Armored Cable
Understanding Armored RF Cables
In a combat vehicle, the coaxial cable connecting the antenna to the radio travels through an environment that would destroy ordinary cabling in days: intense vibration, extreme temperatures, repeated flexing as hatches open and close, and potential impact from debris. Armored RF cables are engineered specifically to maintain signal integrity in these conditions while physically surviving the mechanical punishment of military service.
Construction Layers
An armored military RF cable is a precisely engineered multi-layer structure:
- Center conductor: Silver-plated, stranded copper for flexibility and corrosion resistance.
- Dielectric: PTFE or cellular PTFE for low loss and temperature stability.
- Outer braid shield: Silver-plated copper braid at high coverage (>95%) for EMI shielding.
- Armor layer: Interlocked stainless steel armor spiraled over the outer jacket.
- Outer jacket: Abrasion-resistant polyurethane or PTFE jacket for environmental sealing.
The Trade-off: Weight vs. Protection
Armor adds significant weight and stiffness to the cable assembly. A 20-foot armored N-type RF cable assembly for a combat vehicle radio may weigh 4–6 kg. Modern armored cables use Kevlar braid in combination with lighter stainless spiral to reduce weight while maintaining crush and cut resistance. This SWaP optimization is critical in weight-sensitive airborne applications.
Key Equations
An Armored RF Cable is a coaxial cable assembly that incorporates one or more mechanical protection layers — typically a stainless steel or galvanized steel...
Key specifications:
55 °C | 125 °C | 95 % | 6 k | 0 dB | 1 mW
Power: P(dBm) = 10log(PmW), 0dBm = 1mW
Comparison
| Connector | Freq Max | Impedance | Power | Interface |
|---|---|---|---|---|
| SMA | 18 GHz | 50 Ω | 0.5 W | Threaded |
| N-Type | 11 GHz | 50 Ω | 5 W | Threaded |
| 2.92mm (K) | 40 GHz | 50 Ω | 0.3 W | Threaded |
| 1.85mm (V) | 67 GHz | 50 Ω | 0.2 W | Threaded |
| 1.0mm (W) | 110 GHz | 50 Ω | 0.1 W | Threaded |
Frequently Asked Questions
Does armor affect RF performance?
The armor itself does not directly affect RF performance, because it is outside the outer jacket and not in the RF signal path. However, the increased cable diameter and stiffness can increase bending radius requirements, affecting connector interface reliability at repeated flex points. Additionally, the heavy outer armor can create ground loop issues if it makes inadvertent metallic contact with vehicle chassis at multiple points, potentially creating conducted interference paths.
What is MIL-DTL-17 and why does it matter?
MIL-DTL-17 is the US Department of Defense specification that defines the performance and qualification requirements for coaxial cables for military use. It specifies electrical parameters (impedance, attenuation, VSWR, shielding effectiveness), environmental performance (temperature range, humidity, vibration), and testing methods. Cables complying with MIL-DTL-17 dash numbers have been independently tested against these specifications, providing a trusted baseline for military procurement without requiring costly re-testing of each cable lot.
How are armored cable connectors installed?
The armor layer must be terminated before attaching the RF connector. Terminating steel armor requires specific tools: a cable cutter that cleanly cuts the steel without unraveling the interlocked spiral, and crimping or clamping hardware that mechanically captures the armor end. Improper armor termination — leaving sharp steel ends near the dielectric or outer shield — is a common cause of field cable failures, as the steel spirals abrade through the outer shield over time under vibration, causing progressive shield contact degradation and increasing insertion loss.