[TowerTalk] superflex for rotor loop?

[Bob Nielsen]

On Apr 30, 2006, at 5:28 AM, <radio_k4rv at peoplepc.com>  
<radio_k4rv at peoplepc.com> wrote:

> Is Andrew 1/2 inch superflex continuously flexible enough to be  
> suitable for
> use as a rotor loop?


No.  Use coax with a braided shield and stranded center conductor  
instead.  It will flex fine for a while, but eventually the  
corrugated copper outer conductor and/or the solid center conductor  
will fail.

About 30 years ago I was working on an application for feeding an  
antenna on a gimballed platform at Hughes Aircraft and we were  
concerned about the effects of flexing the coax.  We did a life test  
where we continuously flexed the cable and measured return loss,  
looking for changes.  We first tried RG-142B, which had a copperweld  
center conductor.  After several hours it failed and the autopsy  
showed that the copperweld had broken into several small pieces in  
the region being flexed.  We tested again with RG-400, which is  
similar except that it has a stranded copper center conductor and  
that was still going fine after several hundred hours of flexing.

73,
Bob Nielsen, N7XY