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...

"KaitoWRX911" wrote in message
...
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...


Loop antennas are more efficient at lower frequencies, along with being more
directional, and less prone to noise pickup.

Many cheap shortwave radios used internal ferrite antennas (separate coils
on the same bar as the AM/MW antenna) for the main antenna tuned circuits on
the SW bands. This did allow some reception without using the whip.

For VHF/FM, the whip is more efficient because it can approach a 1/4
wavelength of the received signal.

"Brenda Ann" wrote in message
...

"KaitoWRX911" wrote in message
...
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...


Loop antennas are more efficient at lower frequencies, along with being
more directional, and less prone to noise pickup.

Many cheap shortwave radios used internal ferrite antennas (separate coils
on the same bar as the AM/MW antenna) for the main antenna tuned circuits
on the SW bands. This did allow some reception without using the whip.

For VHF/FM, the whip is more efficient because it can approach a 1/4
wavelength of the received signal.


The number #1 thing in radio is your ariel. Experiment with ant's!!!! Every
seasoned radio person will take a good ant with any reasonable RX over a
great RX with a mediocre ant. If your ariel isn't up to par, then it doesn't
matter how good your RX is.
--
Regards
B.H.
Hill Amplification
http://hillamplification.com

Brian's Radio Universe
http://webpages.charter.net/brianhill/500.htm

"KaitoWRX911" wrote in message
...
Why does FM and SW use whip antennas, while AM uses directional
internal ferrite-bar antennas?

HF transmissons may be reflected many times between transmitter and the
receiver. So the direction of the transmission is not so well defined.
Usually you don't have so good maxims and nulls with your ferrite antenna in
HF. With a piece of conductor you can have stronger signal.

Also the ferrite material is more expencive for higher frequencies than for
MF.
---timo

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)