Is there something different about AM today compared with 20 years ago. Back then, all AM stations would fade under bridges (whereas FM stations would not-was this a function of shorter wavelength?). Today, however, some commercial AM stations (1010, 770, and 660 in NYC for examples) do not fade beneath overpasses (in fact, they come in great even driving downtown under the covered part of the FDR). However other stations (eg. 820 our public radio affiliate) still fade significantly. Do the no-fade stations just have a stronger signal? Or is there some other explanation for this phenomenon?
i think its due to am(amplified) not to sure see other thread What does am/fm stand for?
There haven’t been any significant changes in AM (mediumwave) station transmitters or powers in the last 20 years, so for underpasses I don’t have an explanation, unless you have a better receiver in your current car than you used to have. (WINS-1010, WABC-770 and WCBS-880 all transmit with 50 kilowatts of power, while WNYC-820 is only 10 kilowatts).
For the FDR tunnel, the explanation is that technically you aren’t listening directly to the stations, but instead to low-power retransmissions runnning through the tunnel, and operated by the tunnel authorities. Normally these rebroadcast the signals of selected stations, but in case of a problem in the tunnel, all the transmissions within the tunnel would be switched to emergency messages.
My wager for the overpasses is your '90s radio with digital tuning is better at picking up weak signals than a '70s radio with The Knob.
Radio transmission is affected by the seasonal changes. In Winter, there is a harder time getting some stations in that would be clear during the summer. The same thing happens with television reception via antenna.
It has to be your receiver. My AM not only fades but gets static by telephone wires, underpasses, etc. In fact, I can get NOAA weather on my car radio, at the lowest frequency on the AM dial. I also get traffic reports, if there are any delays, at the same frequency. (I get them both at the same time if there are any traffic reports.) However, the power is so low, the slightest interference causes static.
It’s been many years since I even attempted to listen to AM. Every time I have the radio tuned to AM frequencies, I mostly get a loud electronic hum that nearly drowns out the signal. Makes me wonder how anyone can stand to listen to AM any more.
I like AM. I use it near my laptop, in fact, but I have to lay my cheapo walkman ripoff radio on the floor under the PC and the monitor (both of which cause interference). I get a pretty good signal from a local station even in the proximity of electrical and electromechanical devices (engines, TVs, computers, florescent bulbs, etc.) as long as I’m not right next to them.
Anyway, AM is cheaper than FM and it carries much farther, especially on clear nights when the ionosphere is favorable. I can regularly get Radio Havana (actually from Miami, IIRC) and some European stations (the BBC, among others) at night on my shortwave radio, and shortwave uses AM methods to encode audio on the carrier. Pretty good for someone using a consumer-grade model in north-central Montana.
Now that springtime is upon us, our station engineer is faced with one of his most difficult jobs: explaining how “leaf attenuation” degrades our signal. No, I didn’t believe him either. And I still don’t understand it.