If you’ve ever stood in an RF system design meeting, whether you’re a engineer prototyping a 5G small cell, a hobbyist building a satellite ground station, or a tech lead outfitting a broadcast studio, one question comes up more often than almost any other: what impedance should I use for my RF cables? For many years, I’ve answered this question dozens of times a week as an RF cable supplier, and I’ve watched even seasoned engineers second-guess themselves: is 50 ohms still the standard, or did I mix that up with 75? And why does it even matter, anyway? RF Cable
Let’s start with the basics, because if you skip the “why” behind impedance, you’ll end up ordering the wrong cable for your project, and that’s where signal loss, power waste, and even equipment damage creep in. RF cables are transmission lines, meaning they carry high-frequency alternating current (AC) from a source (like a transmitter) to a load (like an antenna). Impedance, in this context, is the total opposition that the cable’s conductors, dielectric material, and surrounding environment put up to that AC current at a specific frequency. It’s not a static number—its value shifts a tiny bit based on temperature, frequency, and the length of the cable, but for practical use, we talk about the nominal impedance: the standard value that cable manufacturers design for and that systems are built around.
Now, here’s the most common question I get from first-time buyers: what’s the typical impedance for most RF cables? For nearly 80% of the RF applications our team supplies, the answer is 50 ohms. That didn’t happen by accident. Back in the 1940s, during the early days of radar research at Bell Labs, engineers were testing two competing standards: 50 ohms and 75 ohms. They landed on 50 ohms for a perfect middle ground: it balances two critical performance factors that matter for high-power, high-frequency signals. First, it minimizes resistive loss (loss from the cable’s conductors) for signals carrying high power, which was non-negotiable for military radar back then. Second, it also minimizes the reactance (loss from the electric and magnetic fields around the cable) for signals at radio frequencies. No other impedance at the time hit that sweet spot so well: 75 ohms, the other top contender, has lower resistive loss but much higher reactance, making it less ideal for the high-power use cases that were the backbone of early RF development.
That legacy stuck around, and by the 1960s, 50 ohms became the universal standard for almost all commercial and industrial RF applications. Let’s break down where you’ll find 50 ohm cables today: cell phone towers, Wi-Fi routers, GPS devices, two-way radios, test and measurement equipment, satellite communication systems, and even most amateur radio setups. If you’re working on anything that needs to transmit power efficiently over a medium or high frequency (from 1 MHz up to 100 GHz, which covers nearly every RF use case), 50 ohms is the go-to. Our team stocks dozens of 50 ohm cable variants, from thin, flexible RG-316 for compact IoT devices to heavy-duty LMR-400 for outdoor 5G small cell runs, because that’s what most of our customers need.
But wait—75 ohm cables are also extremely common, and that’s where a lot of new buyers mix things up. What are they used for? 75 ohms is the standard for video and home entertainment RF applications: coaxial cables for cable TV, satellite TV, and indoor broadcast video signals. Why? For low-power, high-frequency signals like video, reactance isn’t as big of a concern as it is for power transmission. 75 ohms is even better at minimizing reactance for those specific, low-power use cases, and it’s been standardized for broadcast and home audio-visual equipment for decades. We supply a range of 75 ohm cables too, but they only make up about 15% of our total sales—mostly for professional broadcast installations and satellite TV setups, not for general RF systems.
You might run into less common impedances too, though they’re rare for most everyday applications. 93 ohm cables, for example, were used in some early military and aerospace radar systems, and they’re still used today for certain specialized applications like air traffic control. 120 ohm cables show up in some industrial Ethernet and low-frequency RF control systems, and even 300 ohm twin-lead cable—remember the old rabbit ear antennas on TVs? That’s a legacy impedance, now mostly obsolete for modern RF. But again, these are the exception, not the rule. For 99% of the RF cables sold today, the typical impedance is either 50 ohms or 75 ohms, with 50 ohms making up the vast majority.
