RG58 vs RG400: Which 50 Ohm Coax Cable Should You Use?

RG58 vs RG400 is a choice between two 50-ohm coax cables that look interchangeable — same 4.95 mm (0.195 in) jacket diameter, same BNC, SMA, and TNC connector families — but that are built to different specification sheets and fail in different ways once heat, frequency, and inspection limits are involved.

Short answer

• RG58 is enough for short, room-temperature runs below 1 GHz. Its military detail sheet does not specify performance above 1 GHz at all.
• RG400 is the choice when the cable runs hot (rated to +200 °C), works above 1 GHz, needs a second braid, or has to pass documented RF acceptance testing.
• Neither one is a low-loss cable. At 400 MHz the MIL-DTL-17 limits are 17.0 dB/100 ft for RG58 and 10.5 dB/100 ft for RG400. For a long feeder, move to a larger foam-dielectric cable instead of upgrading within 4.95 mm.

This comparison uses three things you can check on paper before ordering: the published specification limits, the loss over your real cable length, and what the finished assembly has to survive. Aircraft or vehicle work adds one more step — the assembly still has to meet the project’s own approvals, and no cable family provides that by itself.

RG58 and RG400 are both 50 ohm coax choices, but their construction and reliability are different.

Quick Comparison

These are Global RF Tech’s own GLRG58 and GLRG400 specifications. Both share the same 4.95 mm jacket diameter, while GLRG400 uses PTFE/FEP materials and has a wider stated temperature range plus a VSWR specification extending to 6 GHz. Those documented differences make it a same-diameter candidate for more demanding builds; final attenuation, shielding, and compliance still depend on the exact part and finished assembly. RG names describe a cable family, so always confirm the exact part datasheet before you buy.

What the Military Detail Sheets Actually Say

Most RG58 vs RG400 comparisons mix numbers from different vendors, so you end up comparing one company’s typical value against another company’s maximum value. There is a cleaner way. Both cables have a public detail sheet under the same US military specification, MIL-DTL-17, and both sheets state maximum attenuation at the same frequencies.

Sources: MIL-DTL-17/28C and MIL-DTL-17/128C, published by the US Defense Logistics Agency. These are specification limits, not typical values. Commercial cable is usually better than the limit, and a cable sold as “RG58” is not obliged to meet it at all.

Three lines in that table are worth pausing on.

• The voltage rating is identical. Both sheets cap continuous working voltage at 1,400 V rms, even though catalogue pages often advertise 1,900 V for RG400. If you are justifying the upgrade on power handling alone, the specification does not back you up.
• RG58 has no specification above 1 GHz. MIL-DTL-17 stops giving RG58 an attenuation limit at 1 GHz, while RG400 is specified to 12.4 GHz. For Wi-Fi, GNSS, or 2.4 GHz test work, that missing specification matters more than the loss difference.
• The RG58 detail sheet is inactive for new design. M17/28-RG058 has been marked inactive for new design since 13 August 1993, with new designs pointed to MIL-C-17/183. RG58 is still made in huge volume, but no one is required to build it to a current military standard, which is exactly why quality varies so much between suppliers.

What RG58 Is Good For

RG58 is a common 50-ohm coax used in radio, wireless, antenna, and instrumentation applications. Global RF Tech’s GLRG58 is a 50-ohm cable with a tinned-copper inner conductor, solid PE insulation, tinned-copper braid, and a PVC jacket at 4.95 mm overall diameter, rated -40 to +85 C with VSWR under 1.20 from DC to 3 GHz.

That makes RG58 a practical fit for short RF cable assemblies where cost and availability matter. It can be used for short antenna leads, radio jumpers, test bench cables, wireless equipment wiring, and general 50-ohm connections.

The important word is short. If the run gets longer, the frequency rises, or the installation is exposed to heat and vibration, RG58 should not be chosen just because it is familiar. Calculate the loss and check the exact cable datasheet before approving it for production.

What RG400 Is Good For

RG400 is usually selected when a buyer wants more reliability headroom than a standard RG58-style cable. Global RF Tech’s GLRG400 is a 50-ohm cable with a PTFE dielectric, FEP jacket, silver-plated stranded conductor, 69.5% velocity of propagation, a -55 to +200 C operating range, and VSWR under 1.25 from DC to 6 GHz, all in the same 4.95 mm jacket diameter as GLRG58. That is why it is often chosen as a same-size upgrade when the cable must run hotter, higher in frequency, or under stricter RF inspection.

