xm vs sirius

I think there are a lot of variables here. One is the antenna and its placement. Also the route while driving (ie, anything to block the signal).

I have a Pioneer portable XM in my Prius and the reception is great, but if I had a Sirius system in, I'd be surprised if it wasn't as good.

 

I've heard that XM has better reception....

But I'd never get Sirius as long as XM has Opie and Anthony...

 

Let's talk about the technology before the content.

Both use 2.3 GHz
Both use LOSSY compression to transmit data

XM uses the HE-AAC (Advanced Audio Coding), which heeds compression in the range of 32-48kbits/s.
XM uses two Boeing 702 satellites - providing 3 kWatts of RF radiation in a geostationary orbit.
If you do not have a good view of the southern sky, reception is less than perfect. XM has tons of ground repeaters because of this 'bug.'

Sirius uses PAC (Perceptual Audio Coding), which heeds variable compression from 8-64 kbit/s.
Sirius uses three Loral FS1300 satellite - providing 10 kWatts of RF radiation in an elliptical orbit. This reduces the number of ground repeaters needed.

It could be that you are in an area with a lot of interference and it just happens that XM has a ground repeater near by.

Technically, Sirius has _far_ better fidelity when compared to XM.



IMHO, XM is horrible. When I have heard it in a car, it sounded like a really cheap MP3 playing because the bit rate was so poor.
XM also has fewer channels than what I would listen to. They have a lot of rap and crap, but nothing with real meaning or quality.

Sirius is quite nice. I've heard it in several cars and never once did I hear any distortion due to compression. The available selections are great; NPR, Bluegrass, lots of electronic and dance music. The list goes on.

 

Well, this is a bit of an unfair generalization. XM and Sirius content match up very well. Looking at my XM 130 channel guide I see individual channels for 40s through 90s music, country (including bluegrass) pop, rock, hip hop, jazz, blues, dance, Latin, world, classical, kids, news (such as CNN, ABC), comedy, talk, entertainment (including MTV, VH1, books) and sports (with ESPN, Fox, MLB. NASCAR, college football).

Of course, there may be specific channels that tip the scales for someone, personally I like The Loft and XM Cafe on XM, and chose it partly based on those channels.

fd

 

I had a Delphi XM MyFi for a while last year. I could put the antenna on my dashboard and get acceptable reception. When I got rid of XM and got Sirius I had to mount the antenna on the roof of the car. Even then, it still cuts out when driving between tall buildings or other obstructions.

I attribute the superior reception of XM to the number of ground repeaters in my area. I could get reception indoors at home and in my office at work with XM, and can't get a thing with Sirius. That has to be due to the repeaters. But I like the programming better on Sirius, so that was my choice.

 

XM does not have a single NPR station. Nor does it have Canadian Broadcasting (CBC). Nor Public Radio International.
It only has four dance stations and only one is worth listening to.

The last thing that I want to see on any programming guide is NASCAR; a 'sport' originating from the illegal acts of bootleggers... But that's another whole thread.

Back to original post...

The poor reception is most likely to do with the location where your receiver is placed and the amount of near by interference. Your friend with the XM is probably just picking up reception from the ground repeaters.

Try placing the receiver in the middle of your dash where it has the most direct view of the sky.

If that does not solve the issue, then you might have a faulty radio in your portable unit.

The Sirius satellites have continuous coverage of the United States, similar to the way the
Russian spy satellites used to [still?] work.
Sirius satellites
® Spaceflightnow

So you should have reception no matter what.

 

I have the Factory Interactive Sirius kit, I put the antenna in the center of the roof right behind the factory FM antenna. I also had it off to the drivers side at one point where Factory Interactive recommends.

In both placements, I get good reception. However, driving under overpasses I do get signal loss for a few moments. It is rather annoying.

Is this common / expected? Would a different antenna work better (FI says they provide a different antenna that is supposed to be better) or is this more of a problem with the tuner?

Ken

 

I don't know how much of this is speculation, but I've heard rumors that Sirius is going to be running on a somewhat commercialize format (like standard radio) due to advertising contracts with Howard Stern. With his salary at 500 million over 5 years and around 1.8 million subscribers, Sirius may find it hard to pay some bills.

 

I'm sold on Sirius partly because my wife already has a subscription. I'm nervous now about the reception. Does anyone have experience with the "factory" Prius install? My wife has a Lexus LX470 with the factory Sirius and I have never heard it even hiccup. If the factory interactive cuts out under overpasses that would drive me nuts.

Hopefully taking delivery of my new 06 tonight!

 

It's somewhat expected if you spend more than about four seconds under the overpass.

There is a buffer in the receiving unit that should store up to 4 (possibly more) seconds of data. If you are spending more than the buffer length under the overpass, then the data stream is interrupted.

As an experiment to see just how large your buffer is... Get a handful of foil and make sure it will cover the antenna completely.
Turn on your radio and listen to a station for about 12 seconds. Then, place the foil (or your hands) over the antenna and count how long it took for the radio to stop playing. This should give you an idea how much data is buffered.

The buffer size is also dependent on the receiver manufacturer. Some receivers have a "pause" function that allows the data to be stored up to 50 seconds or more...

Maybe. A different antenna just yields a different 'gain.' The different antenna would just have a larger surface area.

