[time-nuts] Thermal effects on cables

jimlux jimlux at earthlink.net
Mon Jan 23 15:00:33 EST 2017

On 1/23/17 7:13 AM, REEVES Paul wrote:
> Hi David,
> Surely the impedance of the cable is only affected by the ratio of the inner conductor and outer conductor diameters modified by the internal dielectric constant, nothing to do with the frequency of operation. You might well have problems converting the larger diameters down to a suitable size for the connectors at the higher frequencies though....
> I thought that the HP cabling for the 8510 series VNAs was air spaced but I might well be wrong - I just tried not to damage them :-)
> Regards,

I think the large outer diameter is essentially a soft armoring, which 
limits the bend radius, which in turn limits the deformation of the 
outer conductor and dielectric.

VNA test port cables also have very good shielding effectiveness as well 
as stable propagation properties.

The underlying cable would have to be fairly small diameter, because 
otherwise you'd get moding problems at high frequencies.  At 60 GHz, the 
cable really has to be smaller than a few mm diameter.

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