That's a good point. I'm pretty certain that the Delta 240 uses a
hairpin match (small coil across the feedpoint) so there would normally
be a low DC resistance at the shack end of the coax if all the
connections were solid.
73,
Dave AB7E
On 4/1/2012 10:28 AM, Danny Pease wrote:
> Sounds like an issue with the center conductor contracting when it is cold
> and expanding in length as it warms up. Have you tried checking with an ohm
> meter both when it is OK and when the SWR is high?
>
> NG9R
>
>
> Message: 5
> Date: Sun, 01 Apr 2012 10:01:08 -0500
> From: Richard Thorne<rmthorne@att.net>
> Subject: [TowerTalk] Stange SWR/AttenuationpProblems, goes away when
> the sun comes up
> To: Towertalk<towertalk@contesting.com>
> Message-ID:<4F786DB4.4060908@att.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> 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={DBD
> 52E00-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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>
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