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Quad Helix



Good afternoon to all,

I finally completed the quad helix project here about two weeks ago.  The
results have been gratifying.  I have been able to hear the downlink at
all ranges as long as the squint angle is less than 30 degrees.  The
QSO's i used to struggle with are now easy if not armchair copy.  I still
can't hear the transponder noise floor but I can hear a db or two of sun
noise.

The array consists of 4 thirty turn antennas on 1 inch PVC.  They are
connected via a home made 4 way splitter with 15 inch pieces of 9913 flex
type cable.  It would appear that this antenna along with the
installation of a DEM preamp is about 6 db better than my original 21
turn antenna into a 3733 converter with input stub clipped and murata
filter installed.  The measurements I have made indicate the following
increases:

30 turn antenna compared to 201 turn antenna		-	Plus .5 to .75 db
4 30 turn antennas compared to single 30 turn antenna 	-	Plus 4.5 db 
Addition of DEM preamp directly to splitter		-	Plus 1 db

I could have possibly squeezed out another db if I had used a cup on all
antennas.  On one antenna that I built which used a cup (actually a brass
bucket) showed about 2 db more gain than the 21 turn antenna but when I
went back to get more buckets they were all gone!  I decided to put the
antennas up with out the cup.  If I were starting over I would build 20
turn antennas in a cup (providing I could find a suitable cup).  I built
a number of antennas in a number of forms with several types of elements
but I couldn't get anything to work better than the 1 inch PVC.  In the
final antennas I used 1/8 inch aluminum ground wire (from Radio Shack)
for the elements.  When I started out in January I was using the grounded
feed designed by W0OQC but in the end I used a simple conventional type
feed made from a straight piece of 1.25 inch by .25 inch brass.  When
spaced 1/8 inch from the reflector the 2.4 ghz bridge indicates a near
perfect match.

The 17 type "N" connectors makes this an expensive way to get 6 db gain
but the experience was gratifying.  It's also gratifying to be able to
hear the signals on the bird.  I believe it is perfectly adequate for low
squint angle operations.

73's de Jess - W4MVB


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