You are all wrong and spinning your wheels....ThomasRz had the correct answer and you blew past it for 1 1/2 pages of wrong info.
Satellite Radio Can Do It.....Why Not Dish
- Thread starter Musky boy
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if you are talking about his answer of there being terrestrial repeaters.... then you are wrong.
those repeaters only work in major metro areas. The closet XM repeater to where I live is about 200 miles away. I pick up the signal from the satellites in the sky. And yes I know that for a fact, cause there are two different signal meters on the reciever.
The reason is a combination of many already brought up on here.
For one they both use multiple satellites to broadcast the signal conus so that no matter where you are at and which direction you are facing, you should be able to pick up a signal. Also, Sirius has 3 satellites flying in a figure 8 so that at any one time there are 2 of the satellites over the US and 1 over mexico making the lower part of the figure 8.
Secondly, it takes a whole lot less bandwidth to transmit audio only than it does to transmit video and audio.
Antenna Differences are bandwidth and power related
Wow, its been way too long since I took antenna theory but here goes. Antenna size and shape are related to power sent and received and bandwidth. For example in the early 70s the average bit rate of a interspace satellite was around 90 bits per second; thats right 90 bits per second. This was due to the signal to noise ratio of the receiver, the power from the satellite and the antenna size. Today's satellites are in the megabit range due to the significant increase in power output of the satellite, the larger antenna on the satellite and the significant increase in effeciency of the receiver on the ground, ie the reduction in the noise floor of the reciever so the signal to noise ratio is better by a factor of at least 100 or better; just a guess here but its significant.
So what does that have to do with XM or Sirius and Dish? Well, the average bandwidth of the signals from the satellite radio satellites are about 150kbits and the power is significantly greater, whereas the Dish satellite bandwidth per signal is around 1 meg or greater depending on the type of signal ie SD vs HD and the power is much lower given Dish is trying to send maybe 100 channels per satellite. So if power is lower, bandwidth is higher for Video and bandwidth is lower and signal is stronger for radio then the antennas need to be larger to capture the same amount of signal for video vs the signal for radio.
Hope this makes sense. One more thing; becuase the bandwidth is higher for video, the signal to noise issue raises its ugly head. The wider the bandwidth the more noise so the more signal that is needed to receive a detectable video signal. So you either increase the signal, make the antenna larger or do both to achieve a balance that is acceptable. Thats why the old c band antennas were so big.
I have left out a lot but I hope I helped a little. Also I am sure I may have some of my facts off such as bandwidth and such but the principles I have tried to lay out are factual.
John
Wow, its been way too long since I took antenna theory but here goes. Antenna size and shape are related to power sent and received and bandwidth. For example in the early 70s the average bit rate of a interspace satellite was around 90 bits per second; thats right 90 bits per second. This was due to the signal to noise ratio of the receiver, the power from the satellite and the antenna size. Today's satellites are in the megabit range due to the significant increase in power output of the satellite, the larger antenna on the satellite and the significant increase in effeciency of the receiver on the ground, ie the reduction in the noise floor of the reciever so the signal to noise ratio is better by a factor of at least 100 or better; just a guess here but its significant.
So what does that have to do with XM or Sirius and Dish? Well, the average bandwidth of the signals from the satellite radio satellites are about 150kbits and the power is significantly greater, whereas the Dish satellite bandwidth per signal is around 1 meg or greater depending on the type of signal ie SD vs HD and the power is much lower given Dish is trying to send maybe 100 channels per satellite. So if power is lower, bandwidth is higher for Video and bandwidth is lower and signal is stronger for radio then the antennas need to be larger to capture the same amount of signal for video vs the signal for radio.
Hope this makes sense. One more thing; becuase the bandwidth is higher for video, the signal to noise issue raises its ugly head. The wider the bandwidth the more noise so the more signal that is needed to receive a detectable video signal. So you either increase the signal, make the antenna larger or do both to achieve a balance that is acceptable. Thats why the old c band antennas were so big.
I have left out a lot but I hope I helped a little. Also I am sure I may have some of my facts off such as bandwidth and such but the principles I have tried to lay out are factual.
John
Musky Boy
Although there are a lot of posts with info, I believe the link posted by "randomq" will give you a pretty good answer to your question. Even though there are a lot of characteristics of a signal, the bottom line, "it's the signal" and the equipment used to process it.
