[TowerTalk] Strange SWR/Attenuation Problems

[Jon]

I've seen this topic crop up on the repeater-builder group and it is
typically due to the center conductor
of the long run of coax contracting at night and then lengthening during
the heat of the day as was mentioned by
Danny.  In your other similar run are you using the same type of coax and
connectors?

73.
Jon
KD5SFA


On Sun, Apr 1, 2012 at 1:13 PM, David Gilbert <xdavid at cis-broadband.com>wrote:

>
> 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 at att.net>
> > Subject: [TowerTalk] Stange SWR/AttenuationpProblems, goes away when
> >       the sun comes up
> > To: Towertalk<towertalk at contesting.com>
> > Message-ID:<4F786DB4.4060908 at 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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