AM/FM radio performance

What you describe can often be caused by summer-time inversion layers. At least in Southern California, this is fact of life with FM signals. As heat layers stack up, FM signals can travel much further than normal. Distant signals can suddenly become strong, over taking local signals (or cause interference to adjacent channels).

A few weeks ago, I was in San Diego listening to a local station (stopped at a traffic light). All the sudden another FM station, over took the local one. In and out (for a couple of seconds), the completely over taking it. I tracked down the station that was "skipping" in... it was from Coalinga, CA (north of Fresno)! This is FM (not AM).

Now another problem I've noticed with the Prius (and probably all modern cars) is with the FM radio. HD radio basically sucks. Because it will drop out and revert back to a lower bit rate. If you have a mountain (or hill) between you and the transmitter site, you can notice the high end go away first. Then it drops back to analog and the radio will blend back into mono (as a means of dealing with FM multi-path interference/distortion).

I have a broadcasting background. The Prius is my first new car with HD radio. Those are some of my observations (so far) after 2 months of ownership.

If you want to geek out more on summer-time inversion layers, read on:

Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (7,620 m). Such signals are thus directly affected by weather conditions extending over some hundreds of miles. During very settled, warm anticyclonic weather (i.e., high pressure), usually weak signals from distant transmitters improve in strength. Another symptom during such conditions may be interference to the local transmitter resulting in co-channel interference, usually horizontal lines or an extra floating picture with analog broadcasts and break-up with digital broadcasts.

 

HD radio leaves a lot to be desired.

 

What makes you suspect it is an antenna issue?

If dropped and replaced signals are on the same frequency, that is seems mostly likely to be a local signal strength issue in the air, before even reaching the antenna. If both stations are heard simultaneously, garbled together, then it would be a combination of signal strength and radio performance issues (good radios can reject the weaker signal, but none can handle matched signals). If the dropped and replaced signals are on different but close frequencies, then it is more likely a radio performance issue.

 

Then that would be a "diversity antenna" design... which is far superior.

Funny, I've studied that pattern on the rear window, trying to determine what part was the antenna and what is the window defroster. I've not found definitive information on that.

In another thread, I was trying to get info on the radio antenna and if the shark fin on the roof is just the satellite or GPS antenna?