I'd suspect some kind of bad connection due to thermal expansion.
Moisture is not likely to make that kind of dramatic shift in SWR, and
certainly not that consistently from day to day.
73,
Dave AB7E
On 4/1/2012 8:01 AM, Richard Thorne wrote:
> I finished my tower/antenna install Friday. 77' of 45g with 15' of mast
> out the top. I have a F12 D240 mounted 10' up the mast and a F12 C31 at
> about 1' up the mast. The swr is where they are supposed to be on both
> antennas.
>
> Now for the strange part.
>
> Some time after dark my D240 becomes attenuated and the swr is very very
> high. But after the sun comes up for about 2 to 3 hours, the
> attenuation goes away and the swr is right where its suppose to be and
> signals are clear and strong.
>
> Its been clear with no rain since the antenna has was put up Friday
> morning. There must be some moisture in the air as dew does form on the
> grass and the roof of my steel building/shop.
>
> So I'm scratching my head on this one. I've switched out coax cables at
> the shack, bypassed the polyphaser lightning suppressors, used the
> different antenna inputs to my Elecraft K3, checked to be sure I didn't
> have a receive antenna selected on the K3 etc.
>
> I have a single 158' run of coax from my entrance panel to the top of
> the tower and have it terminated with one of these
> http://www.dxengineering.com/Parts.asp?ID=3320&PLID=105&SecID=94&DeptID={DBD52E00-E4FA-4BB0-A7B9-1EDCD8FCDE17}&PartNo=DXE-CGB-150
> then another length of coax that forms the rotor loop, goes up the mast
> then to the f12 balun (f12 B1) at the feed point of the D240. I have
> the same setup via another coax cable going to the C31XR which doesn't
> exhibit this strange problem
>
> I have two weep holes drilled in the bottom of each trap cover for
> moisture to escape.
>
> All connection points are weatherized using 3m rubber splicing tape
> which is then wrapped with Scotch Super 33. All coax, connectors etc
> are brand spanking new.
>
> The next step is to climb the tower and check the connections at the top
> of the tower, if that's not the problem it will be time to bring out the
> crane again and check the connections at the feed point.
>
> Before I get to far into this I'd like to know if any else has run into
> this symptom and what the final resolution was.
>
> Thanks
>
> Rich - N5ZC
>
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