Calculating antenna length

[pathalogical]

How do you calculate the antenna length based on the frequency you want to listen ? I know that hight freqs use shorter length and lower freqs use longer lengths. What is the math calculation to figure out the length you want for a particular freq and is the calculation the same for any other frequency ?

 

[JRichard]

This thread should answer your questions.

Antenna Lengths per band

 

[Arcticpeak]

Lenght (ft) = 492/frequency (MHz)
Lenght (m) = 142,5/frequency (MHz)

 

[Al42]

Lenght (ft) = 492/frequency (MHz)
Lenght (m) = 142,5/frequency (MHz)

These give you 1/2 wavelength. Use half these numbers for a 1/4 wave vertical (or ground plane).

 

[RevGary]

One handy calculator listed in the formulas area in an ARRL Antenna Handbook gives this one for the VERTICAL element length in INCHES of a 1/4 ground plane:

5905 divided by the Frequency in MHZ, divided by two, MINUS 5% wave velocity factor.

For 1/4 wave resonant length @ 155.000 that would be -

5905/155.000 = 38.097/2 = 19.04 minus 5% 0f 19.04 (.95 inch) = 18.09 inches.

The ground radial length is calculated the same way BUT the wave velocity factor is + 20% which would be ~ 22.85 inches. The droop angle of the ground radials within this formula is 10 degrees below perpendicular to the vertical element or a vertical to radial angle of 100 degrees.

 

[pathalogical]

Thanks all for the very useful info and calculations.