[BC] Wave lengths

[Jeff Johnson]

>
>so, you should be able to use the numbers for the 'velocity factor' to 
>know pretty closely where the wave multiples are in any coax you've got 
>the velocity factor for (if you know the f(mhz)...
>
>   Have I got it so far?

Sure seems like it!

>    So, does the negative part (the ground shield) of the coax have other 
> weirdness where it meets the (usually) black outer cover??  Seems like 
> that conductor has two junctions, one inner (foam) and one outer (black stuff).
>??  How come half the wave isn't slowed down more than the other??

There is no RF on the outside of the coax. (At least not the RF under 
consideration!) The outside of the outer conductor is not a factor.

>   I could see how ladder line (balanced, parallel lines held apart by 
> insulators...) would have the same 'velocity effecting' factors, since 
> they're both out in the air... but in normal 'unbalanced' coax, it would 
> seem the outer conductor has a junction with insulation the inner 
> conductor doesn't have... so is there a difference you can see by 
> comparing those signals, if you know what to look for...?
>Or is the 'velocity factor' sort of a combination of all the above... ?
>
>Jason

The velocity factor differs due to the dielectric coefficient of the 
insulator. Think of it as the RF having to charge and discharge capacitance 
(the distributed capacitance) of the line. The higher the capacitance 
(vacuum<air<foam<solid) the more 'work' the RF must do traveling the coax 
and it takes longer doing it. Think of running on the street vs. running on 
the beach (as explained by another here recently). That is why an open 
'ladder line' and an air dielectric coax have high velocity factors - less 
distributed capacitance and the RF can 'run' faster.

Jeff.Johnson at goodnews.net