Cable loss calculator

Every metre of cable eats some of your transmitter power and weakens the received signal — and the higher the band, the worse it gets. Pick the band and length and I’ll compare the most popular coax cables (from the cheapest to low-loss), show the loss in decibels, how much power actually reaches the antenna and the ballpark cost of the run.

80 m – 70 cm cheap · mid-range · expensive loss in dB and % run cost

Calculate your cable How I calculate it

PL-259 (UHF/SO) plug crimped on a coaxial cable — antenna feeder

Your run

// choose band and length — the comparison updates automatically

Band

Cable length

20 m

Transmitter power

100 W

Transmitter power at the radio’s output. The calculator will show how much of it reaches the antenna after the cable.

Cable loss comparison

Run 20 m · band 2 m · 145 MHz · power 100 W

small loss (<1 dB) noticeable (1–3 dB) large (>3 dB)

How to read the result

Decibels aren’t linear. A 3 dB loss is half the power, 6 dB is only a quarter, 10 dB — one tenth. On receive it works the same way: the cable also attenuates the signal coming from the antenna to the radio. That’s why on 70 cm a good feedline can decide whether you hear a weak station or it drowns in the noise.

Prices are indicative (order of magnitude, Polish market, loose cable by the metre) — the actual cost depends on the shop, the length in one piece and fitting the plugs. “Run cost” is simply price per metre × your length, without connectors.

Under the bonnet

How I calculate the loss

No magic — it’s just standard feedline physics. The result is approximate, but it shows the differences between cables and bands well.

Attenuation model

Attenuation increases with frequency. For each cable I take the catalogue attenuation (dB/100 m) at two points and fit a curve A(f) = k₁·√f + k₂·f — the first term is conductor loss (skin effect), the second is dielectric loss. That’s where the value for your band comes from.
Run loss = attenuation per 100 m × length ÷ 100. I assume a matched line (SWR ≈ 1). With a high SWR the losses are higher — treat the result as a minimum.
Power at the antenna = transmitter power × 10^{(−loss_dB / 10)}. It’s the same relationship that gives the rule “3 dB = half the power”.
Receive. The cable attenuates the signal both ways — the same number of dB is subtracted from the signal received from the antenna.

Close-up of radio equipment — illustration for the technical section

✓

Practical conclusion: on HF (80–20 m) even a cheap cable hardly loses anything — there’s no point overpaying. On 2 m and 70 cm every metre counts twice: with longer runs a low-loss cable (Ecoflex / Aircell) can “give back” to the antenna as much power as an extra amplifier would — and it pulls the same on receive.

Related calculator

Work out the antenna range too

You’ve got the cable loss — now check how it translates into real simplex range, EIRP and the dimensions of the antenna to build.

Antenna calculator → 2 m / 70 cm guide