In practical terms, an RG400 construction is worth evaluating near heat, under vibration, or when the RF acceptance limits are stricter. For aircraft or vehicle work, cable family selection is only one step: verify the specific cable, connectors, crimp process, strain relief, installation method, and any required compliance documents.

Cable length and frequency decide whether ordinary coax loss becomes a real system problem.

Loss, Frequency, and Cable Length

For RF cable selection, the cable name matters less than the total path loss. A 6-inch jumper and a 6-foot cable can behave very differently even when both are made from the same coax family.

RG58 can work well in short runs. It becomes less attractive when the cable is long, the frequency is high, or the system has a tight link budget. RG400 can provide more headroom, but it is still not a substitute for checking the exact datasheet.

Cable loss (dB) = attenuation (dB/100 ft) × cable length (ft) ÷ 100. Use the metric form if your datasheet is metric: dB/100 m × length in m ÷ 100. Add the specified connector and adapter losses separately.

Run the numbers with the MIL-DTL-17 limits above. A 1 m (3.28 ft) assembly at 400 MHz works out to roughly 0.56 dB worst case for RG58 and 0.34 dB for RG400. At 100 MHz the same 1 m assembly is about 0.21 dB versus 0.15 dB — a difference you will never notice. Stretch it to a 10 m run at 1 GHz and the gap grows to about 0.9 dB, which does show up on a weak receive path.

That leads to the point most buyers get backwards. RG400 is a high-temperature, double-shielded cable that happens to lose a little less than RG58. It is not a low-loss cable. Both squeeze a solid dielectric into a 4.95 mm jacket, so both are limited by physics. If the loss budget is what hurts, the answer is a bigger cable, not a better 4.95 mm cable.

These are engineering estimates from published specification limits, not measured results for a specific assembly. For a long feeder run, compare a larger low-loss family such as LMR-195, LMR-240, LMR-400, RG213, or another cable specified for your actual frequency and environment. Two sanity checks while you do: every 3 dB of cable loss halves the power reaching the antenna, and on receive every 1 dB of feedline loss adds about 1 dB to the system noise figure.

Before you choose, define:

Higher-reliability cable is useful where heat, shielding, vibration or service life matter.

Heat, Shielding, and Mechanical Reliability

RG58 is usually the economical choice for controlled indoor environments. Its common PVC-jacket constructions are easy to source and flexible enough for many short cable assemblies.

RG400 is the stronger candidate when the installation is less forgiving, and the military detail sheet is specific about why: two silver-coated copper braids at 94.8% and 93.6% nominal coverage over a PTFE dielectric, inside an FEP jacket. RG58’s sheet specifies a single tinned-copper braid at 92.8% to 94.2% coverage. Notice what that does not say. The individual braid is not denser. The benefit comes from having a second braid layer and from silver plating that keeps its conductivity as it ages, not from a tighter weave.

RG58 uses one braid; RG400 stacks two inside the same 4.95 mm jacket.

The temperature rating hides a similar detail. RG400 is rated to +200 °C, but PTFE on its own is usually rated for continuous service near 260 °C. The real limit is the FEP jacket, which fluoropolymer producers rate for continuous use at roughly 200 to 204 °C. So the number you check against your engine bay or oven-adjacent routing is a jacket limit, and a cable that lives at the top of that range will age faster than the headline figure suggests.

The jacket, not the dielectric, usually sets a coax cable’s temperature rating.

Braid coverage is a construction detail, not a measured shielding figure. If you need to make an interference-control claim, ask for shielding effectiveness in dB on the exact cable datasheet.

If the cable will sit inside a sealed outdoor box, near an engine bay, behind avionics, close to a transmitter, or in another difficult-to-service location, evaluate temperature, vibration, sealing, bend radius, shielding, and finished-assembly test results together.

Bend Radius Makes RG400 a Drop-In Upgrade

Because both cables share a 4.95 mm (0.195 in) jacket, they need the same routing envelope. That is more useful than it sounds: swapping RG58 for RG400 rarely forces you to re-plan trays, grommets, clamps, or connector back ends.

For a working minimum bend radius, aviation practice is a good reference even outside aviation. FAA AC 43.13-1B tells maintainers to bend RF cables at a radius of no less than six times the cable’s outside diameter. For a 4.95 mm cable that is about 30 mm, roughly the radius of a coffee cup. Cable makers commonly publish 25 mm (1 in) for RG400 itself, so 30 mm is a safe number to design to for both.

A correct bend keeps the dielectric round; a kink shifts the centre conductor off-axis.

