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Author Topic: Verticals, UnUns and High Power  (Read 1989 times)

Posts: 60

« on: November 17, 2013, 06:20:41 AM »

In my last post, I mentioned problems with 15 meters using an UnUn for 43' verticals from DX Engineering (5KW) at power levels over 300 watts. The SWR climbed from 1.0:1 to 1.2:1 and would return to 1.0:1 after not transmitting for a few minutes with the tuner. I added a 15 meter 1/4 wave vertical inside the S9V 43 fiberglass tube and I change the connection to the SO239 connector at the base between the UnUn - 43 and the 15 meter 1/4 wave. Excellent performance and stable SWR for 40, 20 and 15. I only use the 43 for 40 and 20 now. The radials are 6 inches below the cutting blades of the Miami's finest landscapers, which is just far enough to keep these diligent destroyers of grass from mowing the radials, about 2 inches in the ground.  I have a Palstar AT2K and I am not interested in using an auto tuner with the Alpha 86.  I'm not far from the ocean and we have a lot of corrosion here. Not a good place for an outdoor tuner.

Posts: 3131

« Reply #1 on: November 17, 2013, 06:08:52 PM »

SWR rising from 1.0 to 1.2? 

I guess I missed that on your first post.  That's not a "problem". That's barely outside of meter readability for most SWR meters.   Most hams would kill for SWR's like that.

If that is all that's the extent of the matter, I wouldn't give it a second thought.  As long as you don't see larger excursions or note considerable warming of the Unun, or coax; nor any arcing, move on!

As always, when troubleshooting, simplify the problem.  Try removing the Unun from the line and see how things perform.

73,  bill

Posts: 2226

« Reply #2 on: November 18, 2013, 06:42:32 PM »

Ok sounds good. I have worked with wire verticals even to the same end where I used three critical lengths specifically to divide 80m- 10m utility where the verticals would be utilized between the 1/4 wave to 5/8 wave   and integrated tuned 1/4 wave elevated radials sets of two per band.
2-80 2-40 2-20 2-17 2-15 2-12 2-10m.
It worked very well.

All the radials were sloped downwards and anchored using non conductive stakes for isolation.

The long wire vertical was 65ft in length.
The intermediate vertical   33ft
The short vertical 25ft.

The switched L auto tuner was used when I wanted to tune the 25ft vertical on 20m and up.
The range of choice in my opinion is from the 1/4 wave to 5/8 wave for best low TOA etc.
When I used the vertical as a quarter wave such as on 40m the tuner was bypassed.

The unun that you are using is a good one and core heat is not an issue as you have verified sounds good enjoy as I have.

The system that you are using will be fine and the log book will demonstrate that over time!

As a added comment use a wander lead outside to a earthing rod to bypass the antenna to ground and or lightning arrestor for the center conductor also outside located with the rod and wander lead.
Use the wander lead to divert the antenna to the earthing rod when expecting those thunderstorms down there.

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