How to Test a Coaxial Cable with a Multimeter

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Here is how to test a coaxial cable with a multimeter: disconnect both ends, check the center pin against the shield for a short, then check the center conductor and the shield end to end, or put a terminator on the far end and read the whole run in one step. A multimeter finds opens and shorts and little else. Lectromec found that a cable with a partly cut shield read the same as a new one, so a pass does not prove signal quality.

Quick answer

Safety first: work on mains circuits can kill, a meter’s CAT rating must suit the circuit, and panel or service work belongs to a licensed electrician. Power down and unplug equipment, and disconnect the coax from it, before any reading.
If you can reach both ends, read center to center and shield to shield for near zero, and center to shield for an open circuit.
For a long run, a 75 ohm terminator on the far end lets one reading at the near end test the run. Viasat’s job aid calls a reading of 75 ohms a pass.
A pass says nothing about loss, impedance or a partly cut shield.

Electrical safety first

OSHA’s booklet on controlling electrical hazards says an electric shock can range from a slight tingling sensation to immediate cardiac arrest, and that only qualified electricians trained in lockout procedures should maintain electrical equipment. A coax test belongs on the safe side of that line, because the cable is disconnected and nothing in the test touches a mains circuit.

Viasat’s field job aid, written for satellite internet installers, shows the order of work. Before it reaches for a meter, the job aid says to disconnect the AC power cord from the power source to power down the modem, and then to disconnect the coax and Ethernet cables from the modem and from the TRIA at the other end of the run. Fluke explains that category ratings are defined by the IEC 61010 standard and that a meter and its leads must be rated for the category and voltage of the job. No meter is named in this guide, so no CAT rating is stated here. If your meter’s listing does not state a CAT rating, do not treat it as safe for household mains. Outlets, panels and service wiring are out of scope and belong to a licensed electrician.

What a coaxial cable is made of

Lectromec, an electrical wiring test laboratory, describes the basic construction as a single core conductor in the middle of an insulating layer called the dielectric, a conductive layer called the shield, and an outer jacket. That layout tells you what to expect from a meter. The center conductor and the shield are two separate metal paths, so each should conduct along its own length, and the dielectric between them should not conduct at all.

Manufacturer datasheets give the numbers for a specific cable. The Belden 1694A datasheet describes a 75 ohm, RG-6 type cable with an 18 AWG solid bare copper conductor and a foil plus tinned copper braid shield. It lists a nominal conductor resistance of 6.4 ohms per 1000 feet and a nominal outer shield resistance of 3.8 ohms per 1000 feet. A second datasheet, for a 50 ohm RG-8 type cable with a 10 AWG conductor, lists 0.9 ohms per 1000 feet for the conductor and 1.8 ohms per 1000 feet for the shield. These are two examples, not a universal rule, and the datasheet for your own cable is the right reference.

What a multimeter can and cannot find

Lectromec’s first article carries a blunt summary: multimeters are not the tool to use for coaxial cables. In its test, a 12 inch cable had 5 mm of jacket and shield removed around 270 degrees at its center. The conductor and shield resistances still read about 0.0 ohms after the test leads were subtracted, the same as a new cable. Lectromec explains that enough shield remained to carry the multimeter’s test voltage.

Fault	Can a multimeter find it?	What the sources say
Open center conductor or shield	Yes	Viasat’s coax test exists to discover a short or an open on a run.
Short between center and shield	Yes	Same job aid.
Partly cut shield	No	Lectromec’s damaged cable read the same as a new one.
Changed capacitance or impedance from limited damage	No	Lectromec reports 33.6 pF for the damaged cable and 34.4 pF for the new one.
Where along the run a break sits	No	Lectromec’s second article says a time domain reflectometer can help find broken or shorted wires.

The second Lectromec article adds that attenuation and standing wave ratio tests also showed little difference between the damaged and new cables. For a cable with a signal problem and a clean multimeter result, the pages we opened point toward a time domain reflectometer or similar radio frequency gear, not more meter work. Our roundup of pocket toner coaxial cable testers covers one kind of dedicated tool.

