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Elaborate on semi-steel cables

Author: Date:12/13/2019 12:14:48 AM
  The application of semi-steel cables is very wide, and we all know that its biggest advantage is that it has excellent shielding. Therefore, the choice of upper half-steel cables in many instruments, equipment, military products and other systems is the designer's favorite. With the development of science and technology, the speed of product upgrades continues to increase, and the application of semi-steel cables has declined. The main reason is that semi-steel cables can only be formed at one time and require high bending accuracy. In this way, for some batch-type products (products with faster iteration), semi-steel cables can only be helplessly dropped, and semi-flexible cables have become a new favorite. Regardless of the development of science and technology, at present, semi-steel cables still have their place. Let's analyze it below.

Judging from the types of semi-steel cables that are currently produced, production can be performed in various possible sizes and almost all impedances.


Standard 50Ω cable

Cable diameters from 0.6mm to 10mm can be produced.


Stable semi-steel cable

   At present, the semi-steel cable insulation materials supplied on military products use a special solid polytetrafluoroethylene (PTFE) dielectric. Compared with traditional solid PTFE semi-steel cables, the thermal stability is significantly improved. The improvement in thermal stability reduces the need for temperature pretreatment, and almost eliminates the protrusion of the electrolyte during front welding. All other mechanical and electrical properties are equal to or better than traditional solid PTFE similar cables.


Low-loss half-steel cable

Modified semi-steel cables usually reduce attenuation by 20% and increase the operating temperature to 250 ° C.


Non 50Ω impedance cable

Impedance 5 to 100Ω, diameter range 0.6mm to 6.35mm


I. Structure of semi-steel cable


Inner conductor

   The inner conductor is usually silver-plated copper or silver-plated copper-clad steel. Silver plating is not only an excellent conductor, but also prevents oxidation during the manufacturing process and improves the solderability of the finished cable.



The most commonly used dielectric for insulation is polytetrafluoroethylene (PTFE)


   The insulating material between the conductor core and the outer conductor maintains the spacing and geometry in the cable, ensuring mechanical integrity during forming and bending. Most transmission losses are directly or indirectly caused by the dielectric. Although cables with low dielectric constant provide lower bulk dielectric losses, larger conductor core diameters are required to maintain the same characteristic impedance. The larger conductor core can significantly reduce the overall attenuation of the cable. In addition, the dielectric determines the propagation rate, temperature range, rated power, phase and amplitude stability, and affects the flexibility of the cable.


Outer conductor

The most common outer conductor material is copper (bare copper tube or ternary alloy copper tube)

There are many uses for outer conductors. Outer conductors are electrical shields that affect cable attenuation and control RF leakage.


2. Characteristics and advantages of semi-steel cables


   Semi-steel coaxial cables are available in a variety of sizes, materials, and characteristic impedances. Only cables with solid metal tubes as outer conductors can be called semi-rigid coaxial cables. Most of the semi-steel cables currently supplied do not exceed 6.35mm in diameter, but some selected cables can be as large as 10mm. Silver-plated copper conductors and PTFE dielectric and copper tube outer conductors are the most commonly used materials. The impedance ranges from 5 to 100Ω. Typical maximum temperature can reach 125 ° C to 250 ° C


RF shielding exceeds 120dB

Minimal attenuation and lightest weight for any given geometry

Unmatched impedance control and standing wave performance

Minimal outer diameter in microwave cables

Very small bend radius can be used for the densest wiring

The environment is sealed and there is no need to worry about the sheath being cut or worn


3. Typical applications of semi-steel cables


The application frequency of semi-steel cables is from very low to 110GHz.

Almost all systems that operate above 500MHz and require good operating performance and full shielding should choose semi-steel cables, including defense electronics, test and measurement instruments, aerospace systems, and other precision applications. Among the components, semi-steel cables are used for oscillators, amplifiers, printed circuit boards, delay lines and capacitors.