Why does that happen. Driving down the road the sound quality changes and I see the HD light going on and off.
Yep, HD radio will do that. You are on the fringe coverage area for the digital FM signal, and as soon as you lose data lock, it drops into standard FM Stereo mode. You have to take into account where the transmitter antenna is, how much power they run, what their ERP footprint is, With that info, you can figure out where you can get good HD or not. Basically HD radio is not as good as they thought it would be! It needs way more power, so you can receive a usable signal. Simple.
HD Radio initially was allowed to transmit with 1% of the power of normal analog FM. That means a 100,000 watt FM station is only broadcasting HD radio at 1,000 watts. It's amazing it works anytime, anywhere. Clear line of sight can get you 45 miles or so but any obstruction or reflection at distance causes dropouts. The FCC was sold a bill of goods from a single manufacturer to use their system. I am sure some officials are living the high life now. Overseas countries use a different, better system. Recently changes in FCC regulations allow a station to go up to 4% HD power, but most stations bought the 1% equipment and are stuck with it. Additionally, if a station can prove an increase to 10% HD power would not cause interference, they can then petition the FCC to go to 10%. The single manufacturer makes the transmitting equipment, plus the corporate media owners don't care much especially when they can broadcast over the net to the world. Of course the net broadcasts are at low bandwidth and eat up your monthly cell contract. The sad thing is that HD radio sounds great when functioning, much much better than FM Stereo. The best thing to do right now is to get a longer antenna for the car (I did and it helps some) or stay closer to the town when listening to HD. By the way, HD2 and HD3 are mono, not stereo like HD1.
AM radio stations also broadcast an HD signal with quality sound. Same dropout problems though. JeffD
And let's not forget to mention the fix for this problem; On the radio screen, look for the HD tab and touch it to toggle HD on/off.. When the yellow indicator on the HD tab goes off the radio will use regular FM signals only.
I started seeing this same HD problem more over the past two weeks in the DC MD area. If I deselect HD then change channels, it comes back defaulted on again. Real annoying. My wife's 2004 Honda has a much better stock radio, pulls in all kinds of channels I can't get in my 2012 Prius.
I have an interesting experiment for you. Swap antenna between cars and test radio reception before and after swap.
