Published on 10/13/2026
RG142 and RG400 are nominal 50 Ω coaxial cable families commonly built with PTFE dielectric, FEP jacket and two silver-plated copper braids. A key difference in common constructions is the center conductor: solid silver-plated copper-clad steel in RG142, versus stranded silver-plated copper in RG400. Exact ratings still come from the selected cable part.
A +200 °C cable can be part of a high-temperature interconnect, but a sleeve, adhesive or connector may fail well before that temperature. Choosing high temperature coaxial cable is only the first step. The finished assembly and installation need their own limits.
This guide compares reference RG142 part 83242 with one documented RG400 construction. It does not merge vendor ratings into a universal spec. SigmaRF can agree the cable, connectors, routing and tests required for a repeatable build.
On This Page
| Property | RG142 reference 83242 | RG400 reference construction |
|---|---|---|
| Center conductor | 19 AWG solid silver-plated copper-clad steel | 19-strand silver-plated copper |
| Dielectric / jacket | PTFE / FEP | PTFE / FEP |
| Nominal diameter | 4.95 mm | 4.95 mm ±0.1 mm |
| Shield | Two 95% silver-plated copper braids | Silver-plated copper braids, 97% and 94% |
| Impedance | 50 Ω nominal | 50 Ω ±2 Ω |
| Velocity / capacitance | 70% / 95 pF/m | 69% / 94 pF/m |
| Operating temperature | -70 °C to +200 °C | -65 °C to +200 °C |
RG400's stranded conductor may be useful where routing and handling favor that construction. RG142's solid copper-clad steel conductor is a different mechanical and electrical choice. Neither family name proves continuous-flex endurance or precision phase stability. Use the exact connector approval and cable preparation requirements.
Key idea: FEP is the jacket material; PTFE is the dielectric in these references. Calling both simply "Teflon coax" hides the construction and can obscure the part-specific qualification needed.
High-temperature cable ratings do not automatically rate the completed assembly. The connector dielectric, contact system, strain relief, heat-shrink, adhesive and mounting environment can narrow the range. Specify the assembly operating conditions and obtain the appropriate component evidence.
| Rating | RG142 reference | RG400 reference |
|---|---|---|
| Operation | -70 °C to +200 °C | -65 °C to +200 °C |
| Installation temperature | Use the approved cable instructions | -20 °C to +60 °C |
| Bend radius | 51 mm minimum installation | 30 mm static; 50 mm repeated |
| Qualification | Commercial non-QPL, M17/158-00001 reference | Verify source/qualification separately |
| Environmental claim | Reference cable lists CMP/plenum and UV suitability | Jacket and flame properties need exact-part review |
Do not merge the lower temperature limits into a single family rating, and do not assume all FEP-jacketed cables have the same fire approval. One reference lists plenum suitability; that is evidence about that particular cable, not every RG142 assembly or every RG400 variant.
⚠️ An operating rating of +200 °C is not a solder-process recipe. Follow the connector assembly instructions and verify materials used at the termination. A heat-damaged dielectric can pass continuity and still fail the RF sweep.
The following nominal attenuation points belong to the reference RG142 cable. They are converted using 100 ft = 30.48 m. They are not RG400 loss data and not maximum finished-assembly insertion loss.
| Frequency | RG142 nominal dB/100 ft | Converted dB/m |
|---|---|---|
| 100 MHz | 3.8 | 0.125 |
| 400 MHz | 6.9 | 0.226 |
| 1000 MHz | 13.1 | 0.430 |
| 2000 MHz | 19.3 | 0.633 |
| 3000 MHz | 24.2 | 0.794 |
| 5000 MHz | 32.6 | 1.070 |
| 8000 MHz | 43.2 | 1.417 |
At 1 GHz, this reference is approximately 0.430 dB/m. A 0.5 m length contributes about 0.215 dB before connector effects. Request the exact RG400 part's attenuation instead of assuming that same number because its diameter is similar.
The selected RG400 reference explicitly states operation to 6 GHz. The RG142 attenuation table includes an 8 GHz point, but a table point alone does not rate every connectorized assembly to that frequency. Cable, connectors, terminations and the agreed acceptance sweep set the usable product band.
Operating voltage and dielectric test voltage are different. The RG400 reference lists up to 1.7 kVrms operating at sea level and 3.4 kVrms test at 50 Hz for 1 minute. These are cable-only conditions, not universal RF power limits. Never infer assembly watts from a withstand-voltage line.
