Quote:
Originally Posted by Electronic M
There were also practical reception issues. FM due to its shorter wavelength was prone to reflection cancellation. Regularly at lights I stop in a spot loose reception and have to creep forward a meter or 2 to try and recover reception....
|
"Stop light fade"
We looked at this problem for mobile digital TV, which suffers the same way because it's in the same frequency band. One interesting thing we found was that it's worse when the local buildings are tall compared to the width of the road - the signal reflects back and forth off the buildings, creating deep nulls. But it can hapen in more open areas too when there is a strong reflection that cancels out the main signal. EDIT: the moving version of this is called "picket fencing" due to the noise made when the signal is lost repeatedly.
Tunnels are an issue for satellite radio. They have to depend on buffer length to fill in the signal. I know someone who was high up the technical ladder at XM radio and complained that he lost the signal while driving through a tunnel under LAX, and they increased the buffer length as a result.
One comedian (can't recall who) had this gag: "I went for a drive with my friend. He's an AM radio announcer. He loses his voice every time he drives over a bridge." Referring, of course, to the old fashioned steel truss bridges, not the modern open concrete ones.