How to Test a Coax Cable? [Check Signal Loss / Strength]

Are you bogged down with frequent signal outages? Are the signal drops becoming too difficult to endure? Although coaxial cables are durable, they are vulnerable to damage with prolonged exposure to heat, wear & tear, or moisture. With the damages not being apparent, it gets trickier to narrow down to the root cause. And that’s when you’re required to test the coax cable.

It saves you a lot of time if you know how to test a coax cable. If you are eager about the details involved in testing coax cables for signal loss, this article is just for you. You’ll learn about different methods of troubleshooting coax cable and the list of the ‌equipment required to test coax cable as you go further into the guide.

Requirements & Overview

One reason behind the signal loss & performance could be your coaxial cable, the sole reason being exposed to the external environment. If you have to narrow down the issue, you’ll require certain tools before you begin.

What do you need?

You can test if a coax cable is live with two different tools.

  • The coax cable tester – A tool easy to understand even for beginners.
  • Electrical Multimeter – Don’t let those colored wires scare you.

In case you don’t have any of the tools handy, you can still figure out and tell if the coax cable is bad. Curious to know how?

  • Use your cable modem and test every cable outlet manually.

Different Tests

A coaxial cable comprises a copper wire at its core, a dielectric insulator, a metal mesh layer, and an outer plastic sheath. To ensure all the components are intact, you’ll have to conduct three different tests using a multimeter.

The center conductor continuity test: This test checks the continuity of the copper conductor wire, which confirms that the copper wire is in good condition to carry the signals.

The shield continuity test: Shields are essential to reduce interference. Testing the continuity in the shield at different ends ensures the shield layer is intact. It prevents outside interference and signal leaks.

The shield to center test: The test is performed to determine continuity between the copper conductor wire and the shield. Continuity, if detected here, signifies a short in the cable, and it’s due to be replaced.

Frequency range test (with coax cable tester): The dedicated coax cable testers can scan specific frequency ranges to determine an active connection. It avoids situations of false-positive signals in your coaxial outlets.

Things to Remember

When checking coaxial cable signal quality, ensure that both ends of the cable are removed from any active connection. The cable shouldn’t be attached to coaxial outlets, i.e., cable splitters, tv outlets, or modems.

In the next section, you will understand how to test cable signals and find out if the cable is the primary reason for the malfunction and poor performance.

How to Test Coax Cable Signal with Multimeter?

Test Coax Cable Signal with Multimeter

Testing coax with a multimeter can be easy and convenient. With three simple tests, you’ll be able to figure out if the coax cable is bad and find solutions to avoid its repeat.

Step 1: Connect the red and black testing prong to the respective slots. Switch on the multimeter and set the black knob towards the Ohm sign.

Step 2: Take one end of the coaxial cable that is required to be checked for live signals and touch the red probe to the center copper wire. Similarly, take the black probe and touch the copper wire at the other end of the coaxial cable.

If you hear a long beep and notice the Ohm indicator reading move, the coaxial cable’s center copper wire has continuity and is intact. If the multimeter reading doesn’t move or moves very little, that shows a loss of signal in copper wire.

Step 3: Repeat the process but instead of the center wire, now connect the shields at either end of the coax cable with the red and black probes.

A long, loud beep shows continuity in the shield, which determines the shield is also intact. Anything otherwise shows a faulty shield and requires attention.

If the coaxial cable fails in any of these tests, it is at fault and warrants a replacement.

Why do they happen?

The main reason behind the failure of the copper wire or insulator, or shield is physical wear and tear. Using connectors at ‌junctions would reduce the flexing or twisting of the outer plastic shield, ‌reducing the impact on the layers beneath.

Another way to minimize physical damage is to invest in a high-grade coaxial cable. The multiple layering and shields offer more protection against physical damage and interference.

How to Test Coax Cable without Multimeter?

There are two ways to test a coax cable without a multimeter. There is an easier way that uses a more sophisticated coax signal tester. If you don’t have the signal tester, you have no option but to go for a more tedious way; using your cable modem. In this section, we’ll see the steps involved in both methods.

Testing Coaxial Cable with the Coax Signal Tester

Using the coax signal tester is an easy solution for apartments to test coax outlets and signal output from coaxial cables.

Step 1: Move the knob to the “on” side.

Step 2: Plug it into the coaxial outlet or any signal output and press the highlighted button.

If the light turns green, there is a valid coaxial signal. The coaxial tester looks for a particular frequency for a valid internet signal. If the light turns red, it denotes an inactive outlet or malfunctioning coaxial cable.

Using a Modem to Test Cable Outlet

You can use a cable modem with an active internet service to test cable outlets or signals from the coax cables. The only hardship is moving the modem around.

Step 1: Ensure you have an active working internet connection at your place. Switch off the modem and use the cable to be tested to connect to the active coaxial outlet to your modem, as shown in the image below.

Step 2: Switch on the modem and wait for the lights to turn on. If the internet light turns green and the modem connects to the internet, the coaxial cable transmits signals. If the internet LEDs don’t light up, you’ll know the coaxial cables are at fault.

In case you need to test other cable outlets, you’ll have to move the modem and ensure you are using a tested coaxial cable to check if the cable outlet is active.

Frequently Asked Questions

How to tell if coax cable is bad? Can it go bad?

Yes, a coax cable can go bad. Any exposure to excessive heat, water, or physical wear tear can affect the cable. You can use an electrical multimeter to check if your coax cable is working or needs a replacement. Conduct resistance, capacitance, and inductance checks will determine the reason behind the defect.

Can the length of the cable affect the signal transmission?

Yes, the length of the cable affects signal quality. The longer the cable, the greater the distance the signal has to traverse, making it vulnerable to signal loss. Limiting the cable length to less than 15-20 ft will keep the loss to a minimum. We expect anything more than 50ft to cause over 20% loss to the signal strength.

What can cause the loss of signal strength?

There are two major causes of signal loss. One is the resistance of the conducting material (copper wire). Increased exposure to the conductor’s resistance will increase the chance of loss of signal strength. The type of insulator and its durability in coax cables are determinant factors of signal quality.

How do you measure antenna signal strength?

Standards use a combination of two metrics to measure the antenna’s signal strength, i.e., Noise margin (NM) in dB and Power ratio in dBm. The noise margin gives you the ratio of static signals (noise) in your signal, and the power ratio gives the actual strength of the signal.

How to improve the signal quality?

There are two ways to limit the loss in signal strength and improve the quality. Keep your coaxial cable away from electrical lines and use a quad-shielded cable to minimize interference. Keep the length of your coax wiring to a minimum.


Depending on the device you have at your disposal, you’ll be able to test whether the coax outlet is live or if the cable is a reason behind the loss of signal quality and performance. The article focuses on different methods of testing coax cables for signal loss.

It also offers clarity on how to check coax cable. While the methods and tools can be helpful to find out what is at fault, it is essential to recognize that these methods don’t measure the signal strength, which requires a different digital meter.

Suggested Read: Routers with Coax Input