"David Combs" wrote in message
...
In article ,
Michael A. Terrell wrote:
micky wrote:
On Fri, 09 Nov 2012 22:18:39 -0500, "Michael A. Terrell"
wrote:

...
I don't think so. And if that were the case, then a
radio transmitter broadcasting at 600 KHz would require an antenna
that was a third of a mile long.

No, it doesn't. AM BC band broadcast antennas are not a full
wavelength, and the aren't resonant at the transmit frequency.

Please say more about that. Thanks!

AM radios use a ferrite cored coil antenna that picks up the magnetic
component of the RF wave, so they don't have to be sized to the
wavelength like FM and TV antennas.
http://www.radio-electronics.com/inf...od_antenna.php

I built an audio-band VLF radio receiver as a kid with a large folding
air-core coil antenna made from a scrapped TV yoke.
http://en.wikipedia.org/wiki/Dawn_ch...lectromagnetic)
I had to hike it far from the roads to reduce 60Hz hum from power
lines.

They all
use use L/C networks to make the tower work at the allocated
frequency.

What, some kind of impedance matching?

The antenna should look like a pure resistance that absorbs (and
radiates) the incoming signal completely. SWR or Standing Wave Ratio
is an indication of how far out it is.
http://en.wikipedia.org/wiki/Standing_wave_ratio

It's difficult to write a simple, intuitive but accurate explanation
of this stuff. Thus I practice. The principles of AC circuits do not
relate to everyday experience. I was surprised by how well the
mathematics of the "imaginary" square root of -1 describe inductive
and capacitive circuits.

Some ATU are as large as the AM transmitter when the tower is
difficult
to configure.

ATU -- what's that?
Thanks!
David
PS: And if you feel like writing a bunch, give us all a tutorial!