [November 26, 2008, 10:38pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/39 "2008-11-26T22:38:21Z")
Getting back to the OP, people who work in the TV business may still have a use for them. When converted to digital (yes, the “aimable” dishes can be wired for digital), they operate without that damned delay the small dishes have. Have you ever noticed that closed-captioning seems to lag the audio so much more than it used to? It’s because much of the realtime captioning is done from homes, and the captioners are using small dishes (e.g. Dish Network or DirecTV) instead of the big ones. ---
**Author:** ![1010011010](https://avatars.discourse-cdn.com/v4/letter/1/ea666f/32.png) [@1010011010](https://boards.straightdope.com/u/1010011010)\ **Post date:** [November 26, 2008, 10:54pm UTC](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486/40 "2008-11-26T22:54:51Z")
> [@Sunspace](#): > > That only works for convection and conduction. With radiation, the temperature of the object rises (or falls) until energy in equals energy out. You end up with two 6000K black bodies: the sun and whatever object you’re pointing your solar collector at. In practice, the sun isn’t actually an ideal blackbody, neither is the target, the target will shed energy faster than by black-body radiation alone and will not reach 6000K. IIRC the largest solar furnace in France peaks around 4000K. [Previous page](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486.md?page=1) [Next page](https://boards.straightdope.com/t/why-do-some-people-still-have-those-big-ass-satelite-dishes-in-their-backyard/474486.md?page=3)