The question of what the radio cable is called often confuses novice radio amateurs and car enthusiasts who decide to install the equipment themselves. In everyday life, any wires are often confused, but in radio engineering, the quality of signal reception and the safety of the transmitter depend on the correct choice of conductor. The main element here is a coaxial cable, the design of which is specially designed for transmitting high-frequency signals with minimal losses.
Unlike conventional wiring used in a home electrical network, RF cable has a complex multi-layer structure. The center conductor is surrounded by a dielectric and braided shielding, which protects the signal from external interference. The wrong choice of cable type can lead to the fact that a powerful radio station will heat up, and a weak broadcast signal will simply be lost in the noise.
In this article we will examine in detail the technical characteristics, markings and applications of various types of radio frequency cables. You will learn to distinguish impedance (characteristic impedance) and understand why you can’t connect a television wire to a car radio without losing quality.
The main name and operating principle of coaxial cable
The correct technical name is coaxial cable. The term comes from the Latin "co" (together) and "axis" (axis), meaning "coaxial". This indicates the main design feature: the inner conductor and the outer screen have a common geometric axis. It is this geometry that allows radio frequency signals to be transmitted at high frequencies without allowing energy to radiate outward.
The central core, made of copper or copper-plated steel, transmits the signal itself. Around it there is a layer of dielectric (foamed polyethylene or Teflon), which fixes the core strictly in the center. A shielding braid is stretched over the dielectric, taking on the role of a second conductor and protection from interference.
The main task of such a design is to create a constant wave characteristic along the entire length of the transmission line. If the geometry is broken (the cable is pinched or has kinks), part of the signal is reflected back to the transmitter, causing heating and distortion. Therefore, it is so important for radio amateurs and car installers to observe the bending radius during installation.
Why can't I use regular twisted pair cable?
Twisted pair cable is designed to transmit digital signals and low-frequency data. At FM or CB radio frequencies (27 MHz), it works like an antenna, radiating a signal into space and catching interference, making transmission impossible.
Key Difference: 50 Ohm vs 75 Ohm
The most important parameter to pay attention to when choosing is characteristic impedance (impedance). It is measured in Ohms and has nothing to do with the usual electrical resistance of a conductor, which we check with a short circuit tester. In radio engineering, the de facto standard is two values: 50 Ohm and 75 Ohm.
Resistance cables 75 Ohm (for example, RG-6, RG-59, RK-75) are designed primarily for receiving signals. This is the standard for terrestrial and satellite television, as well as FM radios. They are optimized for transmitting the signal from the antenna to the receiver with minimal attenuation, but are not designed for high power transmission.
Resistance cables 50 ohm (for example, RG-58, RG-8X, RG-213, RK-50) are used for power transmission. These are the wires needed to connect car radios (CB, LPD, PMR), amateur transmitters and Wi-Fi antennas. Using a 75 ohm cable with a high power transmitter can cause the amplifier to overheat and fail due to high standing wave ratio (SWR).
Never use a TV cable (75 ohms) to connect a transmitting radio station (50 ohms), this will result in high SWR and possible equipment damage.
Explanation of popular markings: RG, RK and types of shells
On the market you can find many abbreviations that indicate the cable size and standard. The most common American classification RG (Radio Guide) followed by numbers. Russian markings are also found RK (RF Cable). Understanding these symbols will help you quickly find the product you need in the store.
Let's look at the main types used in cars and everyday life:
- 📡 RG-6 (RK-75) - the most common thin cable for television and FM antennas. Has one copper core and aluminum braid. Not suitable for power transmission.
- 🚗 RG-58 (RK-50-2) - a thin cable with a diameter of about 5 mm. Often used to connect car radios (CB band) and Wi-Fi routers. Convenient for installation in hard-to-reach places inside the car.
- 🏠 RG-8X (Mini-8) - an improved version of the RG-58 with lower losses, but a larger diameter. An excellent compromise for medium power mobile radios.
- 📡 RG-213 (RK-50-7) - thick, rigid cable with low losses. Used for fixed antennas and high-power transmitters where maximum efficiency is important.
Special attention should be paid to the shell material. For a vehicle, it is critical to use a cable with insulation made of PVC (polyvinyl chloride) or, ideally, PE (polyethylene), resistant to ultraviolet radiation, oil and temperature changes. Regular home insulation will crack in the cold and become sticky in the sun.
When laying cables in a vehicle, try to avoid places near the engine control unit (ECU) and high-voltage wires to minimize interference to the radio.