Choose between RG142 and RG400 by construction, loss budget, required environment and approved interfaces. A stranded conductor is not inherently lower loss, and a solid conductor is not inherently more phase-stable after every bend.
Temperature-constrained routingEquipment interconnectsRF fixturesScreening-sensitive assemblies
Consider RG142
The approved solid-conductor reference fits fixed routing, temperature and RF acceptance requirements.
Consider RG400
The approved stranded-conductor construction fits handling and routing, with its own loss and environmental data verified.
For repeated movement, define a flex qualification. For timing or phase matching, define electrical-length limits and measure them. For harsher environments, verify the exact jacket and sealing requirements. SigmaRF's flexible versus semi-rigid guide and shielding guide explain alternative constructions and assembly-level screening.
Specify the complete RF assembly
Send the frequency band, connector interfaces, finished length and routing drawing. SigmaRF can match the cable and terminations to your application.
Step 01
Name the cable and connector parts
Specify RG142 or RG400 by approved part, conductor construction and source requirements. Choose compatible connector cable groups, polarity, body style and terminations.
Step 02
Define routing and materials
Show finished length, datums, tolerance and bend geometry. Specify the temperature exposure, strain relief and any sleeves or adhesive. The cable jacket should not be the only rated component.
Step 03
Set electrical acceptance
Give VSWR and insertion-loss limits over the operating band, reference planes and reporting needs. Insulation/hipot tests and environmental qualification are additional checks, not replacements for an RF sweep.
SigmaRF VNA-sweeps every assembly for VSWR and insertion loss before shipment. Its overall RF assembly capability spans 100 MHz to 40 GHz across suitable cable and connector systems, not every product discussed here. Volume work is supported in Vadodara, India, with precision work in the Cleveland area, USA. Lead times can be as short as 2 days for suitable builds, subject to parts, quantity and the agreed specification.
SigmaRF's company capability is not a universal 40 GHz rating for RG142 or RG400. For repeat orders, retain the approved drawing, component parts and test limits. Use the RF assembly design and VNA measurement guides to define the mechanical and measurement details.
Assume a 0.5 m RG142 assembly at 1 GHz using reference nominal attenuation of 13.1 dB/100 ft. Add a hypothetical 0.05 dB for each connector. This estimate is not measured SigmaRF performance or a production maximum.
Cable attenuation = 13.1 / 30.48 = 0.430 dB/m
Cable contribution = 0.430 x 0.50 = 0.215 dB
Estimated matched-path loss = 0.215 + 0.05 + 0.05 = 0.315 dB
Matched power ratio = 10^(-0.315/10) = 0.930, about 93.0%
Temperature and actual terminations can change the result. If the drawing calls for a maximum loss across a band at elevated temperature, room-temperature nominal arithmetic is insufficient. Define a test or evidence basis that covers the application rather than applying the cable rating as a blanket guarantee.
Avoid misleading high-temperature claims
Before procurement
What is the difference between RG142 and RG400?
Common RG142 uses a solid silver-plated copper-clad steel conductor; common RG400 uses stranded silver-plated copper. Both references here use PTFE dielectric, FEP jacket and double braid, but exact ratings remain part-specific.
Is RG400 rated to 200 °C?
The selected reference lists operation from -65 °C to +200 °C. That does not rate the connector, sleeve or completed assembly to the same range. Verify the whole material stack.
What is RG142 signal loss at 1 GHz?
Reference 83242 has nominal attenuation 13.1 dB/100 ft, about 0.430 dB/m, at 1 GHz. Connectorized assembly loss needs its own measurement and maximum limit.
Are RG142 and RG400 both double-shielded?
The reference constructions each have two silver-plated copper braids. Check the exact cable and any required assembly screening measurement rather than inferring dB effectiveness from braid count.
Can RG400 be used at 6 GHz?
The selected reference states operation up to 6 GHz. The complete assembly still needs suitable connectors and agreed VSWR/insertion-loss limits across the actual band.
Can SigmaRF make high-temperature coax assemblies?
Provide the approved cable, connector interfaces, temperature exposure, routing and electrical limits. SigmaRF can agree the build and test requirements; confirm every termination material fits the application.
RG142 and RG400 can fit high-temperature RF work when their exact construction and limits are understood. Their similar jacket and diameter do not make them electrically or mechanically interchangeable.
Select the full assembly, define the environment and verify the RF result. A precise drawing and component evidence are better protection than a broad "FEP high-temperature coax" label.
Build an RF assembly around the real requirements
Send the frequency band, connector interfaces, finished length and routing drawing. SigmaRF can match the cable and terminations to your application.