Published on 10/13/2026 • Updated on 10/13/2026
Someone has 2 m of RG6 left over from a satellite install and a 50 ohm spectrum analyzer on the bench. Will the 75 ohm cable damage anything, or ruin the measurement? The answer is usually no for a short run at low frequency, but the numbers are worth knowing before you build a system around it.
Short answer: a 75 ohm cable in a 50 ohm system creates a 1.5:1 VSWR, a reflection coefficient of 0.2, and a mismatch loss of only 0.18 dB. About 4 percent of the power reflects. The bigger risks are bad connector fits and standing-wave effects on long runs.
This guide shows the math, what the mismatch does at different lengths and frequencies, and when you should never do it.
On This Page
The reflection coefficient at the junction is (Z2 - Z1) / (Z2 + Z1). From 50 ohm to 75 ohm that is 25 / 125 = 0.2.
Key idea: A single 50 to 75 ohm step costs about 0.18 dB. That is small. The problem is rarely the power lost. It is the reflections, the ripple across frequency, and the connectors.
| Situation | Effect | Verdict |
|---|---|---|
| Short run (under 0.1 wavelength), measurement | Negligible error | Usually fine |
| Long run with a 50 ohm source and load | Ripple of about 1.5 dB on a frequency sweep | Visible on a VNA or analyzer |
| Transmitter into 1.5:1 VSWR | Most radios fold back slightly above 2:1 | Safe for most radios |
| Quarter-wave length at your frequency | A 75 ohm quarter-wave section transforms a 50 ohm load to 112.5 ohm | Can detune amplifiers and filters |
| Precision calibration | Systematic error | Not acceptable |
The quarter-wave effect is real: for a 75 ohm section of length 1/4 wavelength, input impedance = 75^2 / 50 = 112.5 ohm. A half-wave section repeats the load, so 50 ohm. Between those, the input impedance swings, and the 1.5:1 VSWR shows up as frequency ripple.
Need the right impedance end to end?
SigmaRF builds 50 ohm assemblies to your length and connectors, each VNA-swept for VSWR and insertion loss before shipment.
Talk to an Engineer75 ohm BNC, SMA and N connectors exist, but their center pins are smaller. Forcing a thicker 50 ohm male pin into a 75 ohm female socket can spread the socket contact and leave a poor connection afterward. Check connector markings before you plug in.
| Connector | 50 ohm vs 75 ohm | Risk |
|---|---|---|
| BNC | 75 ohm uses a thinner center pin | 50 ohm male pin can damage a 75 ohm female socket |
| F connector | 75 ohm only | No 50 ohm version |
| N | Both exist | Check markings |
| SMA | 50 ohm standard | 75 ohm SMA is rare |
Usually acceptable
Do not do it when
Option 01
Use a 50 ohm cable
The cleanest fix. Replace the 75 ohm cable with RG58, RG316 or LMR types.
Option 02
Minimum-loss matching pad
A 50 to 75 ohm pad has about 5.7 dB of loss. It matches both ends, but costs signal.
Option 03
Quarter-wave transformer
A section with Z = sqrt(50 x 75) = 61.2 ohm matches the two over a narrow band.
Can you use 75 ohm cable in a 50 ohm system?
Yes for short runs and low power. Expect a 1.5:1 VSWR and about 0.18 dB of mismatch loss. Avoid it for calibration or phase-critical work.
What is the VSWR of 75 ohm into 50 ohm?
1.5:1, with a return loss of about 14 dB.
Will 75 ohm cable damage a 50 ohm transmitter?
Not normally. 1.5:1 is below the fold-back threshold of most radios, which is usually 2:1 or higher.
Can I use RG6 for a 50 ohm radio?
For a short run, yes. For a long run or higher frequency, use proper 50 ohm cable.
How much signal do I lose with a 75 ohm cable?
The mismatch loss is about 0.18 dB, plus the cable attenuation itself.
What is a 50 to 75 ohm adapter?
A matching pad or minimum-loss transformer. A resistive pad has about 5.7 dB loss. Simple adapters only change connectors, not impedance.
A 75 ohm cable in a 50 ohm system is rarely a disaster. It costs about 0.18 dB and a 1.5:1 VSWR. It becomes a real problem in measurement, precision, and narrowband systems, and when connectors do not mate cleanly.
When impedance matters, build it right. SigmaRF makes 50 ohm RF cable assemblies in India (Vadodara) and the USA (Cleveland area), with VNA sweep data and lead times as short as 2 days.
Get a correct 50 ohm assembly
Send us the connectors and length. We will quote it.
Standard AssembliesCustom AssembliesTalk to an Engineer