Bend tighter than that and the spacing between conductor and shield changes, which changes impedance at that spot. The jacket usually looks perfectly fine afterwards. That is why bend-radius damage tends to appear as an unexplained VSWR bump during testing rather than as visible damage during inspection.

Connector Choice Can Decide the Real Performance

An RG58 or RG400 cable assembly can fail because of the connector, not the coax. BNC, SMA, TNC, FME, N-type, FAKRA, and other connector families all have different frequency, mechanical, and installation requirements.

For a reliable custom cable assembly, confirm:

If you cannot define the connector pair and frequency band, it is too early to approve a cable family.

When RG58 Is Enough

Choose RG58 when the cable is short, the environment is controlled, and cost matters. It is often the practical choice for short antenna jumpers, simple radio cables, bench test leads, internal device wiring, and general-purpose 50-ohm RF links.

RG58 is also useful when the buyer needs fast sourcing and common connector options such as BNC, SMA, TNC, or FME. For many low-risk assemblies, RG58 is the sensible starting point.

Do not use RG58 by habit when the design has a tight RF loss budget, high heat, vibration, or long cable length. In those cases, check the datasheet and compare RG400 or a lower-loss cable family.

When RG400 Is Worth It

Choose an RG400 construction when its documented temperature range, attenuation, shielding, and mechanical properties match a demanding assembly. For aircraft, vehicle, or outdoor equipment, the finished cable assembly must also satisfy the project’s connector, crimp, strain-relief, sealing, vibration, and compliance requirements.

RG400 may be the better choice when the customer already specifies an exact qualified cable for reliability or maintenance reasons. Do not treat the generic RG400 name as proof of certification.

Practical Selection Rule

1. If the cable is a short, low-risk indoor jumper, start with RG58.
2. If the cable sees heat, vibration, or stricter inspection, start by checking an exact RG400 construction. Aircraft and vehicle installations also require project-specific approval.
3. If the run is long or the loss budget is tight, compare a lower-loss family instead of forcing RG58 or RG400.
4. If this is a production assembly, request the cable datasheet, connector drawing, and test report before approval.

Common Questions

Is RG58 the same as RG400?

No. Both are 50-ohm coax cable families, but RG58 is commonly used as a general-purpose RF cable, while RG400 is usually selected for higher-temperature, better-shielded, or more reliability-sensitive assemblies.

Can RG400 replace RG58?

Often yes, if the connectors, diameter, bend radius, and assembly requirements are compatible. The reverse is not always safe, because RG58 may not meet the same heat, shielding, or performance expectations.

Is RG58 50 ohm or 75 ohm?

RG58 is a 50-ohm coax family. If the application needs 75-ohm video or CATV-style cable, RG59 or RG6 may be more relevant, depending on the system.

Is RG58 good for antenna cable?

RG58 can work well for short antenna cables and jumpers. For longer runs, higher frequency, or loss-sensitive systems, compare the actual attenuation table before ordering.

Which cable has lower loss, RG58 or RG400?

RG400, but by less than most people expect. Comparing MIL-DTL-17 limits for both, RG400 is about 6.5 dB/100 ft better at 400 MHz and 11 dB/100 ft better at 1 GHz. On a 1 m jumper that is a fraction of a decibel. Choose RG400 for temperature, shielding, and frequency headroom rather than for loss alone.

Is RG400 the same as LMR-400?

No. RG400 is a 4.95 mm PTFE cable; LMR-400 is a 10.3 mm foam-dielectric cable with far lower loss, different connector hardware, and a much larger bend radius. The shared number is a coincidence.

Is RG58 still a current military specification?

Not for new designs. The MIL-DTL-17/28 detail sheet for M17/28-RG058 has been inactive for new design since 1993. Commercial RG58 is still produced in volume, so ask the supplier which datasheet the cable is actually built to.

Which connectors are common for RG58 and RG400?

Common options include BNC, SMA, TNC, FME, N-type, and other RF connector families. The correct connector design, crimp process, and strain relief matter as much as the cable family.

Conclusion

RG58 is the practical choice for short, low-cost, general-purpose 50-ohm RF cable assemblies. An RG400 construction is the stronger candidate when its documented heat, vibration, attenuation, shielding, and inspection performance matches the requirement.

For a custom RF cable assembly quote, send the cable family, connector pair, length, frequency band, environment, target loss, test requirements, and expected quantity. That information lets an engineering team recommend whether RG58, RG400, or a lower-loss alternative is the right starting point. Browse our RG58 coaxial cable and RG400 coaxial cable. For termination choices, use our antenna connector types guide; for miniature cable selection, see RG174 vs RG316.