As stated/suggested/suspected, an omni-directional antenna would not work (well) with a DBS system using multiple satellites that all use the same frequencies in the same geographic area (i.e., using non-spotbeam). Similarly, a Sirius/XM type system would not work with a single dish (directional) antenna, where the quality of the signal depended on multiple signals from satellites in different locations.
I've used Frequency Diversity, Time Diversity, and even Space Diversity with receiving antenna's, but never gave it much thought about using Spatial Diversity on the transmitting side. But then those at the bottom of the western Rockies could pick up the PI channels from 148 while those on the east could get it from 61.5.
EDIT:
Next "Mad Project" -- Point a single dish at 148 and one at 61.5, mix the two signals with a 50 - 2150 MHz splitter, and feed into a Dish receiver and see if it gets confused.
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No one ever said it doesnt take less bandwidth to transmit audio...however, the ground based fill in at the metropolitian areas are why you can get the signal in these areas where the bulk of the population lives.
You really arent going to tell me you believe that the satellite radio works in a house or office with no view of the sky and its because of the audio needing less bandwidth are you?
If D* or E* were allowed ground based repeaters they could essentially do the same thing.
Sirius bandwidth
As I stated earlier in my reply I wasnt sure about my numbers but I was tryng to make the point about the relative bandwidth issue.
I have found a quote from an article about bandwidth which I am including below. It is from an article about a Sirius receiver which can be found at:
http://www.hometheatermag.com/accessories/706antex/
To fit more than 125 stereo audio channels into a satellite bandwidth of 12.5 megahertz—roughly the amount of two digital or analog television channels—Sirius uses a PAC (perceptual audio coder) developed by Lucent. It supports data rates ranging from 1.41 mega-
bits per second down to 24 kilobits per second. To my ears, it sounds like MP3 files at somewhere between 128 and 160 kbps.
Dont know if this helps but it is close to what I estimated.
As I stated earlier in my reply I wasnt sure about my numbers but I was tryng to make the point about the relative bandwidth issue.
I have found a quote from an article about bandwidth which I am including below. It is from an article about a Sirius receiver which can be found at:
http://www.hometheatermag.com/accessories/706antex/
To fit more than 125 stereo audio channels into a satellite bandwidth of 12.5 megahertz—roughly the amount of two digital or analog television channels—Sirius uses a PAC (perceptual audio coder) developed by Lucent. It supports data rates ranging from 1.41 mega-
bits per second down to 24 kilobits per second. To my ears, it sounds like MP3 files at somewhere between 128 and 160 kbps.
Dont know if this helps but it is close to what I estimated.
Absolutely... I did an car install inside a shop building on Friday night. Turned the key on and guess what? 1 bar of Sirius signal. I even activated the radio with the vehicle in the building! We don't have any repeaters near us at all. You can also verify it against the signal meter with it saying zero on the "TER" signal and 1 bar on the "SAT" signal meter. We were so far out in BFE that you can't get DSL, Cable TV, Cable modem, and even zero cell phone service let alone a Sirius satellite repeater.
I can get a signal inside of my building that I work at, if I set the antenna right next to the metal wall. And I gaurantee that I am no where near a repeater. I wish like hell I was, cause driving through town (with tall buildings) is a pain as the signal drops in and out.
The use of signal repeaters has NOTHING to do with satellite reception out in the middle of nowhere. Thats like saying because New York puts out their local channels out OTA, it helps my satellite receiver at home pick up those channels. Two completely different things.
The use of signal repeaters has NOTHING to do with satellite reception out in the middle of nowhere. Thats like saying because New York puts out their local channels out OTA, it helps my satellite receiver at home pick up those channels. Two completely different things.
Here is a graphic of both Sirius & XM sats & coverage maps. You can also use a sat. dish to increase the signal strength for XM's fixed sats. the 4th pic is such a setup from Costa Rica receiving XM, you need to aim the dish at XM's sats for this to work
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Thanks guys. I learned a lot. Mostly learned that this technology is a bit over my head, but seems that it would be possible to use an omni directional antenna if the satellites had enough power.....maybe in the future. Sounds great that xm and sirius have looked into this already.
Musky boy
Musky boy
Actually no, the DBS companies wouldn't be able to use an omni antenna. That would be like basically limiting them to one slot up in the sky.
there are alternative satellite antennas out there. flat panel type antennas, little dome shaped ones. mostly used for use on top of cars, rv's, boats, ect.
and they work just fine, they just have moving parts inside that keep themselves lined up.
so if you really wanted a smaller dish to pick up your dbs system, you could, but they arent cheap
