[time-nuts] Comparing PPS from 2 GPS units

Jim Lux jimlux at earthlink.net
Tue Dec 18 05:52:00 UTC 2012

On 12/17/12 9:40 PM, Hal Murray wrote:
> jimlux at earthlink.net said:
>> You mean RG65 http://www.awcwire.com/ProductSpec.aspx?id=M17/
>> 34-RG65-Coaxial-Cable or RG186 http://www.awcwire.com/ProductSpec.aspx?id=RG1
>> 86-Coaxial-Cable
> Interesting stuff.  Thanks.
> RG-65 says no longer available.  It also says:
>    Coaxial Delay Line 0.15 uSec/ft
> (Am I having troubles counting zeros, or is that seriously slow?)
Yes, seriously slow.. 150 ns/ft, vs 1ns/ft in free space..

>    Nom. Imp.  	950
>    Vel. of Prop.  	2 (no units)
>    Cond. Material  	Magnet Wire Helix
> (What is "magnet wire", and what does "helix" mean and how does it effect
> coax?)
> RG186 says:
>    Shield Material  	Magnet Wire   [What does that mean?]
>    Nom. Imp.  	1000
> The cable on scope probes (at least fancy ones) has a tiny conductor.  I
> think that translates into high impedance.

No.. this stuff has a helically wound center conductor (so the L per 
unit length is very high).. impedance is sqrt (L/C) so the Z is high 
(1000 ohms).. prop velocity is 1/sqrt(LC), so big L means slow prop..

This stuff is incredibly lossy..

Some of it has the center conductor wound around a soft iron core wire 
to increase the inductance.


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