Satellite Radio Can Do It.....Why Not Dish

[Musky boy]

Why is it that I need a dish to watch Satellite tv........but I can get Satellite radio without a dish?.......I just need a small antenna.

John

 

[cybertrip]

That is a really good question. The most logical answer I could find is that Satellite Radio puts out more power and uses higher gain antennas than Satellite TV. All of the Satellite Radio channels are equal to about one Sat TV channel. Therefore they can use more power for that single transponder rather having to distribute the power amongst several transponders thus making the signal stronger to you and easier to pick up on such a small antenna. The beamwidth is the same for both Sat Radio and TV however, it's the gain and power being sent to you that makes a difference. A parabolic dish allows you to focus a signal better thus increasing the gain of your signal. If you used a monopole (sat radio) antenna to pick up your TV signals you would have almost no signal.

Honestly though, unless I see an answer from the engineers of Sirius or XM I can't say exactly why that is. But from my experience with RF I would say that the Satellite Radio satellites are probably putting out more power and using higher gain.

 

[SmityWhity]

I haven't did any research to see how satellite radio works, but here is something else to consider.

Direct Broadcase Satellite Service (DBS) generally uses satellites operating in the KU band, from 12.2GHz - 12.7GHz on 32 pre-defined frequencies, i.e., one for each of the 32 transponders.

So Dish Network provides DBS service to the U.S. from several satellites at 61.5, 110, 119, 129, and 148 degrees. Generally, each satellite is using the same frequencies (and polarity). These satellites are using higher power than the other satellite systems, therefore, a smaller dish such as the 18" dish can be used.

But this dish antenna is also serving as a direction antenna, without it, you would be attempting to pick up signals from all 5 satellites at the same time, and this is not including the satellites from the other service provider (DirecTV). It would be like being half-way between 2 regular TV stations both operating on Channel 5.

 

[ThomasRz]

Why is it that I need a dish to watch Satellite tv........but I can get Satellite radio without a dish?.......I just need a small antenna.

John

Satellite Radio has terrestial repeaters in major metro areas otherwise you would not have reception in buildings.

 

[cybertrip]

I haven't did any research to see how satellite radio works, but here is something else to consider.

Direct Broadcase Satellite Service (DBS) generally uses satellites operating in the KU band, from 12.2GHz - 12.7GHz on 32 pre-defined frequencies, i.e., one for each of the 32 transponders.

So Dish Network provides DBS service to the U.S. from several satellites at 61.5, 110, 119, 129, and 148 degrees. Generally, each satellite is using the same frequencies (and polarity). These satellites are using higher power than the other satellite systems, therefore, a smaller dish such as the 18" dish can be used.

But this dish antenna is also serving as a direction antenna, without it, you would be attempting to pick up signals from all 5 satellites at the same time, and this is not including the satellites from the other service provider (DirecTV). It would be like being half-way between 2 regular TV stations both operating on Channel 5.

XM and Sirius have satellites in different positions as well. Sirius actually has orbiting satellites. Think of it like GPS. They all have small antennas yet they pick up several satellites. A satellite dish is directional, that's why it has greater gain. Without the reflector (dish) you would be picking up all sorts of noise and interferance. As far as metro repeaters, let's take that out of the loop, although a cool idea because I drove through a tunnel in LA and I still had radio. I live in a rural area where repeaters don't come in to play. The radio wavelength of a XM signal vs a DBS signal is going to be the same. They both use Ku band satellite signals. Therefore you should in theory be able to pick up an XM signal and a DBS signal with the same puck antenna, right? Well, that depends on the signal output of the transponder and the gain of the antenna for that transponder. My guess as I said before is that XM/Sirius use higher gain satellites and produce a higher output power. Hmm, now what would happen if I hooked up a puck antenna... or built a dipole antenna for Ku band and hooked a pre-amp to it. I guess that's a weekend project to do. I can't imagine that the signal would be strong enough for a video signal to come through. Maybe some low bitrate audio, such as satellite radio, but with all the data that comes through video I wouldn't have a good enough signal to even start to decode that data. This is another reason why it won't work.

So thinking about it more. Satellite radio transponders and Sat TV transponders could have the same physical specs for the antenna gain and for the power output. But since there is less data being sent over for a audio signal than for a video/high bitrate audio signal you could decode it easier without having to have it resent several times to do error correction. I think I figured it out.

 

[photoman76]

XM and Sirius use S Band not Ku band. XM frequencies are 2332.5 MHz through 2345 MHz. Sirius frequencies are 2320 MHz through 2332.5 MHz.

 

[Van]

Sure they ar both tree's but when it comes down to it your comparing apples and oranges and lemons if you throw in gps.

