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The KJ4IIF Multiband "FAN" Dipole for 160, 80
and 40 Meters(Optional 20 Meter band addition
also)(Using Techniques and modified
formulas from SRI research with Fan
Dipoles)
I did not model
this with any antenna modeling software. I did it the old fashioned way.
With formula's, cut and prune, a cooler full of cold drinks and some
friends to help pull that heavy antenna up in the air. Included at the bottom
of this article is a frequency vs, "X" and "R" plus swr
results chart for all amateur bands, 2 meters through 160
meters. There is also a link to a harmonic relationship for all bands
courtesy of and compilied by N5JNX.All measurements
are taken with an MFJ 259B analyzer. Apex of the multi
band dipole is at 58 feet, Ends of the 160 leg are at 20 feet above
ground. The multi
dipole has a 1:1 current Balun at the feed
point.
In the photo
above, the legs of the multi band dipole are spaced 6 inches apart
vertically, four inches apart horizontally at the feed point. I used
14 inches of non conductive Lucite
six inches wide as shown.I spaced the dipole legs with 1/2 inch PVC, Six inches from the fed point where the legs come off the Lucite. I drilled 1/4 inch holes through the pvc and threaded the wire through the holes. This keeps the wires separated at the feed point. See
photo above.The top dipole is cut for 160 with a center frequency of 1.9 mhz formula
is 468/1.9 X .96 works out to roughly 118 feet per leg.The center dipole is cut for 80 meters with a center frequency of 3.85 mhz. The formula is 468/7.18 X 1.04 works out to roughly 63 feet per leg. The bottom dipole
of the multi band dipole is cut for 40 meters with a center frequency
of 7.18 mhz.The formula is 468/7.18 X
1.04 works out to roughly 33' 10" per leg. Note: Always arrange the dipoles with the
lowest frequency band first, (on top), then the next higher frequency band
under it and so on. You should end up with them in this order from the
top:
So
there you have it....Four bands, one feed line, no antenna coupler
required, and 15 meters as a bonus on the harmonics. And with the optional
20 meter band addition, you can have 5 bands all working well...see 20 meter additiion information
below.Remember that this fan dipole was designed for the 160, 80 and 40 meter bands. In the chart below you will notice a very low swr on each of these bands with red numbers! It also appears that many other bands may be used with a tuner.
Click here for the Harmonic relationship
chart for this antenna for all bands by
N5JNX.Adding the 20 Meter addition as an option! Just as an
experiment, I added a separate 20 meter addition to the fan
dipole.I now have,
15/20/40/80/160 meters on one antenna
20 meters worked exactly as the
others.Formula used : 468/freq X
1.04End Result Band Width for the 20 meter
addition
Spacing at feed point was
identical to the 3 band version, six inches
apart.Further experimentation.
Maybe later, I will try
to add 10 meters but the FAN configuration is starting to get out of whack
with that many wire elements on one antenna. I may have to space the 10
meter feed point 12 inches from the 20 meter feed point to try and make it
at least a 45 degree dipole.Side by side
comparisions on recieve show a 10 to 12 db less than the Mosley TA33 at 75
feet, about two S units less than the beam, so it is as it should
be.So there you have it....Four bands, (5 if you add 20), one
feed line, no antenna coupler required, and 15 meters as a bonus on
the harmonics with the designed bands having very low
swr!Try it! 73 -
KJ4IIF
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