In article ,
KaitoWRX911 wrote:
Why does FM and SW use whip antennas, while AM uses directional
internal ferrite-bar antennas? Couldn't the internal antenna be used
for SW and FM, or vise-versa? Thanks... excuse my ignorance...

Why not use a ferrite loopstick for SW and FM?

1. The ferrite core has a frequency response that depends on it's
chemical and material structure. The formulas used for AM antennas
quits working well enough to make it worthwhile up around 3-10 MHz.

2. Loopsticks are tuned antennas, so getting them to track the
tuning of the rest of the radio at higher frequencies can be difficult.

Why not use a whip for AM?

1. They do. Examples: the E1 and most car radios use whip antennas.
But they're high impedance, from being so small a fraction of the
wavelength at that frequency. So they'll pick up noisy electrical
fields from power lines and stuff with static charges more than
a loopstick.

2. They need a ground or counterpoise (which for a battery powered radio
sitting on a table will be the stray capacitance of the circuitry with
the rest of the universe). I find I can better reception of FM on my
FR-200 (with a whip) using headphones, because the headphone cord (and
my body) becomes the other half of the antenna.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)