Radio reception question
AM (Amplitude Modulation) antenna had adjustable length to trim to wave amplitude . Low (560) end of band has a different height wave compared to high end (1650). FM, (Frequency Modulation) or length of wave does not require adjustable antenna length for opptamal reception.
Most older car Am radios have a small trim adjustment screw located somewhere on case of radio that sometimes needs to be turned to tune or adjust radios electronics to antennas impedance when a change in antenna or radio is made. I dont recall just which frequency one tunes to in order to perform this trim procedure, but Im sure its on line somewhere. Once antenna is properly trimmed, reception will generally improve.
More on trimming here: http://www.electronicspoint.com/am-fm-car-radio-antenna-trimmer-t75872.html
One other reason AM reception is inconsistent throughout the broadcast day is federal regulation of station signal out-put has to be lowered after sun down excepting a few grandfathered 50,000 watt clear channel stations such as WBZ, WOR, WABC, etc. which are generally the pioneer station first to broadcast in North America.
Here in Maine one can pick up most of these clear channel stations once the ionosphere settles down after sunset within a 2000 mile radius, best reception being just before sun rise.
More on this here: http://en.wikipedia.org/wiki/Clear-channel_station
Now, that brings back memories. I was in college in Daytona Beach, FL in the early 1970s. I used to listen to WABC radio on a cheap bedside clock-radio at night.
