Reception in general

[mmcdelray]

Here are some reception questions and rambling notes, all pretty trivial but possibly of some interest to techie types.

a. Q for anyone: Re reception, when using XM in the car and the signal is blocked by a bridge or mountain, and once the signal is recaptured, why is there then a dead echo? Seems like there is some sort of time shift delay in the reception, but not being a satellite junkie, it's not clear to me why this happens. Just curious.

b. Note: I drove up to Nova Scotia and Newfoundland last month and took along the XM. I had earlier asked XM tech support how far across the border did the signal stretch in the northeast, but I only got a standard legal line of 50 miles and everything complies with international broadcast rules etc. Anyway I got a strong signal clear across New Brunswick, Nova Scotia and out to Cape Breton. Only when we got to southern Newfoundland did the signal start to flutter; interestingly, it was ok at the lower channels and nil at the higher channels (anything above On Broadway, I think that's 23 or so), why?? As I drove further north and east, the limited reception then dwindled further. By the time I got to St. John's, I could barely bring in the preview channel on 4. Don't know if the limiting factor was the northerly or the easterly stretch, I think it was the latter.

C. Q's Just wondering...Does anyone have a footprint map of the XM satellite reception area and of the active repeater nodes? Also, what is the USB port on the Sony intended for??

D. General reaction...we have Xm for about half a year now, great reception and quality here in S Florida, listen in both home and car with Sony pnp model...Main gripe is the frequency of Xm promo's on the commercial stations. You have to wonder if these will flip over to paid advertising once the listener base hits some magic number, who knows when. Main concern is whether their positive cash flow point will happen soon enough to prevent them from burning through all the investment capital with what appears to be a hefty monthly operating overhead; meanwhile let's enjoy the good service.

[Scott Greczkowski]

what is the USB port on the Sony intended for??

All excellent questions, and I would love the answer to the above myself. Calls to Sony tell me that the XM USB kit is not available "yet"

So it appears its coming, but the question is what does it do?

[RJS1111111]

"Only when we got to southern Newfoundland did the signal start to flutter; interestingly, it was ok at the lower channels and nil at the higher channels (anything above On Broadway, I think that's 23 or so), why??"

Not having any detailed knowledge about satellite radio, I could venture a couple of guesses... :)

Higher channels might be at slightly higher frequencies (different transponder, unless XM uses only one transponder). Losses may be higher through the atmosphere, through your car window, and/or within your radio. The proposed higher transponder might even actually have a weaker signal. I imagine that it's frequently foggy, rainy, and/or drizzly in Atlantic Canada. This might tend to affect a higher frequency first.

Also, higher frequencies give a more focused beam, so perhaps the higher channels fall off more rapidly at the beam edges.

Of course, you realize you're getting a useful signal, way outside the XM supposed range. Don't let the Mounties hear you listening to a foreign US signal. It could be against Canadian law now! You should wait until Canada has its own satellite radio, and get a different receiver for use when traveling in Canada. (Just kidding, I hope.) ;)

"a. Q for anyone: Re reception, when using XM in the car and the signal is blocked by a bridge or mountain, and once the signal is recaptured, why is there then a dead echo? Seems like there is some sort of time shift delay in the reception, but not being a satellite junkie, it's not clear to me why this happens. Just curious."

The audio channel is actually a digital data stream, which is buffered by your radio, so when the signal is lost and re-established, the buffer is at least partially emptied, and you have to wait for it to fill up again, before you hear anything new.

[HornHonker]

Here is a link to the XM footprints.

http://www.oz.net/~keitht/footprint.htm

[Scott Greczkowski]

Great Link Horn Honker thanks! And Welcome :wave:

[NedDorsey]

Originally posted by HornHonker
Here is a link to the XM footprints.

http://www.oz.net/~keitht/footprint.htm

From the footprints it appears the satellites are not directly above the equator? I thought they were, since I think I've read something about being able to see the southern sky. Or are they using spot beams pointed at roughly Seattle and NYC?:shrug:

[RJS1111111]

Those footprints look like very typical shaped CONUS beams to me. Most likely they're at the equator, too, given that they have
fixed longitudes.

[NedDorsey]

Originally posted by RJS1111111
Those footprints look like very typical shaped CONUS beams to me...

:confused: What's the difference between a CONUS beam and a spot beam? Wider and more oblong?

[BuggyBoyWA]

CONUS is a transponder that is intended to be received throughout the CONtinental United States. A "spot-beam" is a transponder (one frequency transmitter) that focused upon a small area. For instance, DirecTV uses spot-beams to reuse 6 frequencies across all locals on their 101 satellite, DirecTV 4-S. Seattle, Portland, Sacramento, San Francisco, Los Angeles (X2), Houston, Dallas DMA's, etc all have their own spot-beams to reuse the same frequencies in other areas of the country. Much like FM radio stations broadcast in different areas on the ground, this is just from a satellite instead.

[BuggyBoyWA]

If you want to see a map of the DirecTV 4-S spot-beams, go here: http://www.scottandmichelle.net/scott/dtv.html

This was a project that barclay from the TiVo Community started.

[NedDorsey]

Thanks for the information and links. It makes sense now.

[dlsnyder]

It looks like New Orleans would get the same signal strength as that found in Newfoundland. Is that the case or is the signal strength contour a little bit off there?