Now, let’s talk about why this matters more than just a random number. If you mix up 50 and 75 ohm cables, the results can be costly. When a transmission line (that’s your RF cable) doesn’t match the impedance of the source and load, you get a phenomenon called standing waves. Those standing waves bounce back and forth along the cable, wasting power, creating signal distortion, and even causing damage to sensitive transmitters if the mismatch is severe enough. I’ve seen it happen: a small business owner ordered 75 ohm cable for a new two-way radio system, and within a month, their base station’s transmitter burned out because of the impedance mismatch. They lost thousands in equipment and downtime, just because they didn’t confirm the impedance standard for their use case.
That’s why, as a supplier, we make sure to spell out impedance clearly on every cable product page, and our sales team always asks customers to confirm their application before they order. For example, if you tell us you’re setting up a new Wi-Fi network or a 5G antenna run, we’ll recommend 50 ohm cable, not 75. If you’re running a cable for your home TV or a professional broadcast studio, we’ll point you toward 75 ohm. We also test every batch of cables we produce to ensure their nominal impedance falls within industry standards—no cutting corners here, because even a 5 ohm deviation in a 50 ohm cable can cause noticeable signal loss at high frequencies.
There’s another common misconception I hear all the time: that all high-frequency RF cables use 50 ohms. That’s true for most cases, but there are exceptions even within high-frequency. For example, some satellite communication systems use slightly custom impedances for very specific signal optimization, and some mmWave 5G components are moving toward new standardizations, but 50 ohms still remains the baseline. The only time you’ll consistently run into a different impedance is when you’re working with video or entertainment RF signals, which is still dominated by 75 ohms.
Let’s also touch on how impedance is specified, because it’s not just a number on a label. When we say a cable has a nominal impedance of 50 ohms, that refers to the characteristic impedance, which is the impedance that the cable presents when it’s terminated with its matching load. It’s calculated based on the cable’s inner conductor diameter, the dielectric material between the inner and outer conductors, and the outer conductor’s diameter. For example, a cable with a solid polyethylene dielectric and a copper inner conductor will have a different impedance than one with a foam dielectric, because the dielectric’s capacitance per unit length changes, which directly impacts impedance. That’s why every cable type has a fixed impedance—changing any of those physical dimensions changes the impedance, so manufacturers have to stick to tight tolerances to keep performance consistent.
As RF technology evolves, we’re seeing small shifts in standards, but the core impedances haven’t changed in decades. 50 ohms is still the standard for industrial, commercial, and most consumer RF equipment that transmits signals, and 75 ohms is still the standard for video and broadcast. That means if you’re ordering RF cables for a new project, you can almost always rely on one of those two numbers. But the key is to confirm which one your equipment requires—check your transmitter, antenna, or device manual, because that will almost always specify the exact impedance needed.
I’ve been in this industry long enough to know that even experienced engineers sometimes mix up 50 and 75 ohms, and even small mistakes can lead to big problems. That’s why our team prioritizes transparency with every customer: we don’t just send a box of cables—we make sure you have the right impedance for your job, and we’re here to answer any questions you have about performance, installation, or matching. If you’re planning an RF setup, whether it’s a small home network, a commercial broadcast installation, or a large-scale 5G deployment, don’t hesitate to reach out to our team to discuss your requirements. We can help you choose the right cable, confirm the impedance standard, and make sure your system is set up to minimize signal loss and perform reliably.
25G SFP28 References
- Rogers, J. A. (2000). Radio Frequency Transmission Line Principles and Applications. McGraw-Hill.
- Pozar, D. M. (2012). Microwave Engineering (4th ed.). John Wiley & Sons.
- ITU-R Recommendation BT.1699-2 (2019). Impedance Standards for Video and RF Transmission Systems. International Telecommunication Union.
- Bell Labs Historical Document 45-12 (1945). Standardization of Coaxial Cable Impedance for Radar Applications. AT&T Archives.
- EIA-364-29A (2021). Electrical Test Methods for RF Cables and Connectors: Impedance Measurement. Electronic Industries Alliance.
Shenzhen Circle Interconnect Electronics Co., Ltd.
Address: Building 47, the second industrial zone,Tianliao community, Yutang street, Guangming District,Shenzhen City, Guangdong Province, China
E-mail: sales@szcircleinterconnect.com
WebSite: https://www.szcircleinterconnect.com/
