My first 10BASE5 network segment

Pete Turnbull pete at
Fri Aug 26 05:34:47 CDT 2016

On 26/08/2016 06:26, Warner Losh wrote:
> 10base5 also had rules for minimum bend radius

True, because bending the cable alters the geometry and introduces 
impedance discontinuities, though (to be picky) the allowable bend 
radius varies between cable manufacturers because the precise cable 
construction dictates the tightest bend that wouldn't upset the 
impedance.  What I recall from the standard is that cables must support 
a bend radius of 254mm /or less/ in order to be flexible enough for 
reasonably easy installation.  A sort of "maximum minimum bend radius".

> as well as tap locations to be at the maxima of the reflection point.

Actually it's to /avoid/ maxima and thereby to ensure things are out of 
phase, minimising adverse interference effects.  The node positions are 
at 2.5m intervals, a distance which is chosen so that taps and 
terminators are very unlikely to be exact wavelengths apart and hence 
will /not/ be at maxima, so conflicting signals will be out of phase. 
IIRC correctly it's deliberately not quite 1/19th of the wavelength.

For the same reason, cable sections are supposed to be odd multiples of 
the half-wavelength of the signal (23.4m, etc).

> For early gear, failure to
> put it at a vibration node would often result in unreliable behavior, though
> I can't recall if that included collisions or not.

Pete Turnbull

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