RF Cable Characteristics Comparison Chart
To make your choice easier, we have prepared a comparison table of the main parameters. Pay attention to the signal attenuation: the lower it is, the longer the route can be laid without an amplifier.
| Marking | Impedance (Ohm) | Diameter (mm) | Attenuation (100 MHz, dB/100m) | Main Application |
|---|---|---|---|---|
| RG-6 | 75 | 6.9 | 20 | TV, FM radio (reception) |
| RG-58 | 50 | 5.0 | 32 | Autoradio (CB), Wi-Fi |
| RG-8X | 50 | 6.1 | 25 | Mobile radios |
| RG-213 | 50 | 10.3 | 15 | Fixed antennas |
As you can see from the table, thicker cables (RG-213) have significantly lower attenuation, but are more difficult to install in confined vehicle spaces. Thin cables (RG-58) are more flexible, but at frequencies above 400 MHz (LPD/PMR), losses over a length of 5 meters can already be noticeable.
Nuances of choice for car radios
When installing a radio station in a car (be it a long-haul CB or a city Meganet), the choice of cable becomes a matter of safety and quality of communication. First of all, you need to evaluate the power of your device. For standard 4-10 watts, a high-quality RG-58 or RG-8X.
It is important to consider the length of the route. If you place a magnetic antenna on the roof and the radio is located under the dashboard, you will need about 4 meters of cable. In this case, losses will be minimal even on a thin wire. However, if the radio is installed in the trunk and the antenna is on the roof, the cable length can reach 6-7 meters, and here it is better to use RG-8X or even RG-213so as not to lose sensitivity.
Pay special attention to the connectors. In the automotive industry, the connector has become standard PL-259 (per cable) and SO-239 (on the body of the radio), often called simply "American". For higher frequencies (VHF/UHF) connectors are used N-type, which provide better matching and tightness.
⚠️ Attention: When soldering the PL-259 connector, do not overheat the cable. The dielectric insulation may melt, which will change the characteristic impedance at the soldering point and create a reflected signal. Use low temperature solder and flux for radio wiring.
☑️ Check before installing the antenna
Typical errors during installation and operation
Even the most expensive cable will not work correctly if you make mistakes when laying it. One of the most common problems is geometry violation. Coaxial cable it's impossible crumple, bend at an acute angle or stretch. At the bend point, the center conductor moves relative to the braid, which causes a mismatch.
The second error is poor contact in the connectors. Oxidation of contacts or poor-quality soldering introduces additional losses. In automotive environments where vibration and humidity are present, this causes communication to drop out intermittently. Always use heat shrink or special caps to protect joints.
The third mistake is laying the cable near sources of strong interference. The car wiring is full of impulse noise from the generator, ignition system and control units. By running the antenna cable along the main wiring harness, you are guaranteed to get noise in the speakers. Try to keep your distance or cross the standard wiring at a right angle.
⚠️ Attention: Never use regular twisting to extend the antenna cable. Twisting disrupts the wave impedance and turns the connection point into a source of interference and losses. Use only special connectors (feeders) or soldering while maintaining geometry.
Frequently asked questions (FAQ)
Can a TV cable be used for a car radio?
Technically, you can connect, but you shouldn’t do it. The television cable has a resistance of 75 ohms, and the walkie-talkie and antenna have a resistance of 50 ohms. This mismatch will cause some of the power to be reflected back into the radio (high SWR), which can damage the transmitter output stage and reduce communication range.
How to properly strip a coaxial cable for soldering?
You need to carefully remove the outer insulation without damaging the braid. Then the braid is turned back (“shaggy”) and the dielectric is removed from the central core. It is important not to damage the central core itself or make cuts on it, since this place will become a breaking point.
Does cable length affect reception quality?
Yes, it does. Any cable has attenuation, which increases with the length and frequency of the signal. For the FM range (60-100 MHz), losses over 5 meters of high-quality cable will be invisible. For the ranges of 400 MHz and higher (LPD, PMR), each meter of cable “eats” part of the useful signal.
What is SWR and why is it important when choosing a cable?
SWR (Standing Wave Ratio) is a measure of the matching between the antenna, cable and transmitter. The ideal SWR is 1. If the cable is selected incorrectly (for example, 75 Ohms instead of 50 Ohms) or the antenna is not tuned, the SWR increases. A high SWR (>2) means that a significant part of the power is not radiated, but heats the transmitter, which is dangerous for electronics.