Before you start

Check the meter. Viasat’s job aid does this first. Set the ohms range to its highest position, hold the probes apart, and confirm the display reads one on its meter, then touch the probes together and confirm it reads zero. Fluke says an open pair of leads on a typical meter shows OL, so the symbol varies by meter.
Check the leads. Fluke says good leads read about 0.5 ohms or less when the tips touch, and that relative mode subtracts the lead resistance, typically 0.2 to 0.5 ohms.
Disconnect everything. Power down the equipment and take the cable off it, as the Viasat job aid does.
Inspect the cable. The same job aid lists what to look for when no meter is available: visible cable damage, poor or loose fittings, and sharp bends of more than 90 degrees.

Reading the numbers: what a good cable should show

Because the conductors are copper, their resistance is tiny over short runs. The formula is simple: resistance equals the datasheet figure in ohms per 1000 feet, times the length in feet, divided by 1000. The table applies it to the two datasheet examples above. The figures in the table are our own arithmetic from the datasheet values.

Length	Example 75 ohm cable: center	Example 75 ohm cable: shield	Example 50 ohm cable: center	Example 50 ohm cable: shield
6 ft	0.04 ohm	0.02 ohm	0.01 ohm	0.01 ohm
25 ft	0.16 ohm	0.10 ohm	0.02 ohm	0.05 ohm
50 ft	0.32 ohm	0.19 ohm	0.05 ohm	0.09 ohm
100 ft	0.64 ohm	0.38 ohm	0.09 ohm	0.18 ohm
150 ft	0.96 ohm	0.57 ohm	0.14 ohm	0.27 ohm

Two lessons follow. First, for a short cable the expected values sit below the typical 0.2 to 0.5 ohm that Fluke gives for lead resistance, which is why Lectromec subtracted the leads and why relative mode matters. Second, a reading of exactly zero on a run that is many feet long would be a surprise, but the pages we opened give no pass or fail threshold for coax resistance, so treat the table as an expectation and not a limit. Readings this small are what dedicated low-resistance instruments are built for, as in our roundup of milliohm meters.

Method 1: a cable you can reach at both ends

A patch cord or a short jumper falls in this group. Lectromec used this approach on its 12 inch samples, measuring conductor and shield resistance with a standard meter and subtracting the leads. The steps below follow that idea. The short check in step 3 is our own reasoning from the cable’s construction, because the pages we opened do not describe it for a loose cable.

Center to center. Put one probe on the center pin at one end and the other on the center pin at the other end. Expect near zero after the leads are accounted for.
Shield to shield. Put the probes on the outer metal of each connector. Expect near zero.
Center to shield at one end. The dielectric separates them, so an intact cable should show an open circuit. A reading near zero suggests a short.
Wiggle the cable at each connector while you watch the display. Fluke’s automotive guide advises wiggling wires during testing to expose intermittent issues.

Keep your fingers off the metal parts of the probes. Fluke explains that the human body acts as a parallel resistance path and lowers a reading. For a general walk-through of the beeper setting, see our guide on how to use a continuity tester.

Method 2: a long run with a terminator at the far end

An installed run has its two ends in different rooms, so one set of probes cannot reach both. Viasat’s job aid handles that with a terminator, and it is the most completely sourced procedure in this guide.

Prove the meter, as described above.
Power down the equipment and disconnect the coax from it at both ends.
Place a barrel connector and a 75 ohm terminator on one end of the cable. The job aid specifies a 3.0 GHz barrel.
At the other end, touch the red probe to the outside shield of the connector and the black probe to the center conductor.
Read the display. The job aid says that a reading of 75 ohms means the cable has neither a short nor an open and has passed.

The same job aid lists two failing results, a reading that fluctuates between zero and one, which it calls a short, and a reading of zero, which it calls an open. We do not build advice on those two labels. The job aid’s own meter check says that probes held apart read one, which sits oddly beside calling a zero reading an open cable, and the page does not explain the difference. The 75 ohm pass result is the part we can use.

Because the terminator sits in series with the cable, a good run should read slightly above 75 ohms. On the 75 ohm example cable, a 100 foot run adds about 1.02 ohms (0.64 for the center and 0.38 for the shield), so the display would sit near 76 ohms. A 150 foot run adds about 1.53 ohms. That is our arithmetic, and the job aid states no tolerance for the terminator, so a small difference from 75 is not alarming by itself.

