Learn from an experimental physicist

Feb 19, 2015 learning coax phys-332

dimension of LMR-195 coaxial 


Structure of a coaxial cable, coax in short, from inside out: core wire, dielectric insulator, 1 or several layers of metallic boil, mesh or braid, outer sheath or jacket. The top figure shows the dimension of a typical coax.

One layer of braid can block 95% of external interference with an approximate shielding effectiveness of -55 dB. The left 5% can be blocked by adding extra layers of foil with an approximate shielding effectiveness of -90 dB.

Commonly used coax

RG, Radio Guide coax. Old military standard. Commonly used ones:

  • RG-59, RG-6, RG-11 from low end to high end uses, impedance: 75 Ohm, outer diameter: 6.1, 6.86, 10.5 mm, respectively. Used with F connectors for TV
  • RG-58, RG-142 from low end to high end uses, impedance: 50 Ohm, outer diameter: 5, 4.95 mm, respectively
  • RG-316/U, RG-174, impedance: 50 Ohm, outer diameter: 2.6 mm, single shield, used with LEMO 00 connector

LMR, nobody knows what it stands for. Made by Times Microwave Systems. Low loss coax, 50 Ohm.

  • LMR-100A, outer diameter: 2.79 mm, replace RG-316/RG-174
  • LMR-195, outer diameter: 4.95 mm (0.195 inch), replace RG-58, RG-142


LEMO 00, Leon Mouttet connector. Miniature push-pull 50 Ohm coaxial connector. Replacement of BNC in high density design, front panel connectors for NIM & CAMAC modules. Diameter: ~ 5 mm.

BNC, Bayonet Neill Concelman connector. Diameter: 14.5 mm (Male), 11.1 mm (Female). Passband: 0-4 GHz. Impedance: 75 or 50 Ohm. The 75 Ohm types can sometimes be recognized by the reduced or absent dielectric in the mating ends.

SHV, Safe High Voltage (>500V) connector. Up to 5 kV DC, 5 A. 20 kV version also available.

MHV, Miniature High Voltage (>500V) connector. Up to 5 kV DC, 3 A. Easily mistaken as BNC.

MCX, Micro CoaX connector. Diameter: 3.6 mm. Passband: 0-6 GHz. Impedance: 75 or 50 Ohm. Gold plated. Snap-on interface.

SMA, Sub-Miniature version A. Diameter: 7.9 mm. Passband: 0-18 GHz.
Impedance: 50 Ohm. Screw coupling.

F connector, for TV. Cheap because core wire of cable is used as pin of male connector. Diameter: 11 mm. Passband: 0-1 GHz, Impedance: 75 Ohm.


Normal cutters with flat blades cannot keep a round cross section of the cable after cutting. Special cutters have to be used for coax.


It is sometimes called coax prep tool, stripping tool, etc. Some of them have 2 blades, some have 3 blades. This feature is labeled as 3-blade, 3-level or 3-step. The stripping distances of 3-blade ones are normally 4 mm of dielectric, 8 mm of braid. Normally, the cutting depth of the blade is adjustable with an Allen wrench. Some strippers can be used for cables with various outer diameters. Some are designed just for cables with similar outer diameters. For example, HT-312B is a 3-blade stripper for cables with diameters about 5 mm.

Coax connector crimper

It normally has a frame with exchangeable dies. A die may have hexagonal cavities with different diameters.


Blogs on physics research and educational activities of Jing LIU, an assistant professor in physics at the University of South Dakota. He is an experimental physicist developing novel particle detectors for astroparticle physics and civil use.


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