[time-nuts] Non-impedance matched antenna cables

[Richard W. Solomon]

Sounds like an application just calling for "hard line". I have some 75
foot lengths of 1/4" Superflex that I'll have to drag out and look at.

73, Dick, W1KSZ

-----Original Message-----
>From: Mark Sims <holrum at hotmail.com>
>Sent: Jun 13, 2008 5:37 PM
>To: time-nuts at febo.com
>Subject: [time-nuts] Non-impedance matched antenna cables
>
>
>A while back I did a project that used a 100 foot piece of (supposedly) fairly good quality RG58.  I checked it with my TDR and then installed it in an outdoor application where it ran for a couple of weeks in good ole' Texas weather.  The outdoor connection was covered by a glass jar so water infiltration of the connector was not an issue.  Also the cable was not hanging, so stretching under its own weight was probably not an issue.  
>
>When the project was then over I happened to check the cable with the same TDR.  Its effective electrical length had changed by around a foot!   A half-wave of GPS is around 4 inches.  I think that most commercial coax is way too unstable to maintain that kind of precision in a real-world installation.  A .2% shift in velocity factor or cable length in a typical 100 foot run would be 1/4 wave of GPS signal.
>
>> ----------------------------------------
>>   
>Depends on the cable length and the temperature excursions it experiences.
>For short runs its well worthwhile.
>For longer runs the cable attenuation will help reduce the effect of 
>mismatches at either end.
>
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