this was a qustion from my instractor in college

tomerbr schrieb:

this was a qustion from my instractor in college



1/4 wavelength is resonant to spread most of the power into the air (or
even into vacuum). Any multiple length of 1/4 wavelength works as well.

Explainig *why* 1/4 wavelength is resonant is just another thingy....

You can use allmost any mechanical length. By adding a coil or a
capacitor you can make it resonant electrically.
Lengths under one full wavelength will provide a somewhat near ground
radiation diagram. Longer antennas are directional towards the antenna
tip. This is not that good for vertical antennas other you want your
signal going to mars.


There are some special constructions like cophased antennas or multiple
dipoles in one unit. These antennas provide some to much gain over
simple verticlas as the radiation diagram flattens the diagram of
radiated power down to earth so that less radiated power goes out to
space. These antenna constructions can have the length of 1 to 5 (or
even more) full wavelengths.

Please excuse my bad and very simple english.
Season greetings from Berlin/ Germany.

thank you for the quick answer, however this is not true that any
resonant of the 1/4 wave length will give the same performance like the
normal 1/4 wave length antenna because for longer antennas the current
that runs through the antenna will start from the 1/4 wavelength of the
antenna and will go up as well as down with an opposite phase thus
decreasing the total current of the antenna.

If you can think of another reason way they build such antennas I will
be happy to know

Thanks again
Tomer

tomerbr schrieb:

thank you for the quick answer, however this is not true that any
resonant of the 1/4 wave length will give the same performance like the
normal 1/4 wave length antenna because for longer antennas the current
that runs through the antenna will start from the 1/4 wavelength of the
antenna and will go up as well as down with an opposite phase thus
decreasing the total current of the antenna.

If you can think of another reason way they build such antennas I will
be happy to know

Thanks again
Tomer


You must not compare pure radiated power to performance/ gain.
A 1/4 wave allways needs some ground or radials to perform reasonably
good by going 80% of the radiated power to mars as of high angle
radiation. This is somewhat useful in areas with high buildings with the
repeaters on top surrounding your place but not in rural areas.
A 1/2 wave vertical is much less affected by surrounding things (at last
your own body) within a 1/4 wave distance of the antenna and a 3/4
antenna has much lower radiation angle than the others. So real
performance is a very complex thing.
Those theoretical antennas in outer space vacuum are not really
comparable to the different conditions a cell-phone antenna has to work.

But... If you are so well educated why do you ask such 'simple' things
in a cb-group?
Even most radio-amateurs could not answer your question.
You may buy that ARRL Antenna Handbook for further information on
antennas of all kind.
Also you may use an antenna simulation program like EZnec to see how
*real* antennas perform.

regards

A 1/4 wave has a high angle of radiation.

If you look closely at a cellular antenna, it's two 1/4 waves
with a phasing coil between them. As explained above, this
concentrates the power to a lower angle.

857 MHz is about 3.03 inches for a quarterwave.
I've built antennas for our local 800MHZ public service band.


Volker Tonn wrote:
tomerbr schrieb:

thank you for the quick answer, however this is not true that any
resonant of the 1/4 wave length will give the same performance like the
normal 1/4 wave length antenna because for longer antennas the current
that runs through the antenna will start from the 1/4 wavelength of the
antenna and will go up as well as down with an opposite phase thus
decreasing the total current of the antenna.

If you can think of another reason way they build such antennas I will
be happy to know

Thanks again
Tomer


You must not compare pure radiated power to performance/ gain.
A 1/4 wave allways needs some ground or radials to perform reasonably
good by going 80% of the radiated power to mars as of high angle
radiation. This is somewhat useful in areas with high buildings with the
repeaters on top surrounding your place but not in rural areas.
A 1/2 wave vertical is much less affected by surrounding things (at last
your own body) within a 1/4 wave distance of the antenna and a 3/4
antenna has much lower radiation angle than the others. So real
performance is a very complex thing.
Those theoretical antennas in outer space vacuum are not really
comparable to the different conditions a cell-phone antenna has to work.

But... If you are so well educated why do you ask such 'simple' things
in a cb-group?
Even most radio-amateurs could not answer your question.
You may buy that ARRL Antenna Handbook for further information on
antennas of all kind.
Also you may use an antenna simulation program like EZnec to see how
*real* antennas perform.

regards

On 24 Dec 2005 01:38:11 -0800, "tomerbr"
wrote:

this was a qustion from my instractor in college

Why would a 1/4 wave length be ideal? If your instructor insists
that a 1/4 wave length is ideal then you must define ideal.

Hello, Tomerbr

Check out this URL:
http://groups.yahoo.com/group/HamRadioHelpGroup

We'll try and give you an honest answer.

Antennas can direct energy in an specific direction (and kill radiation in
other directions) to end up with a definite "gain" where you wish to
communicate with.

Check the group out or e-mail me with questions at


73 from Rochester, NY
Jim AA2QA


"tomerbr" wrote in message
oups.com...
this was a qustion from my instractor in college

tomerbr wrote:
this was a qustion from my instractor in college

GIGO they are not ideal merely one of the good number wrt to wavelength

On a sunny day (Tue, 27 Dec 2005 02:03:01 GMT) it happened "Jim Hampton"
wrote in :

Hello, Tomerbr

Check out this URL:
http://groups.yahoo.com/group/HamRadioHelpGroup

We'll try and give you an honest answer.

Antennas can direct energy in an specific direction (and kill radiation in
other directions) to end up with a definite "gain" where you wish to
communicate with.

Check the group out or e-mail me with questions at
I always thought 1/4 length was easier because you can make one easily from 1/1 length
by breaking in half exactly two times.
And then you have 4, so more economic too.

Hey Jim, you ever do Echolink anymore?
Can I find you on an Echolink linked repeater?

Give me a time and place.

I'm about ready to take over *BALT* and kick those foreigners off
with a bunch of English in their ears. It seems they only do it
to link the two conferences together. I'll write the owner of that
conference. I've known him for years.

Email me at my callsign email addy.
This one is over 800 messages behind.