Frequency, MHz | 3.5 | 7 | 14 | 21 | 28 | 50 | 146 | 440 |
RG58A loss | 0.75 | 1.07 | 1.53 | 1.90 | 2.21 | 3.03 | 5.52 | 10.63 |
RG8X loss | 0.60 | 0.85 | 1.21 | 1.50 | 1.74 | 2.36 | 4.23 | 7.92 |
LMR240 loss | 0.46 | 0.64 | 0.91 | 1.12 | 1.29 | 1.73 | 2.98 | 5.23 |
RG213 loss | 0.27 | 0.39 | 0.57 | 0.71 | 0.83 | 1.16 | 2.20 | 4.50 |
RG8/9913 loss | 0.23 | 0.32 | 0.46 | 0.57 | 0.66 | 0.89 | 1.55 | 2.82 |
LMR400 loss | 0.23 | 0.32 | 0.45 | 0.56 | 0.64 | 0.87 | 1.50 | 2.66 |
From this table one can see that there is not much concern about cable loss below 50 MHz. This may be some incentive for upgrading of the license to be able to operate on the HF bands.
Another point of interest in designing antennas is that the velocity factor is different for various coax cables. RG58 foam coax has a velocity factor of 0.535. RG58A, RG58B, RG58C, RG213, RG214, and RG8 have a velocity factor of 0.66 . The velocity factor for RG8X is 0.79. 9914 cable has a velocity factor of 0.78, and 9913 cable has a velocity factor of 0.84 .
Velocity factor is used to determine the length of cable to be used for a specific wavelength, such as 1/2 wavelength. For antennas that are not resonant (SWR exists) it is adventageous to use a feed line that is a multiple of 1/2 wavelengths long.
The formula for determining the length of a half-wavelength of cable is:
L = VF x 492 / f
where L is the physical length of one half wavelength, VF is the velocity factor, and f is the frequency of interest.
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