I was not aware that 3:1 was the lowest SWR., that is horrible, One other
thing you can do while it is mounted is feed it with 1/2wl of coax and look
at the impedance..
John KK9A
Sent via the Samsung Galaxy 7 edge, an AT&T 4G LTE smartphone.
On Mon, Apr 2, 2018 at 10:18 AM, Dave Sublette <k4to.dave@gmail.com> wrote:
> John -- sorry if I wasn't clear on my answer. I measured the SWR with the
> test coax, no balun, through 100 feet of RG8X, known to be good. It showed
> the lowest SWR at 7200, 3.0:1. It rose to 5:1 at the band edges. All
> measurements were made with the coax hanging at a 90 degree angle.
>
> The SWR curves will show a flatter shape, I believe, because the dipole is
> made with 1.625 inch diameter tubing for the first 24 feet either side of
> center, then 1.5 inch for another 6 feet, then swaged to 7/8" for the
> tips. It is made from old Telrex elements, but beefed up in the middle,
> because the first time I put it up, it broke in the middle in a 35 mph
> wind. It was before I got my stress analysis software. I expected it to
> break. I put it up to see where it would break so I would know where to
> beef it up. Backwoods engineering at its finest! :-)
>
> At this point, it is not a question of what frequency it shows lowest SWR,
> it is a matter of the SWR being unacceptable at the frequency of lowest
> SWR. Read my last post (this morning). I think I have a plan that might
> work. I will let everyone know when I have results to report.
>
> 73,
>
> Dave, K4TO
>
>
>
> On Mon, Apr 2, 2018 at 9:47 AM, john@kk9a.com <john@kk9a.com> wrote:
>
>> Good Point. I also thought that the initial SWR was good for a dipole but
>> perhaps it was not high or has a hairpin match. I asked where the new
>> resonant point is and did not get an answer. If it just moved I would
>> readjust the tips. I also wonder if the test coax and balun are the same
>> and in the same configuration (running 90 degrees from the center of the
>> element) as the permanent.
>>
>> BTW his initial post is here:
>> http://lists.contesting.com/pipermail/towertalk/2018-March/160150.html
>>
>> John KK9A
>>
>> Sent via the Samsung Galaxy 7 edge, an AT&T 4G LTE smartphone.
>>
>> AC0DS Wrote:
>>
>> Dave …
>>
>> I’ve been following this mystery since your first post. Lots of very
>> experienced people contributing (including yourself), so I’m sure the
>> solution will surface shortly.
>>
>> One thing that I just now recalled. I no longer have your initial post
>> handy, but remember that the initial test with the dipole hung up in free
>> space away from the tower was very good. In fact, so good that it seemed
>> suspicious. I think the SWR was something like 1.1 over the entire 40
>> meter band?
>>
>> Don’t know what height the dipole was, but even a perfect dipole won’t be
>> that close to 50 ohms at most heights. And, would expect to see some
>> variation over the band.
>>
>> Questions:
>>
>> How long is the coax and what type?
>>
>> You said you had a balun at the feed point. I assume it is a choke with
>> the coax wound around ferrite?
>>
>> How were you measuring the SWR?
>>
>>
>> One possibility is that you perhaps had some unintentional losses (or
>> measurement error) in your first test that went away when you mounted the
>> dipole to the tower?
>>
>>
>> 73 Craig AC0DS
>> _______________________________________________
>>
>>
>>
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>>
>
>
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