[ARDF] 2M Turnstiles

[Kenneth E. Harker]

     W5JEN and I have built our first two meter turnstile antenna based
on the WB6DRV contruction article:

     http://www.west.net/~jay/turnstile.html

     We modified the design slightly.  Instead of "4 ea. 8-32 x 3/4" 
round-head machine screws" we used 4 ea. 8-32 x 1" round-head machine 
screws, and instead of elements made from hex spacers and welding rod, 
we are using aluminum arrow shafts.  The arrow shafts have 8-32 threading 
inside (used to screw on an arrowhead) and are easy to cut to length with 
a Dremel tool.  You need to use 1" long machine screws instead of 3/4" 
machine screws because of how deep inside the arrow shafts the 8-32 
threading is located.

     Having built one of these, we've had a little trouble achieving a flat 
SWR.  Cutting the arrow shafts to various lengths between 19" and 17" results 
in a SWR curve that dips both below and above 145 MHz.  i.e. at 17.5" 
lengths, there may be a nice wide dip in SWR that goes as low as 1.1:1 from
137 MHz or so to 142 MHz, climbs up to 1.5:1 or 1.6:1 by 145 MHz, and dips 
again to 1.2:1 around 150 MHz.  Every length we tried seems to have this 
double dip, with the local maxima between the two dips topping out at 1.6:1 
or maybe 1.7:1, and usually around 145 or 146 MHz.  So, 1.5:1 isn't too 
terrible, but I find it odd that the SWR curves (a) don't seem to move much 
up or down in frequency, and (b) show a double dip.  I have not checked to
see exactly how omni-directional it is yet.

    One thing I wasn't sure about when we built this was how long, exactly,
the phasing section ought to be when you solder the solder lugs onto it.
i.e. should the 16" length be from the center of solder lug to the center of
solder lug?  Or from the tip of the solder lug to the tip of the solder lug?
Or is it really not that precise to matter?


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Kenneth E. Harker      "Vox Clamantis in Deserto"      kharker at cs.utexas.edu
University of Texas at Austin                   Amateur Radio Callsign: WM5R
Department of the Computer Sciences          Central Texas DX & Contest Club
Taylor Hall TAY 2.124                         Maintainer of Linux on Laptops
Austin, TX 78712-1188 USA            http://www.cs.utexas.edu/users/kharker/
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