Published on 10/13/2026
An antenna stops working after a storm. The installer has a cheap multimeter and a spare 5 m RG58 jumper. He needs to know in five minutes whether the cable or the radio is dead.
A multimeter will answer exactly one question: are the conductors connected the way they should be? It cannot tell you VSWR, insertion loss or impedance. But it finds opens, shorts and broken connectors, which are the faults behind most dead antenna lines, and it costs nothing to try.
This guide gives you a safe five-step test, a table of readings and what they mean, the faults a meter cannot see, and a clear point where you should move to a VNA or cable analyzer. For care and cleaning see our connector care article, and for failure prevention see our strain relief article.
On This Page
| A multimeter can find | A multimeter cannot find |
|---|---|
| Open center conductor or shield | High VSWR or poor return loss |
| Short between center and shield | Excess insertion loss |
| Broken or loose connector contact | Moisture that has not yet shorted the line |
| Wrong wiring or wrong pin | Kinks that still conduct |
| Gross damage from a crush or cut | Impedance mismatch and bad crimps that still touch |
Step 01
Set the meter
Use the lowest resistance range or continuity mode. Touch the probes together and note the reading, usually 0.1 to 0.5 ohm of lead resistance.
Step 02
Check center-to-center
Probe the center pin at each end. For a cable up to about 10 m you should read below roughly 2 ohm. An open reads OL or infinity.
Step 03
Check shield-to-shield
Probe the connector bodies (outer conductor) at each end. Expect a similarly low value. An open here means a broken shield or a loose ferrule.
Step 04
Check center-to-shield
Probe center pin to connector body at one end. A good cable reads open. Any low resistance means a short, usually from a crimp, a stray braid strand or water.
Step 05
Flex and re-test
Wiggle the cable and each connector while watching the reading. A flickering value points to a broken conductor or poor crimp at that spot.
| Test | Reading | Meaning | Action |
|---|---|---|---|
| Center to center | Under 2 ohm (short cable) | Conductor intact | Pass |
| Center to center | OL / infinite | Open center conductor or connector | Replace or re-terminate |
| Shield to shield | Under 1 ohm | Shield intact | Pass |
| Shield to shield | OL / infinite | Broken shield or loose coupling | Replace |
| Center to shield | OL / infinite | No short | Pass |
| Center to shield | Under 10 ohm | Short circuit | Replace or re-terminate |
| Center to shield | Hundreds of ohms to kilohms | Moisture or contamination | Dry and clean, then retest |
| Any | Flickers on flexing | Intermittent break | Replace |
A common mistake is to measure 50 ohm across the cable. That figure is characteristic impedance, a high frequency property of the geometry. An ohmmeter sees DC resistance only, so a good cable reads open between center and shield, not 50 ohm.
If you cannot reach both ends, put a short on the far end: a shorted BNC, SMA or N terminator or a paperclip jumper across the connector. At the near end, center to shield should now read a low resistance (under a few ohms). A reading of open means the cable is broken between you and the short. Remember to remove the short afterwards.
For long runs or buried cable, a multimeter cannot say where the fault is. A cable analyzer or VNA with distance-to-fault gives the location, often within a few centimeters. See our guide to building a reliable VNA bench.
Move to a VNA or cable analyzer when
Distance-to-faultReturn lossInsertion lossVSWR sweepTime-domain trace
How do I test a coax cable with a multimeter?
Set the meter to continuity or low ohms. Check center-to-center and shield-to-shield for low resistance, then center-to-shield for open. Flex the cable while watching the readings.
What resistance should a good coax cable read?
Center-to-center and shield-to-shield should read under a few ohms on a short run. Center-to-shield should read open.
Can a multimeter measure 50 ohm impedance of coax?
No. Impedance is a high frequency property. A multimeter measures DC resistance only.
How can I tell if coax cable is bad?
A short or open on the multimeter, a visible crush or cut, corrosion, or intermittent readings while flexing all indicate a bad cable. A VNA is needed for subtle faults.
Why does my coax pass continuity but not work?
A multimeter does not see excess loss, high VSWR, impedance mismatch or moisture. Test with a VNA or cable analyzer.
Should coax read a short between center and shield?
No. A reading near zero ohms between center and shield means a short and the cable is faulty. Some devices with DC blocking or terminations read differently, so disconnect first.
How do I find a fault in a coax cable?
Use a cable analyzer or VNA with distance-to-fault or time-domain mode, which locates the reflection point.
Can I test a coax cable that is already installed?
Yes, by shorting the far end and measuring center-to-shield at the near end, or by testing each end with the cable disconnected.
A multimeter is the right first tool for opens, shorts and bad connectors, and the wrong tool for anything involving RF performance. Test in five steps, flex the cable, and escalate to a VNA when the cable passes but the signal still fails.
SigmaRF assemblies are VNA-swept for VSWR and insertion loss before shipment, from 100 MHz to 40 GHz, so a new cable arrives with measured data. If your multimeter test shows a bad cable, send us the connector types and length and we can build a replacement from our India (Vadodara) or USA (Cleveland area) facility, with lead times as short as 2 days.
Cable failed the test?
Send us the connector types and length for a tested replacement.
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