[TowerTalk] Shunt Feed vs. Inv. L vs. Inv. V on 160-m

[Roger (K8RI) on TT]

On 12/3/2013 6:52 AM, john at kk9a.com wrote:
> #2 would be my last choice.

A thought:
I would think the slant fed tower would have a lower angle of radiation, 
but I've had very good luck with a quarter wave, half sloper fed 
directly with coax (shield to tower)at the top which is about 95 feet, 
but half slopers can be finicky.  I tried it, got lucky, and it worked 
first time.  Very narrow band and IIRC the impedance is about 25 ohms. 
I've used the Palstar AT5K tuner in the shack successfully with the 
legal limit and no RF in the shack. Although probably not the best 
arrangement it's convenient.

73

Roger (K8RI)

>
> John KK9A
>
> To:	towertalk at contesting.com, topband at contesting.com
> Subject:	 [TowerTalk] Shunt Feed vs. Inv. L vs. Inv. V on 160-m.
> From:	RLVZ at aol.com
> Date:	 Tue, 3 Dec 2013 00:30:26 -0500 (EST)
> List-post:	 <towertalk at contesting.com">mailto:towertalk at contesting.com>
> Hi Guys,
>
> Looking forward to getting back on the Top-Band for the next  couple of
> months and working some contests and some good DX.   I'd  appreciate your
> recommendations on the antenna options for my temporary FL  QTH this
> winter.  I
> don't own modeling software,  nor would I know how to use it if I did, so I'm
> hoping that some of  you will share real-world experiences.
>
> At my Florida QTH, I've got a 90' Universal self-supporting  Alumimum tower
> available, it has a 10' top-mounted Aluminum VHF antenna which I  believe
> is DC grounded, therefore a total tower height of 100'.   There are no Yagi's
> on the tower (no other top loading), but no steel guy  wires to interfer
> with the pattern as it's self-supporting.  Radials are  limited due to about
> 66' due to space  limitations. On the positive side, the tower is only 100'
> away from a salt water canal on it's East side and the canal runs North and
> South.  Therefore, the tower looks over saltwater to the  North-East-South.
>
>
> Last winter, I "Slant-Fed" fed this 90' tower as follows:  attached a #10
> copper wire to the tower at the 50 ohm point on the tower which  turned out
> to be 25' off the ground and 1/4th the way up the  tower.  The other end of
> the #10 wire runs out 30' away from the tower and  down to the ground level
> to a convenient location.  RG-8 coax feeds the bottom end of this #10 wire
> and a capacitor was  placed in series between the coax and the #10 slant feed
> wire in order to  achieve 50 ohms and J Zero.  (aprx. 250pf)  The coax braid
>   connects to an 8' ground rod and to a half dozen 66'  radials.  I also run
> a 2" copper strap from the tower base to the base  of the Slant-Fed wire.
> (the tower has a lightning ground system which  I believe makes it into a
> brackish salt water because 100 years ago  the  the property was a salt water
> swamp)
>
> Last year's performance of the slant-fed 90' tower was fair to  midland,
> but surely not excellent.  This year I  can repeat the same "Slant-Fed"
> system, or I can hang an Inverted V with apex at  the 90' level which isn't
> dependant on a good ground system, or I can put up an Inverted L with
> aprx. 85'
> vertical and the rest  horizontal and aiming NE towards Europe.  (If I do
> the
> Inverted L, I will be limited to the same marginal radial system of 6- 66'
> radials.
>
> Since my radial system is marginal, any predictions  or recommendations on
> which of the 3 antennas would work best for DX?   Again, the 3 options are:
>
> 1) Slant-Fed self-supporting 100' aluminum tower that has no  top loading.
> (a shunt-fed tower with 6- 66' radials).
>
> 2) Inverted Vee with apex at 90' and ends  up 20'.
>
> 3) Inverted L with apx. 85' vertical and the rest  horizontal.  with 6- 66'
> radials).
>
> Thanks in advance for your thoughts, 73, and hope to work you  this weekend!
>
> Dick- K9OM/4
>
>
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