Topband: Guy line affecting SWR/match

[Joe Subich, W4TV]

On 2022-01-07 2:37 PM, Raymond Benny wrote:
> 1, I am using Dacron, non-conductive cord at three points to guy the 
> verticals. Top guy is about 10ft from the top. It seems that about
> the start of our winter rains, the SWR and all changed. The guy lines
> are attached directly to the vertical with a thimble, no insulators.
> Could the wet guy lines be creating a leak to ground?
Yes.  Spiderbeam originally used Dacron covered kevlar for their element
ends and the wet Dacron seriously de-tuned the elements.  They went to
PVDF (monofilament fishing line).  I would suggest that you not only
need insulators at the guy attachment points but probably need to make
sure the bottom portion of the guy wire is not resonant anywhere in
2.8 - 5 MHz.

> 2. Could the ground conductivity and therefore the matching have
> changed because of the rain?
Absolutely.  Anything less than a "broadcast quality" (120 half wave
radials) *can* show changes with changing moisture levels.  Broadcasters
see changes with moisture levels when their ground systems start to
deteriorate.

73,

    ... Joe, W4TV


On 2022-01-07 2:37 PM, Raymond Benny wrote:
> All,
> 
> I have a situation that I have not encountered before and do not understand
> the cause. I am building an 80m 4 square TX antenna system. I put up the 4
> - 65ft irrigation pipe verticals between Sept and November when the
> ground/earth was quite dry. I installed 48 - 67ft radials on each vertical.
> At the time I resonated the vertical to 3.640kHz. Using my AA55 Antenna
> Analyzer, X=0 and R was around 46 ohms.
> 
> Because I have not dug the trenches and laid conduit for the Comtex control
> cable, I am feeding just one of the verticals so that I can get on 80m.
> This has worked fine, SWR 1.2:1,  until we started having our winter cold
> and rain/snow weather. The SWR is now near 4:1, and if I remember, the
> vertical is resonant at above 3.8 kHZ, the R & X  have changed too, but I
> have not measured them recently.
> 
> I am at a loss as to what is causing this change There are 3 or 4
> thoughts/questions I have as to this situation:
> 
> 1, I am using Dacron, non-conductive cord at three points to guy the
> verticals. Top guy is about 10ft from the top. It seems that about the
> start of our winter rains, the SWR and all changed. The guy lines are
> attached directly to the vertical with a thimble, no insulators. Could the
> wet guy lines be creating a leak to ground? I am planning to install egg
> insulators at the guy points very soon, depending on the WX.
> 
> 2. Could the ground conductivity and therefore the matching have changed
> because of the rain? I am direct feeding the vertical with a K9YC 1:1:
> toroid balun at the base. The ground here is a mix of typical soil: dirt,
> small rocks and hard clay. When I installed the verticals, you could only
> dig about 4 - 6 inches without much effort - there is no moisture in the
> soil. With the rains, I can dig about a foot without much effort. The
> ground below about 2 - 3 ft has not seen moisture since it was laid
> down eons ago.
> 
> 3, All  radials for the 4 verticals are lying over each other. I did not
> trim or solder the radials together where they cross. The radial layout is
> the same as before our rains.
> 
> 4, I detached the coax at the base and placed a 1500 watt dummy load to it.
> There was no reflected power.
> 
> As a note, for almost 8 years I had the single 72ft irrigation pipe
> vertical with 4 - 30ft top hat loading wires for 160m. Also, I had a 65
> foot drop wire spaced just 16 inches from the main vertical for 80m. I used
> the same radial field, and had two separate coax and matching inductors at
> the base. I did have to ground the main vertical (160m) in order for the
> 80m section to work properly.  All worked well and I did not see the effect
> as mentioned above during those 8 years.
> 
> So I'm stuck for an explanation and a remedy for my situation.
> 
> Any thoughts, comments or suggestions?
> 
> Ray,
> N6VR/W7YA
> 
> PS, Please excuse me for posting this on the Top Band reflector, but I
> think there is more knowledge and experience on this site than any other.
> 
> Near Prescott, AZ
> Nice rural, quiet location,
> On 5 acres at 4800 ft elevation,
> Winter low temps can vary from 15 to 35 degrees, with light rain and snow.