Badger21

Just bought a 2014 Base AWD RDX and I'm having issues with XM cutting out after driving under an overpass. I can understand losing signal driving in a parking garage, but moving through an underpass at 40-50 MPH seems a bit much to completely lose signal. I bought the car full well knowing about the 2 second lag between changing songs and while I can deal with that, losing radio signal while stopped or driving under a bridge will get annoying quickly. Does anyone else have this issue?

barnowl

Anything that interrupts line of sight between the antenna and the sattelite will interrupt the signal.

I could put my hand over the antenna on my boat while working on it, and yup, the station would cut out.

Badger21

To be clear tho...this only happens when listening to XM. AM/FM transmissions are fine. From the little I know about radio broadcasting...this doesn't make a lick of sense.

Brown13

XM is a digital signal.If lost, it stops at the last point of signal.If You have cable and lose the signal,The picture freezes.Same with XM ,but no picture.
You lose the signal from the satellite when going through tunnels or overpass.So digital signal freezes for the time that it is lost.

RDX-Rick

There are several reasons to explain this.

As you know the XM signal arrives at your RDX via satellite, from over 30,000 KM away, while FM signals originate from ground based stations maybe 50 KM away. So the XM signals are usually going to be much weaker than an FM signal, and more easily attenuated by obstructions.

Since the XM signals arrive from above, while FM signals arrive horizontally from ground level, the XM signals will be blocked by overhead obstructions more often than FM signals.

Satellite communication works in the microwave region of the radio spectrum, while FM works in the VHF frequency range. The microwave XM signal behaves in the same manner as your microwave oven. In the MW oven, the radio waves are absorbed by moisture, and the water molecules get excited and cause the water to increase in temperature. In the same way, satellite signals are also absorbed by water, so passing passing under a thick tree canopy, or driving during rainfall will attenuate the signal even more.

Normally the XM receiver in your RDX has buffered a few seconds of the broadcast, and when the signal is lost, the receiver can continue to play without a noticeable break in the transmission. If you are not familiar with digital buffering, you can see it visually when watching a YouTube video. In YouTube you will see a red dot moving along the timeline to show your current position in the video. You will also see a thicker white line extending along the timeline that shows how much of the video has already been downloaded to your device. Often you can see the entire video has been downloaded while you have only viewed a small part of it. At this point you could turn off the Wi-Fi and still view the rest of the video.

So if you can get through that overpass in less than 2 seconds before the buffer has emptied, you won't notice any loss, but if it takes you longer than that, your signal will drop off for the time in excess of 2 seconds that you were under the overpass.

Badger21

Thank you all for the explanations. The buffer thing is interesting, have not had it save enough to where I was able to pick up where I left off. Frustrating for talk radio, but now I know why. Thanks again.

RDX-Rick

Well once again, it depends on how much time you are under the overpass. When I am driving at highway speeds I can pass under a bridge without any signal loss at all. When travelling under a similar sized bridge at slower city speeds, I will be under there long enough to deplete the buffer and I will miss part of the broadcast.