Transmission line calculation formula
where:
f = frequency in MHz     
VF = velocity factor

Electrical wavelength 983.6/f x VF = length in feet
Electrical wavelength 491.5/f x VF = length in feet
Electrical wavelength 245.8/f x VF = length in feet

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Antenna lengths (wire)

Length of 1/2 wave antenna = 492 x K/f
where:
f = frequency in MHZ   
K= ~.095 for 1/2 wavelength / diameter

3/4 wavelength Length(ft) = 736 x 0.95/f   699.2/f
5/8 wavelength Length(ft) = 615 x 0.95/f   584.3/f
1/2 wavelength Length(ft) = 492 x 0.95/f   467.4/f
1/4 wavelength Length(ft) = 246 x 0.95/f   233.7/f
1/8 wavelength Length(ft) = 123 x 0.95/f   116.9/f

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Coaxial Baluns

Single Band (Very Effective)
Freq, MHz   RG-213, RG-8           RG-58
3.5          22 ft,   8 turns       20 ft, 6-8 turns
7            22 ft,  10 turns       15 ft,   6 turns
10           12 ft,  10 turns       10 ft,   7 turns
14           10 ft,   4 turns        8 ft,   8 turns
21            8 ft, 6-8 turns        6 ft,   8 turns
28            6 ft, 6-8 turns        4 ft, 6-8 turns

Multiple Band
Freq, MHz RG-8, 58, 59, 8X, 213
3.5-30    10 ft,    7 turns
3.5-10    18 ft, 9-10 turns
14-30      8 ft,  6-7 turns

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Radiation resistance of short mobile antennas

Rr = 395 × (h/l)2
where:
h = radiator height in meters
l = wavelength in meters = 300/Freq in MHz

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System Q is controlled by the Q of the coil. 
The bandwidth between 2:1 SWR points of the system
BW = 0.36 × F/Q.

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-- 40m --
7.00
7.05
7.10
7.15
7.20
7.25
7.30

-- 17m --
18.068
18.108
18.168

-- 30m --
10.100
10.125
10.150