[time-nuts] Data collection cycle -- multiple sources to one counter?
david.kirkby at onetel.net
Sun Jun 19 09:37:21 EDT 2005
Brooke Clarke wrote:
> When working with the HP 4380S Balanced Network Analyzer system I found
> that using flexible cables resulted in an unstable system. My first
> improvement was to use 0.141" semi rigid coax (it's much more on the
> rigid side) and got a mandrel to bend it. Later I discovered you can
> get flexible 0.141" coax that's not "rigid" and it worked great, no
> mandrel needed. The point is that you probably will need to have good
> control on all the coax lines. The lines will change length with
> temperature, so the longer they are the more temperature variation there
> will be.
If its not moved, is semi-rigid any more stable than other coaxes, if
its not moved?
I don't know all the mechanisms for delays in coax, but the temperature
coefficient of the dielectric constant of the dielectric must be one of
them, and quite possibly the most significant. I would have thought that
dominated any change due to the expansion of the metal. This would
suggest you need to find the optimal dielectric.
I've got a bit of cable here with what is basically an air dielectric,
with the inner conductor supported on a spiral of some sort, which means
99% of the dielectric is air. However, that cable is not practical at
PTFE might for example be a lot better/worst than polyethylene in the
variation of dielectric constant with temperature.
I'm not sure that RG405 semi-rigid (which is what I guess you mean) is
necessarily the best choice.
I used semi rigid a lot, but prefer the bigger one, since its a lot
easier to solder, as my eyses can see it!!
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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