On 10/19/2010 12:27 PM, Andy wrote:
> It would seem, then, that twisting one's ladderline might help.
YES!
> One might envision even using twisted wire pairs instead of open
> ladderline. But with such tight coupling, comes (a) much lower cable
> impedance (100 ohms or less), and (b) higher loss, probably closer to
> that of coax since most of the dielectric wouldn't be air anymore.
The primary component of loss below UHF is copper loss, not dielectric
loss. Most of the reduced loss of parallel wire lines is the higher Zo
due to wider spacing. The higher Zo means less current, and the loss is
I squared R.
There's at least one exception to this. A decade or so ago, N7WS did
some research, published in one of the ARRL Antenna Compendiums, showing
that WINDOW line gets pretty lossy when it gets wet. That is, of course,
dielectric loss. Likewise, water in coax is likely to greatly increase
dielectric loss.
73, Jim K9YC
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