antenna length

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performance87
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antenna length

Post by performance87 » Tue Oct 29, 2002 9:24 pm

what is the formula for figuring antenna length

bobsRAC
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Re: antenna length

Post by bobsRAC » Tue Oct 29, 2002 10:30 pm

c = 3x10^8 m/s (300,000,000 m/s)<p>1/4 wave whip antenna<p>length = c/(4*f) meters<p>example:<p>2.4 GHz - (3x10^8)/(4*(2.4x10^9)) = 3.125 cm<p>900 MHz - (3x10^8)/(4*(9x10^8)) = 8.333 cm<p>27 MHz - (3x10^8)/(4*(2.7x10^7)) = 2.778 m

performance87
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Re: antenna length

Post by performance87 » Tue Oct 29, 2002 10:53 pm

I don't understand the math but maybe you can help.Can you give me the lengths on quarter wave
320 mgz
460 mgz
800 mgz
125 mgz
75 mgz

bodgy
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Re: antenna length

Post by bodgy » Wed Oct 30, 2002 3:06 am

bobsRAC has just presented the standard formula in a slightly different way - try this<p>Radio Waves travel at 300,000,000 metres/second
If you have the frequency (f) and you want to know wavelength in metres(m) then you just divide 300,000,000 by the frequency eg:
wavelength = 300,000,000/320,000,000 (320MHz)
wavelength = 0.9375 metres or if you prefer 93.75cm :confused: hope not!
a 1/4 wavelength is 93.75/4 =23.44cm.<p>Conversely take your 0.9375m and divide your speed of light the 300,000,000 by 0.9375 and hey presto you have converted wavelength back into frequency.<p>Bobs example only looks strange because he used the short hand way of expressing numbers as 10 to the power of; and he included the divide by 4 in one go.<p>[ October 30, 2002: Message edited by: bodgy ]</p>
On a clear disk you can seek forever.

Duane
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Re: antenna length

Post by Duane » Sun Nov 03, 2002 7:18 pm

Hello, Most antennas are dipoles and the formula
is as follows, I = 468 / frequency in MHZ
example 468 divided by 75 Megahertz is 6.24 feet
is the length overall. With a dipole, each side
would be 3.12 feet. hope this helps.

Bernius1
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Re: antenna length

Post by Bernius1 » Mon Nov 04, 2002 6:46 am

My brother had a 16 ga. bell-wire dipole in the
eaves of the house. On L.I., he rcvd. Maryland
stations in clear stereo(5-gang Realistic tuner).
But I'd be more interested in the equations for..
Reactance of a wire antenna based on its parallel distance from the gnd.plane, and..
How to determine coil dimentions on an extended
whip. ( Like Nextel's 5db gain trunk mount).
Whip out those calculus books !!!!!
Can't we end all posts with a comical quip?

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