[TowerTalk] Full 40 mts dipole on side of a tower

[Dave Sublette]

My mistake.  The coax in the choke is RG142, MIL-C-17 27478 from Harbour
Industries--- good stuff.

Dave

On Mon, Apr 2, 2018 at 11:07 AM, john at kk9a.com <john at kk9a.com> wrote:

> RG392 has an aluminum braid, could you have a back shield connection?
>
> John KK9A
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> Good morning Craig,
>
> You make several good points.  As I measured the dipole hanging away from
> the tower, there was 100 feet of RG8X used as a feedline.  It is known to
> be good and I check loss often.  It is my "utility" roll of cable, kept for
> purposes like this, antenna testing, etc...
>
> The SWR started at 1.1:1 at 7.0 Mhz and rose smoothly to 1.5:1 at 7.3Mhz.
> Obviously, the dipole needs to be shortened. But since I operate almost
> exclusively on CW and hardly ever above 7.2Mhz SSB, I decided to leave it
> there.  I didn't use any sort of balun for this test.  I have a balun on
> the tower, along with the the permanent feedline, a new piece of "buryflex"
> cable.  The balun is one I made.  It is actually a common mode choke, RG392
> wrapped six times around a Type 31 core, and then repeated on another core
> about six inches later.  This is all my best effort to replicate info I
> find on K9YC (I think) website and the K7 fellow's website, who sells the
> things.
>
> My analyzer is a Comet CAA-500, the original, not the newer one with LCD
> screen.
>
> I have also simulated the antenna using accurate diameters and section
> lengths using the Antenna Model Software.  I ran analysis at 5 feet, 25
> feet, 50 feet, 75 and 100 feet.   I then took the data at those heights as
> I was pulling the antenna up the trolly wire.  It behaved just about like
> the simulation said it would.  It was a great exercise for checking the
> accuracy of my model against the "real world".
>
> All in all, it has been a fun project.  I built the antenna out of scrap
> parts left from my old Telrex yagis.   Next step is to build a pair of
> Moxon 2 el 40m yagis from some more of the leftovers.  This dipole was
> mainly a "warmup" exercise to validate the modeling technique.  With this
> dipole in place and the two Moxons mounted at 145 and 75 feet above and
> below it, I will have a good setup to measure gain and F/R of the Moxon
> stack compared to the dipole.  This will be with only the 40M antennas on
> the tower.  Later, when I build and mount the next antennas, I can check to
> see if there is any degradation of the system.
>
> It is a really fun project and it keeps me off the street and out of the
> bars  :-)
>
> 73,
>
> Dave, K4TO
>
>