Car antenna cable: how to choose, connect and avoid interference

Why cable quality affects radio and GPS reception more than the antenna itself

Have you ever noticed that the radio in your car starts to “whistle” or “rip” the sound at speed, although the antenna is apparently intact? Or does the GPS navigator lose its signal under bridges, although it used to work reliably? In 80% of cases the problem is not in the antenna, but in cable, which connects it to the head unit. A cheap or damaged cable can “eat up” up to 50% of the signal before it even gets into the radio.

Car antenna cables are more than just “wires.” They must withstand vibrations, temperature changes from -40°C to +80°C, as well as electromagnetic interference from on-board electronics. For example, RG58 is a popular choice for FM radio, but is poorly suited for GPS due to high loss at frequencies above 1 GHz. A RG174, on the contrary, is ideal for satellite dishes, but too thin for mechanical strength in off-road conditions. How not to make a mistake with your choice and not overpay for unnecessary characteristics - we’ll figure it out below.

In this article we will not talk about “magic” signal boosters (they often only worsen the situation). Let's focus instead on physics: how cable length, material and shielding affect reception quality, and why even an expensive antenna will be useless with the wrong cable.

Types of cables for car antennas: comparison of RG58, RG59, RG174 and others

All antenna cables are divided into coaxial - this means that there is a central core inside them, surrounded by insulation, braided shielding and an outer sheath. But even among coaxial cables, there are critical differences that determine their applicability in a car.

Here are the main types you'll find in stores:

• 📡 RG58 - “gold standard” for FM/AM radio. Characteristic impedance 50 ohm, diameter ~5 mm. It holds the signal well at frequencies up to 1 GHz, but loses up to 30% of its power over a length of 10 meters.
• 📶 RG59 - thicker (75 Ohm), more often used for video signals (such as rear view cameras). Rarely used in radio systems due to impedance mismatch with most antennas.
• 🛰️ RG174 - thin (50 ohm, diameter ~2.5 mm) and flexible. Ideal for GPS/GSM antennas, but requires careful installation - the braid breaks easily.
• 🚗 RG316 — military-grade version with Teflon insulation. Expensive, but withstands extreme temperatures and vibrations. Used in professional systems (for example, walkie-talkies in SUVs).
• 💰 LMR-400 - premium class for audiophiles. Signal loss is 2 times lower than that of RG58, but the price starts from 300 rubles/meter.

Which one to choose? It all depends on the task:

Antenna type	Recommended cable	Max. length without amplifier	Features
FM/AM radio	RG58 or RG59	5–7 meters	RG59 is better shielded, but requires an adapter for 50 ohm antennas
GPS/GLONASS	RG174 or RG316	3–4 meters	RG316 is preferable for regions with frosts below -30°C
DAB+ (digital radio)	LMR-400 or RG6	up to 10 meters	DAB+ is susceptible to interference - requires double shielded cable
CB radio (27 MHz)	RG58 or RG8X	up to 20 meters	RG8X is thicker and runs cooler at high transmit power

⚠️ Attention: Never use "television" cable RG6 for FM antenna without adapter! Its characteristic impedance 75 Ohm does not match the impedance of most auto antennas (50 ohm), which leads to signal reflection and losses of up to 40%.

How cable length kills the signal: loss calculations and practical tips

Every meter of cable is signal attenuation. For example, at RG58 losses amount to about 0.2 dB/meter at 100 MHz (FM radio) and 0.6 dB/meter at 1.5 GHz (GPS). It seems that this is not enough, but:

• 📉 With a length of 5 meters you lose up to 30% signal strength at GPS frequencies (it's like listening to the radio with your ear covered).
• 🚫 If the cable is damaged (for example, pinched by a door), losses increase by 3-5 times.
• ⚡ At high frequencies (DAB+, 4G) even 1 meter of low-quality cable can “eat up” more signal than 5 meters LMR-400.

How to calculate the allowable length? Use the formula:

Max. length (m) = (Antenna signal level (dB) – Receiver sensitivity (dB)) / Loss per meter (dB/m)

Example: you have a gain antenna +3 dB, the radio is sensitive to -10 dBm, and the cable RG174 loses 0.5 dB/m on GPS frequency. Then:

Max. length = (3 – (-10)) / 0.5 = 26 meters

But this theoretical maximum! In practice:

• For FM radio, do not exceed 5–7 meters (even with RG58).
• For GPS - maximum 3–4 meters (better RG174 or RG316).
• For CB radios (walkie-talkies) you can up to 10–15 meters, but you need a low loss cable (RG8X).

Shielding: why a cheap cable “catches” interference from the engine

A car is an “electromagnetic hell.” The starter, ignition system, alternator, even LED headlights create interference that can drown out a weak GPS or radio signal. Cheap cables (for example, "no-name" from China) often have single layer braid with less than 60% coverage - this is not enough to protect against interference.

Compare shielding levels:

Shielding type	Coverage, %	Anti-interference	Cable example
Braid	60–80%	Weak (suitable for FM only)	RG58 cheap brands
Foil + braid	90–95%	Medium (good for GPS)	RG174, RG316
Double braid + foil	98%+	Excellent (for DAB+, walkie-talkies)	LMR-400, Times Microwave

How to check shielding in practice?

1. Connect the antenna and turn on the radio on a weak station (where there is usually interference).
2. Start the engine and listen to the sound change. If there are clicks or hissing — shielding is weak.
3. Try touching the cable with your hand. If reception deteriorates, the braid is damaged or too thin.

⚠️ Attention: If you are laying the cable near high voltage wires (such as spark plugs), use cable with ferrite rings (for example, RG58 with ferrite filter). They suppress high-frequency interference from the ignition system.