 

[Fredinva]

re Sirius orbiting birds

cybertrip,

As I understand the Clark belt, all satellites are orbiting - geosynchronously.

fred

 

[Neutron]

Sirius's satellites orbit in a "Figure-8" pattern.

 

[sullivbt]

The XM satellites are the most powerful (in terms of emitted power, dbW, from the transponder) birds ever put into orbit. The hugely powerful (relative to the low power DBS sats) signal and the S-band frequencies (which are less affected by iono attenuation) allow the sat radio signal to be recieved on earth with very small antennas. In no way, shape or from could DBS signals EVER be recieved by antennas similar in size to sat radios.

Fredinva: satellites can be placed in any orbit that we want to put them in. The only thing special about geosynchronous (technically known as geostationary) orbits is that sats in that particular orbit move at the same velocity as does the earth. As neutron points out, Sirius actually uses 3 sats orbiting in a figure-8 pattern - they are, obvioulsy enough, NOT geostationary . XM, however, uses 2 sats that are geostationary. Some people claim that XM offers better reception in CONUS than does Sirius due to that fact - I have no particular experience with Sirius so I will not comment.

 

[navychop]

A geostationary orbit (GEO) is a geosynchronous orbit directly above the Earth's equator (0º latitude). From the ground, a geostationary object appears motionless in the sky.

A geosynchronous satellite is a satellite whose orbital track on the Earth repeats regularly over points on the Earth over time. If such a satellite's orbit lies over the equator, it is called a geostationary satellite.

From Wiki.

 

[sullivbt]

Alright, let me try this one more time - that's the last time I post right before lunch when my blood sugar is low

XM sats are geostationary, alogn with the vast majority of communication sats in use. Geosynchronous and geostationary are not interchangeable - that is why I corrected the prior poster on the use of geostationary. "Geostationary" orbits are a subset of geosynchronous orbits, but, a snavychop points out, the distinction is that geostationary sats are always located at the equator.

 

[VinceT3]

It has something to do with the number of sats (like someone said about gps) and I also heard they are in a lower orbit which helps to with the pickup.. though I've never researched the validity of any of it..

 

[tomyo10]

also, why does my XM never go out in a rainstorm?

 

[icstephen]

I'm sure it has allot to do with FCC frequency allocation & bandwith also Audio uses far less bandwith than video so xm & sirius have a smaller slice of radio spectrum. I'm sure there will eventually be a service like this for video, Xm & Sirius had both talked at one time about having several video channels for your car (supposedly for the back seat tv's), I don't know what ever happened to that...but I sure don't want these clowns around here watching tv and driving (they can barely manage with out tv in their cars) . I would hope that we get a wifi type service some day.

 

[digiblur]

Some people claim that XM offers better reception in CONUS than does Sirius due to that fact - I have no particular experience with Sirius so I will not comment.

Sometimes... it depends on the area and installation. Say for instance you put the antenna out your office window and you get XM you'll get it no matter what time of day. Take a Sirius radio and do the same thing, you might lose coverage an hour later due to the movement of the satellites.

But in most cases you'll find the Sirius implementation to be better since XM has a very low "look" angle in the north. At some times of the day Sirius is straight up over your head.

Like I say it just all depends on your area..... I have Sirius and never have an issue with my car antenna or my boom box one. I just toss the boom box antenna out the window and call it done when I'm on a job. There are no repeaters in my area either.

 

[digiblur]

also, why does my XM never go out in a rainstorm?

The same reason C-Band satellite doesn't. The frequency.

 

[sullivbt]

Let me repeat what I said earlier - the number of sats and the alotted bandwidth have nothing to do with sat radio reception. Signal strength at the receiver (any sat receiver, for that mattter) is strictly a function of distance from sat and the transmitted power (in dbW), modified by some other factors (such as iono correction and "rain fade", which actually refers to the amount of moisture in the atmosphere and doe snot necessarily strictly pertain to "rain", per se).

 

[randomq]

Satellite Radio has terrestial repeaters in major metro areas otherwise you would not have reception in buildings.

Hmm, what frequencies does that operate on?

 

[randomq]

OK, just read a technical analysis of XM. They use a combination of extremely high power and a much lower symbol rate than typical FTA signals. The lower symbol rate makes noise much easier to filter out.

http://www.xmxp.com/forum/archive/index.php?t-39.html

Based on this, it would be interesting to try to receive very low symbol rate transmissions from a decently powered FTA satellite, using a Sirius/XM antenna. Of course, you'd have to find such a transmission on a frequency not used by other satellites, to avoid interference with your omnidirectional antenna.