Cable loss

How much the coax swallows on the way to the antenna, for common cable types and any frequency. Plus what an SWR at the antenna costs on top and how long λ/4 is in this cable.

Cable loss

From cable type and frequency, instead of hunting for the number in the datasheet. The values are rounded guide figures.

Cable

Frequency MHz

Length m

SWR at the antenna

How the page calculates

a(f) = k1 · √f + k2 · f (dB per 100 m, f in MHz)
k1 and k2 from the datasheet values at 100 and 1000 MHz
With SWR s: ρ = (s − 1) / (s + 1), α = 10^(a/10), total = 10 · log10((α² − ρ²) / (α · (1 − ρ²)))

The loss of a line grows with the square root of frequency through skin effect and linearly with it through dielectric losses. Two datasheet values are enough to find both parts, and in between the curve matches the datasheet to within a few tenths.

With a mismatch, the wave runs through the cable several times and is attenuated every time. That's why a long cable flatters the SWR reading: what the antenna reflects is attenuated again on the way back, and less of it reaches the transmitter.

Cable data the calculator uses

Cable	Z (Ω)	Velocity factor	dB/100 m at 100 MHz	dB/100 m at 1000 MHz
RG174/U	50	0,66	33	120
RG316	50	0,70	25	85
RG58 C/U	50	0,66	16	63
RG223	50	0,66	12,5	47
H155	50	0,79	8,4	30
Aircell 5	50	0,82	9,4	33
RG213/U	50	0,66	7	27
Aircell 7	50	0,83	6,1	21,5
Aircom Plus	50	0,85	4,5	15,4
H2000 Flex	50	0,83	4,3	14,4
Ecoflex 10	50	0,85	4,4	14,7
LMR-400	50	0,85	3,9	13
Ecoflex 15	50	0,86	3,1	10,2
RG59 (75 Ω)	75	0,66	11	45
RG11/U (75 Ω)	75	0,66	4,5	17
Ladder line 450 Ω	450	0,91	1	4

Rounded guide values from datasheets. Your cable's datasheet is what counts.

Related terms

Velocity factor: factor between free-space wavelength and physical length; RG58 has 0.66, one metre takes 5.05 ns in it, try it out under /leitung

SWR: standing wave ratio, a measure of the match between cable and antenna

Power budget SWR and return loss