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Question on 1/4 wavelength transformer



 I'm looking at ways to feed a pair of crossed 70cm yagis so I can switch
the
 polarization for satellite work.  I've researched the Satellite Handbook
and
 ARRL Antenna Book and these questions arise from those readings.

 First, the antenna in question consists of a pair of 10 element yagis on
one
boom, with a 1 inch offset between the vertical and horizontal elements (NOT
a 90 degree spacing!).  The yagi driven elements are gamma matched and I'll
assume for now that they're supposed to be adjusted for a 50 ohm match.
While this antenna is believed to be Cushcraft, there's no documentation
available, although I have the manual for the Cushcraft A144-20T Twist,
which is identical in construction, but for 2 meters instead of 70cm.

 Now the questions:

 1. Forgetting the requirement for switchable circular polarization for the
moment, the Cushcraft literature shows, for "Axial Radiation", connecting
the 50 ohm feedline to a "Tee" and then running an unknown length of RG-59U
to the two gamma matches.  I assume that this length is an odd multiple of
1/4
wavelength at the operating frequency (won't odd multiples of 1/4
wavelength perform the same transformation as 1/4 wave?).  I don't
understand why matching section is 72 ohm line.   With a single antenna and
a feedpoint impedance of around 110 ohms, the 72 ohms would make sense to
transform the impedance to that of the 50 ohm feedline.  Perhaps the gamma
matches on these driven elements are actually adjusted for a 110 ohm match
and then it would make sense to me.  What do you think?  Does the fact that
the two antennas are being connected to a single feedline factor into the
impedance chosen for the matching sections?

 2. On page 10-10 of the Satellite handbook, Figure 10.11:  The figure shows
feed systems for crossed yagis and again the 72 ohm transformation section
appears, so, same question as above.  I want to use system (A) in that
diagram, since the (B) and (C) apply to crossed yagis with a 90 degree
offset.  In (A), I'm puzzled by why the 1/4 wave delay line is 95 ohms.  By
the way, in these three systems the yagis are assumed to be 50 ohms
resistive.

 If you can shed any light on either or both of these situations, I'd be
very
grateful.

 K8AC
Floyd Sense - Angier, NC



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