> I've handled many hundreds of reels of Heliax over decades, and never
> worried much about that warning, which has more to do with
> creating egg
> shaped cable (from the weight of the upper layers) than to center
> conductor migration. Heliax is very robust. Measure the impedance if
> you'd like, but I'd bet that it's still perfect if it's been kept dry.
>
> -Steve K8LX
Right-O. It has nothing to do with migration of the center conductor, but
rather deformation of the shield. If the reels if LDF were laid down gently
(as opposed to being flopped on its side as what typically happens at a
freight depot to make it easier to move around with a forklift), it should
be OK. Even if there are a few flat spots, the eccentricity is usually not
enough to make that huge of a difference in Z0.
In broadcast, digital cellular, and other applications where very low VSWR
is important, a flat spot would result in the reel being rejected, but for
ham use, it's a matter of what you're willing to tolerate. Sweep it with a
TDR/FDR and see what it looks like.
FYI, newer cables with much-thinner shield material such as Andrew AVA
series are MUCH easier to dent/flatten. If a reel of AVA comes in laying
flat, it gets rejected without even bothering to unwrap it.
--- Jeff WN3A
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