[time-nuts] Galvanic decoupling of GPS antenna

jimlux jimlux at earthlink.net
Fri Jun 18 17:46:48 UTC 2010

Robert Benward wrote:
> Rated for 1400V from CENTER conductor to shield, not shield to the 
> outside. If you choose to use RG-58 with 250V on the shield then you 
> will need to put the entire cable inside conduit.  It is not acceptable 
> to have any type of exposed mounting.
> Bob

Yeah... I've been looking for the jacket rating...  As a practical 
matter, I've used solid dielectric RG-58 (both A and C flavors) to carry 
10kVrms AC (neon sign transformer type voltages).  Usually, you don't 
get breakdown between center/shield.

However, considering that ordinary PVC insulated hookup wire is rated at 
300V, I suspect it's ok.

Obviously, we're talking a transient here.. if you're floating the 
shield at 200V above surrounding objects/ground, a better solution is 
called for.

Interestingly, looking at MIL-C-17 (which covers coax)

There are several requirements for RG-58 (MIL-C-17-28)
Spark test: 5000V rms +10%/-0%
Voltage Withstanding: 5000Vrms +10%/-0%
Corona extinction voltage 1900Vrms minimum

Then, looking at the test procedures in Sec 4.8 of MIL-C-17G

Spark test (4.8.3) A test voltage at a frequency...shall be applied 
between the outermost braid or shield and the outer surface of the jacket.

Voltage withstanding (4.8.4) (a) For coaxial cables. The test voltage 
shall be applied between the inner and the outer conductor, with the 
outer conductor grounded.

Overall.. MIL-C-17 is a great reference on how to test coax (or to ask 
your coax supplier about how they test...)

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