Satellite radio defying all natural laws

[The Kernel]

Alright, so I have noticed something over the last few weeks which seems to defy any explanation whatsoever. I'm hoping someone here can figure this out, because I sure can't make any sense of it.

Background: I bought a new car earlier this year (Lexus IS350 if that matters) and I decided to spring for the factory installed XM radio option. XM radio as many people already know functions by receiving broadcasts from geostationary satellites and is strictly line-of-site, which means that it doesn't function unless it has a relatively clear view of the sky. I have noticed (as many people have) that the broadcast tends to cut out when I go underneath overpasses or even large trees for any significant period of time (there is a small amount of buffering, but it cuts out pretty quickly).

Now here is the thing I need resolved. I live in an apartment complex with underground parking that completely covers the sky and has no view of the sky whatsoever (it's completely underground with two floors of concrete between me and ground level). Yet wherever I am in the parking garage, my XM radio works like a charm. No cutout, no signal loss, just perfectly clear reception no matter where I am in the garage. This is not due to buffering (as it works the second I start up my car with no problems and will continue working for any amount of time I am stationary underground) and I can't find a rational explanation for this. Heck, even my terrestrial radio doesn't work in the garage (it is nearly completely engulfed in static), yet the satellite radio works perfectly.

Can anyone come up with an explanation for this?

[Bounty]

Terrestrial repeaters? Maybe for some reason someone is rebroadcasting the signal inside your building... or you garage. Can't imagine why you'd need radio wile parking through.

[The Kernel]

Terrestrial repeaters? Maybe for some reason someone is rebroadcasting the signal inside your building... or you garage. Can't imagine why you'd need radio wile parking through.

Doubtful because the trees right outside my parking garage interfere with the signal just fine.

[Feil]

Not an answer, but a potentially useful observation: XM "radio" operates in the low infrared range, just under the level where our atmosphere goes mostly opaque to IR. Normal long-wave FM radio operates in the radio band, at a much larger wavelength.

[Mr Bean]

XM has some ground side repeaters in some areas. I suspect for whatever reason your apartment complex has one. They are short range and designed to cover areas like major tunnels and some underground parking garages. I know the shops in DC had them.

[The Kernel]

XM has some ground side repeaters in some areas. I suspect for whatever reason your apartment complex has one. They are short range and designed to cover areas like major tunnels and some underground parking garages. I know the shops in DC had them.

In major metropolitan areas I guess I could see that...but in a small private apartment complex in Mountain View, CA? Seems like a strange place to put a repeater unless some XM radio executive lives here.

[Sea Skimmer]

The frequencies are completely different for terrestrial radio stations vs. satellite radio. AM radio is roughly is 500kHz-1,600kHz, FM radio is roughly 85-110MHz while satellite radio is at around 2,300MHz, similar to cell phones and wireless network routers. In addition satellite radio is all digital, it can either work or not work, while most broadcast radio is still analog and thus inherently subject to loss of information. This makes digital signals a lot more robust.

The high frequency direct wave system used by satellite radio is actually less effective at penetrating cover then the lower broadcast frequencies. However concrete in buildings doesn’t do that much to block radio signals, steel bridges will create much more interferences with much less thickness. A couple concrete floors don’t really amount to all that much material. A radio signal coming down from a satellite overhead is going to encounter less material then a signal from a radio tower that has to hit that underground parking lot at a slant angle, which would force the radio waves to penetrate the ground. I addition satellite radio also actually uses a large number of ground repeater stations in the US to improve coverage because its completely line of sight, so its quite possibly you live near one of those repeaters. I don’t know about trees, the water in them can block radio waves sure, but it would have to be an awful lot of tree cover for that to matter.

It’s also possible that your simply getting interference from something in certain areas, maybe your car ignition, though I’m not sure that can affect 2.3Ghz the way it can lower frequencies.

[The Kernel]

The frequencies are completely different for terrestrial radio stations vs. satellite radio. AM radio is roughly is 500kHz-1,600kHz, FM radio is roughly 85-110MHz while satellite radio is at around 2,300MHz, similar to cell phones and wireless network routers. In addition satellite radio is all digital, it can either work or not work, while most broadcast radio is still analog and thus inherently subject to loss of information. This makes digital signals a lot more robust.

The high frequency direct wave system used by satellite radio is actually less effective at penetrating cover then the lower broadcast frequencies. However concrete in buildings doesn’t do that much to block radio signals, steel bridges will create much more interferences with much less thickness. A couple concrete floors don’t really amount to all that much material. A radio signal coming down from a satellite overhead is going to encounter less material then a signal from a radio tower that has to hit that underground parking lot at a slant angle, which would force the radio waves to penetrate the ground. I addition satellite radio also actually uses a large number of ground repeater stations in the US to improve coverage because its completely line of sight, so its quite possibly you live near one of those repeaters. I don’t know about trees, the water in them can block radio waves sure, but it would have to be an awful lot of tree cover for that to matter.

Trust me on this part, I've used the system enough to know what causes interference for it. Trees and even overpasses cause interruptions and you don't even need that much tree cover to do it. Like I said, the tree cover outside my apartment causes sporadic outages, and it isn't even that thick...



I've also taken my car driving in heavily forested areas and the amount of dropoff is consistent with the tree coverage. Also going into any other parking garage causes total signal loss with zero exceptions aside from my apartment parking garage.

The repeater idea makes some sense, although I still don't see why the repeater would work underground and not as far as the trees 15 feet from my garage entrance.

[Bounty]

Maybe the garage is at the extreme edge of a repeater's range?

[The Kernel]

Maybe the garage is at the extreme edge of a repeater's range?

Possibly, but since the repeaters work on the same principles as the satellite broadcasts, wouldn't they be limited by the same line-of-sight? If so, the repeater would have to be inside the garage, which while possible seems like a huge waste.

[Sea Skimmer]

Possibly, but since the repeaters work on the same principles as the satellite broadcasts, wouldn't they be limited by the same line-of-sight? If so, the repeater would have to be inside the garage, which while possible seems like a huge waste.

The smallest repeaters cost like 100 bucks, and can be purchased for home use specifically for dealing with rooms that have poor reception. It is entirely possible, indeed probable given how big it looks to be, that your building has one, or more likely two, one for each XM and Sirus.

[Superman]

By the way, XM is now "Sirius/XM." Now you too can enjoy the sheer radio bliss known as The Howard Stern Show, complete with George Takei announcing.

I've never really had any signal problems with mine. It works in parking structures, car washes... all sorts of odd places. I dunno, but I think the antenna is supposed to attract the signal via a magnet, right? Maybe the signal bounces of the walls.