The braid does not “crumble” when bent|The central core is made of copper (not copper-plated aluminum)|The sheath does not crack in the cold|There is a certificate of conformity (for example, ISO 6722 for cars)|Resistance is indicated on the marking (50 or 75 Ohm)-->

How to lay a cable correctly: 7 mistakes that spoil the signal

Even the most expensive cable is useless if it is installed incorrectly. Here are typical mistakes and their consequences:

• 🔌 Bends at 90° → The central core may break and the braid may be torn. The bending radius must be at least 5× cable diameter.
• 🔥 Laying next to heating elements (exhaust pipe, radiator) → The shell melts, the insulation loses its properties.
• 🧲 The cable is located next to the speakers or power cords → Noise from the magnetic field degrades reception.
• 🚪 The wire is pinched by the door or trunk lid → Microcracks in the braid → interference.
• 🌧️ Moisture got under the insulation → Corrosion of the central core, short circuit.
• 🔗 Twisting instead of soldering → Contact oxidation, signal loss up to 50%.
• 📡 The cable is not secured → Vibrations rub against the body, erasing the braid.

How to lay the cable correctly:

1. Use corrugated tubes (for example, DuraFlex) for protection against mechanical damage.
2. Secure the cable plastic ties in increments of 30–40 cm (not metal!).
3. To pass through the body, use rubber bushings (for example, from 3M), so as not to fray the shell.
4. If the cable passes through the engine compartment, wrap it in heat shrink tube with an adhesive layer.

What to do if the cable is already damaged?

If the braid is torn, the shielding can be temporarily restored using aluminum tape (for example, 3M 425), wrapping it around the damaged area. But this is not a long-term solution - it is better to replace the cable. If the central core is broken, it can be soldered, but the soldering area must be insulated heat shrink and check with a multimeter for a break.

Connectors for car antennas: what they are and how to crimp them yourself

The cable is useless without the correct connector. There are three main types used in cars:

• 📻 FME - standard for most FM antennas (for example, on Pioneer, Sony).
• 🛰️ SMA — for GPS antennas (often found on Garmin, Navitel).
• 🚗 Motorola — an outdated connector, but still found on old radios.

How to crimp the connector yourself:

1. Remove the outer sheath of the cable 10–15 mmwithout damaging the braid.
2. Divide the braid into two parts and twist it into a rope.
3. Remove the insulation from the central core on 5–7 mm.
4. Place the connector on the cable so that the central core goes into its core and the braid goes into the metal casing.
5. Crimp the connector crimper (for example, Knipex 97 53 05). Do not use pliers - they will compress the cable unevenly!

Typical crimping problems:

Problem	Reason	How to fix
No signal	The central core does not touch the connector core	Re-crimp, making sure the contact is made
Traffic interference	Poor contact of the braid with the connector body	Add solder or use screw terminal connector
The connector is loose	Insufficient crimp	Crimp again or use heat shrink to secure

Frequent problems and their solutions: from noise to complete lack of signal

Situation: the radio is noisy, the GPS is losing satellites, or the signal disappears when the headlights are turned on. Here is the diagnostic algorithm:

1. Check the cable for visible damage (kinks, cracks, traces of oxidation).
2. Connect the antenna directly to the radio (without cable). If the signal appears, the problem is in the cable.
3. Swap antennas (for example, connect a GPS antenna to the FM input). If the problem “moves”, the cable is to blame.
4. Check supply voltage (for active antennas). It must be 12 V (not 5 V from USB!).

Typical symptoms and their causes:

• 🔊 Radio noise at speed → Poor shielding of the cable or it is laid next to high-voltage wires.
• 📵 GPS does not pick up satellites in the city → The cable is too long or damaged. Try it RG174 no more than 2 meters long.
• 🔋 The signal disappears when the headlights/heater are turned on → Insufficient power supply to the active antenna. Check the fuse.
• 🎵 The radio works, but the sound is broken → Oxidation of contacts in the connector. Clean them WD-40 Contact Cleaner.

⚠️ Attention: If you are using signal booster, make sure it is installed in front of the cable, and not in the salon. An amplifier after 5 meters of cable is useless - it will amplify noise along with the signal.

FAQ: Answers to frequently asked questions about cables for car antennas

Can I use RG6 TV cable for car antenna?

Technically possible, but only with impedance adapter (with 75 Ohm on 50 ohm). Without an adapter, you will lose up to 30% of the signal due to impedance mismatch. For GPS or DAB+ RG6 absolutely not suitable - too high losses at high frequencies.

How to check a cable for a break without a multimeter?

Connect the antenna to the radio and bend the cable slightly in different places. If reception improves/deteriorates, there is a break or short circuit. You can also listen to the radio on a weak station and tap the cable with a plastic handle - a crackling sound or changes in sound will indicate the problem area.

Do I need to solder the connectors or is crimping enough?

The crimp is sufficient for most cases, but soldering gives more reliable contact, especially for active antennas. If you drive off-road or in regions with high humidity, it is better to solder the central core and braid, and then insulate with heat shrink.

Why did GPS work worse after replacing the cable?

Probable reasons:

1. The new cable is too long (maximum for GPS is 3 meters).
2. Resistance cable used 75 Ohm instead of 50 ohm.
3. The connector is crimped incorrectly - check the contact of the central core.
4. The cable is laid close to sources of interference (for example, the engine control unit).

Which cable should I choose for a CB radio (walkie-talkie) in my car?

For CB radio (27 MHz) will do RG58 or RG8X. Main requirements:

• Wave resistance - 50 ohm.
• Thickness of at least 5 mm (thin cables heat up during transmission).
• Shielding of at least 80% (double braiding is preferred).

For stationary radios in the garage you can use LMR-400 - it has lower losses over long distances.