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donut
Antenna-Theory.com Newbie
Joined: 22 Jun 2012
Posts: 4
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 Posted: Fri Jun 22, 2012 3:15 pm Post subject: question about electrical length of a center fed dipole |
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Im reading the ARRL 19th edition Antenna Book, chapter 2 of antenna fundamentals.
Under the section of "Impedance of a Center-Fed Dipole" it tells me that:
A center feed dipole can be any length electrically, as long as it is configured in a symmetrical fashion with two equal-length legs.
my question is what is the books meaning of "any electrical length". I suppose I am asking what defines "electrical length" |
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bigSteve
Antenna Wizard
Joined: 14 Mar 2009
Posts: 265
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| Posted: Fri Jun 22, 2012 6:30 pm Post subject: Electrical Length |
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| Electrical Length refers to the physical length divided by the wavelength of interest. This means we are measuring the length of the dipole in wavelengths. |
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donut
Antenna-Theory.com Newbie
Joined: 22 Jun 2012
Posts: 4
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| Posted: Sat Jun 23, 2012 2:36 am Post subject: Re: Electrical Length |
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| bigSteve wrote: | | Electrical Length refers to the physical length divided by the wavelength of interest. This means we are measuring the length of the dipole in wavelengths. |
So let me ask you this.
the formula for wavelength (in meters) is c/f. so the result of this answer is electrical length or physical length? |
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bigSteve
Antenna Wizard
Joined: 14 Mar 2009
Posts: 265
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| Posted: Sat Jun 23, 2012 1:24 pm Post subject: |
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Wavelength = c/f, that's right. This is an absolute physical length of the wave.
An example should clear this up:
Let's say we are talking about 600 MHz, so that the wavelength is 0.5 meters.
Suppose now we have something (a dipole antenna) that has a length of 3 meters.
Then:
Physical Length of the Dipole = 3 meters
Electrical Length of the Dipole = 6 wavelengths |
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donut
Antenna-Theory.com Newbie
Joined: 22 Jun 2012
Posts: 4
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| Posted: Sun Jun 24, 2012 2:55 am Post subject: |
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| bigSteve wrote: |
Let's say we are talking about 600 MHz, so that the wavelength is 0.5 meters.
Suppose now we have something (a dipole antenna) that has a length of 3 meters.
Then:
Physical Length of the Dipole = 3 meters
Electrical Length of the Dipole = 6 wavelengths |
600MHz wavelength = .5 meters
3 meter dipole = 100MHz
From your example I see that higher frequency has smaller wavelength.
I hate to keep beating this to death but I still have a question.
when you say that 600 MHz is .5 meters you are referring to a antenna that operates at 600MHz and the wavelength is .5 meters?
So when you are saying the electrical length of the dipole is 6 wavelengths you are basically saying that the dipole antenna is 6 wavelengths away from the 600MHz .5 meter antenna?
From your example I have gathered that higher frequency has smaller wavelength |
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Steve_Withnell
Antenna-Theory.com Newbie
Joined: 21 Apr 2013
Posts: 1
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| Posted: Sun Apr 21, 2013 1:59 pm Post subject: |
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| bigSteve wrote: | Wavelength = c/f, that's right. This is an absolute physical length of the wave.
An example should clear this up:
Let's say we are talking about 600 MHz, so that the wavelength is 0.5 meters.
Suppose now we have something (a dipole antenna) that has a length of 3 meters.
Then:
Physical Length of the Dipole = 3 meters
Electrical Length of the Dipole = 6 wavelengths |
HI Big Steve! Is there a simple model around that I can use to understand how the characteristics of short dipole (say 1/2 wave dipole at 150MHz) changes as a) the diameter of the elements changes and b) the conductivity of the element changes?
The characteristics would be bandwidth, radiation resistance, electrical length etc.
TIA
Steve |
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R. Fry
Antenna Theory Regular
Joined: 06 Jun 2011
Posts: 49
Location: Illinois USA
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| Posted: Mon Apr 22, 2013 12:52 pm Post subject: |
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Steve_W:
You could download the free version of EZNEC -- which can tell you the answers you're looking for.
http://www.eznec.com/demoinfo.htm |
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