Sherrill WATKINS wrote:
>
> John: The fact that your swr changes when it is raining indicates that loss
> (attenuation) is occurring somewhere in your system. - 73's- Corn- k4own.
>
Not necessarily true. SWR changes can come from changes in dielectric
constant, not changes in loss. Changes in dielectric constant along a
feed line will change its characteristic impedance. Clean rain water can
be that added dielectric. The dielectric can become lossy if near a
water molecule resonance. At 440 MHz, water leaking into an air spaced
coax generally improves the SWR, but increases the line losses
significantly. At other frequencies water simply as a dielectric can
change the match on a beam, ice is far more effective at changing the
impedance match. Two days ago my long 144 MHz packet beam quit working
with only 1/8" of ice or less. Couldn't work the path until the ice
melted. Different beam designs have different tolerances for water.
K1FO's do the best, at least according to K1FO.
Water can also add losses by wetting insulators made of PC boards or
covered by dirt.
73, Jerry, K0CQ
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