You could always strap one of these bad boys on the top of the car...
[Broken External Image]:http://www.hyperlinktech.com/web/copyrighted_images/hg2414p_400.jpg
(2.3 GHz WCS antenna)

 

It all comes down to content. If you're a football fan get Sirius and the football package. If you're a baseball fan get XM. If you're an Howard Stern fan get Sirius. If you like Opie and Anthony get XM, etc. etc. etc.

 

I agree. I live on Long Island and have had the opportunity to own both. I had Sirius in my Jeep Liberty and now have XM in my Prius. I am FAR from an audiophile (how can you with the crappy JBL stereo) and would never,ever hear the difference between the two even if I tried. I hate Howard Stern (his humor is so old already). I am very pleased with the channel content of XM. I can drive under the GWB and long underpasses and apparently there must be repeaters as there is no pause. XM is cheaper too.

 

Reception depends on antenna placement and the number of ground repeaters in your area. For a detailed discussion visit the Sirius and XM forums where this topic has been beat to death.

/I subscribe to Sirius and get excellent reception.

 

The Sirius satellites are higher above the horizon than XM's. So if you are in a metropolitan area, like New York City e.g., and driving down Park Ave., the tall buildings on both sides of you would be less likely to block out the signal. So that's a consideration if you are in a city with tall buildings.

 

No. Sirius is expecting to and will probably get higher ad rates on the non music channels where they currently run ads. The music channels have always been commerical free, XM stated out with limited commericals on the music channels and then switched.

 

I get drop outs going under overpasses at 40-50 mph, no where near 4 seconds.

I do know it has a little buffer, maybe a few seconds, when I pull into the garage it stays on for a couple seconds.

I'm thinking that this unit just has a small buffer and it's part of the issue. This is the Factory tuner, someone was asking. FactoryInteractive sells the Toyota tuner part.

My wife has an XACT Replay tuner, which does have the replay feature. I haven't used hers on the road like I do mine though to compare the drop out difference. I'm starting to think though that it's the tuner and I may be regretting going with the factory integration versus the features. The external tuners get you a lot more features than you get with the factory setup....

Ken

 

I have XM and am really happy with it. Clearly I'm not an audiophile, because I think the sound quality is good and am extremely happy with the selection of music. Personally, I like Punk/SKA. Fungus 53 is fantastic and alone is worth the cost to me. There is no comparison to Faction on Sirius that adds Hip Hop to the Punk/SKA channel. No thanks!
I also wish XM had NPR. The XMPR channel isn't very good.
Does Sirius have an exclusive contract with NPR?
A friend of mine has Sirius and the NPR channels sound awful. He asked Sirius and was told that is what NPR is giving them. Can someone with Sirius confirm the poor sounding NPR?
I've just been podcasting my NPR needs or actually using the FM radio to listen to NPR.

I live close to Philadelphia, there must be a number of XM repeaters around here, because I can be sitting in traffic on 676 under an overpass and still have perfect reception.

 

Just reading that it isn't clear how any amount of buffering could prevent signal interruption. Once the signal is lost, it's lost forever. The reason it does work is because Sirius employs temporal diversity, or a delay between the satellite signals. One satellite is broadcasting data four seconds behind the other, so if the interruption is short enough, the receiver can switch to the delayed signal, use that for the data lost from the "leading" satellite, and avoid an interruption.

 

I have an XM radio, and I've noticed the phenomenon that if I drive under a bridge without stopping, then no signal loss, but if I stop under the bridge for more than a second or so, then the signal drops out.

I assumed they accomplished that through error correction redundancy in the data. There are many algorithms for error correction in digital transmissions that use additional (redundant) data in the stream, along with temporal spreading of the signal.

Say the following string of letters represents a stream of audio, with each different letter representing a different second in the stream. For instance, the five a's represent the 1st second, the five b's represent the 2nd second, etc.

aaaaabbbbbcccccdddddeeeeefffff

You can add redundant information into the data stream that would allow you to lose any one of the five blocks that make up a second of audio and recreate the missing data from the redundant data. However, if you lose two or more of the five blocks in one second, then you can't recreate the missing data. (ex. if you lose two c's in the above example string)

You can enhance this error correction algorithm by spreading the data in time. The following example shows interleaving each second of audio with the previous and next seconds of audio.

(This looks better with a fixed space font)
The following temporal spreading of each second of data...

a_a_a_a_a______________________________
_____b_b_b_b_b_________________________
__________c_c_c_c_c____________________
_______________d_d_d_d_d_______________
____________________e_e_e_e_e__________
_________________________f_f_f_f_f_____
______________________________g_g_g_g_g

yields the following data stream...

a_a_abababcbcbcdcdcdededefefefgfgfg_g_g

With this scheme you can lose two consecutive blocks and know that you can recreate them both. For instance, if you drive under a bridge, you might lose two consecutive data blocks such as one of the 'de' pairs from the middle of the example string. Even though you lost two consecutive blocks, they are guaranteed to come from two different seconds of audio, and therefore you only lost one block from each of the seconds and can recreate them both.

I would expect that based on my observation of XM, they use some scheme along these lines. It could be that Sirius uses a less robust error correction scheme or none at all. (None at all would be hard to believe)