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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
Well in the first example the minimum bend radius is specified as 50mm, and in the product for sale on ebay it's 4 inches (approximately 100 mm); so right there you have a 2:1 difference between the two items which are both called RG213 and look to be physically identical.
I meant that yes your right none of the specs differ, only the bend radius, I would just say buy the smaller bend radius one.
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Since they don't specify how they came up with the number assume the worst which is that it is the mechanical failure specification. The electrical specs may be fine at that bend radius... or they might not be.
You'd probably have to call the seller or buy somewhere else if you want to know for sure. Or buy one and test it yourself.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Mattski wrote ...
Since they don't specify how they came up with the number assume the worst which is that it is the mechanical failure specification. The electrical specs may be fine at that bend radius... or they might not be.
You'd probably have to call the seller or buy somewhere else if you want to know for sure. Or buy one and test it yourself.
The seller likely wont know a dam thing, its the maker that he needs to call.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The RG series began life as cable specifications defined in MIL-HDBK-216.
MIL-HDBK-216 is no more, but the widespread industry acceptance and confidence in the RG specs lead to their continued use as less closely defined 'types.'
The original mil spec might have called for costly silicone rubber sheathing, and PTFE dielectric, while the RG clone may maintain the same general electrical properties but be made of less costly materials like PVC to meet the needs of the consumer mass market - TV reception, for example.
On the minimum bending radius, coax manufacturer PIC says:
Bending, stretching, and kinks can force the center conductor to one side. This disturbs the common axis of the conductor and shield — they are no longer concentric — and shows up as a change in impedance at the point of "injury." This can actually be seen on a Time Domain Reflectometer (TDR), an instrument which examines cables for signal reflection, appearing as an electrical "bump" (or dip).
The penalty for mishandling comes in increased losses, reflection quirks and impedance mismatches translating to higher VSWR (Voltage Standing Wave Ratio), and instability of other characteristics. Any of these can have a serious effect on overall system performance.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Normally when electricians install wire and cable the general rule of thumb is bend radius (max) is equal to 5 times the diameter of the wire or cable. You can actually look up the specifics in the national electric code book. Control panels are often designed by engineers keeping the 5x diameter rule in mind. Bend radius is simply to protect the shielding or insulation from crinkling up in the inside of a bend and thinning on the outside of a bend, causing it to be useless. Also to keep from stretching conductor material (usually copper) to a point that could break it, or stretch it thinner and decrease ampacity.
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