Treebeard's Homepage : Stumpers

Treebeard's Stumper
30 November 2001

AM/FM Radio Blues

I generally prefer silence on my beautiful drive between school and home on San Marcos Pass, but sometimes the car radio is good company, usually 91.9 FM or 1250 AM. I've had good reception of both local stations since school started in September. But winter is approaching, and the days are shorter now, so I often drive home in the dark. I've noticed that I usually lose my AM station in the dark while my FM station is still clear. Why does the time of day make such a big difference in my radio reception? Other AM/FM radio stumpers will be appreciated as well as answers!

Here are a few more AM/FM radio stumpers. If I owned a cell phone or Ham rig, I'd probably have many more. Don't expect me to answer all these!

  • Why is the stretch of Highway 101 through Gaviota Pass such a black hole for radio?
  • Why do portable radios (usually) work inside metal cars and airplanes as well as solid buildings and tunnels?
  • Why does one car antenna work for both AM and FM? (Or does it?)
  • Why do I get better AM reception at night for distant stations, but loose my local stations?
  • My car antenna is adjustable, so is there a best antenna length for a particular station, say KCSB at 91.9 FM?
  • Why does it make a difference for FM reception where I stand in my classroom at school, but not at home? The signal at school disappears if I stand in the wrong place!
  • Why do portable cell phones and scanners and transceivers use short "rubber ducky" antennas, but my car needs a much longer whip antenna?

The photo (barely) shows the radio and TV antennas on top of 4000+ foot Broadcast Peak and Santa Ynez Peak, the western summits of the Santa Ynez Mountains.

Answer


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Copyright © 2001 by Marc Kummel / mkummel@rain.org