When the run fails

Viasat’s job aid suggests working in sections: if a problem is found in a section, replace only that section before testing the cable again and moving to the next. Checking connectors and fittings first is consistent with it, since the job aid names loose fittings as a defect. Repeating the terminator test on a shorter section is our own extension of the idea. Where a break is somewhere inside a long run, Lectromec’s second article says a time domain reflectometer can find broken or shorted conductors.

How we chose

We opened ten pages on 2026-10-22. Viasat’s job aid supplies the most complete meter procedure for coax. Lectromec supplies the construction description and the evidence about what a multimeter misses. The two Belden datasheets supply the resistance figures behind the table. Fluke supplies the meter facts about leads and open readings, and OSHA supplies the safety background.

We kept a step only when one of those pages describes it, and we labeled the two places where we added reasoning of our own. Where the Viasat job aid and ordinary meter behavior seemed to disagree, we said so. We did not rank cables or meters.

Mistakes to avoid

Testing a cable that is still attached to equipment. The job aid powers down and disconnects first.
Treating a pass as a clean bill of health. Lectromec’s damaged cable passed a resistance check.
Ignoring lead resistance. On a short cable the leads can add more than the cable.
Touching the probe tips. Fluke says the body lowers the reading.
Forgetting the terminator on a long run. Without it, one end cannot tell you about the far end.
Assuming every coax matches the example numbers. The datasheet for your cable is the source.

What we could not verify

What the sources do not say

The pages we opened give no pass or fail resistance limit for a coax conductor or shield, no tolerance for a 75 ohm terminator, and no instruction for an installed run with a different termination. They do not describe a far-end jumper method, so this guide does not give one. The Viasat job aid is written for one provider’s installations, and Lectromec’s tests used 12 inch samples of an aerospace cable, not household cable. The resistance table covers two datasheet examples only.

No meter is named here, so this guide states no CAT rating, counts or fuse rating. None of the pages says whether a given coax carries DC voltage in service, so the guide’s safe practice is to power down and disconnect first, as Viasat does.

Frequently asked questions

Can a multimeter tell me whether a coax cable is good?

It can find opens and shorts. It cannot find the damage in Lectromec’s sample, where a partly cut shield read the same as a new cable, and it says nothing about attenuation or impedance.

What should center to shield read on a coax cable?

With both ends open, an intact cable should read open, because the dielectric separates the conductors. That expectation is our reasoning from how the cable is built. With a 75 ohm terminator on the far end, Viasat’s pass value is 75 ohms.

How much resistance should a coax cable have?

It depends on the cable. One RG-6 type datasheet lists 6.4 ohms per 1000 feet for the conductor and 3.8 for the shield, and a 10 AWG RG-8 type lists 0.9 and 1.8. Look up the datasheet for your cable.

Do I need a terminator?

You need one for the single-reading method on a long run, as in Viasat’s procedure. If you can reach both ends, the center-to-center and shield-to-shield readings do not need one.

Is it safe to test coax while it is connected to a modem or TV?

The job aid we opened powers equipment down and disconnects the cable first. OSHA adds that qualified electricians should maintain electrical equipment, so leave anything beyond a disconnected cable alone.

What tool finds signal loss in coax?

Not a multimeter. Lectromec describes attenuation tests, standing wave ratio tests and time domain reflectometry as the techniques it used on the damaged cable.

Bottom line

Disconnect the cable, prove the meter, read the run with a terminator or end to end, and treat a pass as proof of continuity only.

Sources

https://eguide.field.viasat.com/repair-tests/coax-cable-test/ (opened 2026-10-22)
https://lectromec.com/blog/coaxial-cable-damage/ (opened 2026-10-22)
https://lectromec.com/blog/coaxial-cable-damage-part2/ (opened 2026-10-22)
https://catalog.belden.com/techdata/EN/1694A_techdata.pdf (opened 2026-10-22)
https://catalog.belden.com/techdata/EN/9913_techdata.pdf (opened 2026-10-22)
https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-resistance (opened 2026-10-22)
https://www.fluke.com/en-us/learn/blog/digital-multimeters/testing-your-test-leads (opened 2026-10-22)
https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-for-continuity (opened 2026-10-22)
https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-perform-automotive-continuity-checks-with-a-multimeter (opened 2026-10-22)
https://www.osha.gov/sites/default/files/publications/OSHA3075.pdf (opened 2026-10-22)