[TowerTalk] Feeding a "Super Sloper"

[N4ZR]

(You can skip to the next-to-last paragraph if you wish; it's where the 
question comes in)

I'm experimenting with a 40M antenna built by W1LWH, based on W7WKB's 
article in December 1995 QST.  It involves two parallel 3x1/2 wave 
sloper elements, with the parasitic element offset lengthwise by 1/4 
wave toward the lower end, and spaced 0.02 wavelength from the driven 
sloper.

The author describes the feedpoint resistance as being in the range 
150-165 ohms, from 7.0 to 7.25 MHz, with reactance over that range 
basically 0-10 ohms.  I am feeding the antenna with what is intend to be 
1/2 wave of 450-ohm open wire line, with a velocity factor of about 
0.91, the idea being to replicate the feedpoint impedance at the end of 
the open-wire line.

As can happen in the real world, I neglected to measure the required 
length of the feedline  before putting the antenna up.  Rather than take 
it down, I cut the feedline (hopefully) more than long enough, thinking 
that I could trim the length before connecting a 4:1 balun.  Using my 
trusty MFJ-259B, through the balun, I measure r 40+j 24 at 7050.  In the 
real world, both my transceiver and my amp load it fine, so I suspect I 
don't really need to adjust the open wire line. However...

Finally, the question. Assuming that the feedpoint reactance of the 
sloper is close to zero, does anything about the measured impedance 
above (40 +j24) tell me whether the open wire line is too long or too short?

Have pity, guys - I was a history major in college.

-- 

73, Pete N4ZR
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