Good morning, Dick.
Don't know of anyone who makes a full size 80 as a standard product. We have
been asked occasionally for full size elements, which are certainly
possible.
Making a high-Q shortened 80 does require some TLC. If it doesn't, then
perhaps the antenna is not as high Q as one would like to believe! The
two choices are linear loading or coil loading. LB Cebik has covered
these types of techniques in some detail. The linear loading is the most
efficient, although it does require tuning the individual elements, as
the Q is quite high. Coil loading still requires at least checking the
frequency of each element, as there are variables in any technique. Our
longer 83 foot elements have a wider operational bandwidth than the 68'
ones, so are easier to set up.
We have also provided some extended elements, up to 89' using the standard
83' ones, plus another section in the trunk portion of each side.
The longest stock element we make is the 160 rotatable, which is 102'. It
can be utilized for 80 mtrs.
One of the issues with a full size is that the operational bandwidth still
does not cover phone and CW. This might be most Yagis utilize shortened
elements - besides the rotation system required.
The 80 I use has been reconfigured to a 2 element. I need more mast space to
do something else, so the driver had to be removed from the mast (was using
the 3el Zagi configuration). The pattern on the 2element is excellent, being
18-20dB F/S and F/B across more than 40 kHz. This is at a low height of 74'.
My location has a pronounced immediate rise to the long path, about 21'
within the first 200' in that direction, increasing to 40' within the first
350'. It then levels off for a couple hundred feet and then rapidly climbs
to more than 150'. To the east, it slopes about 10', then is level.
We do have a structural design for a full size element and have one customer
contemplating whether or not he can take the load on his tower.
Other than full size, using the 160 element at 102' might be a good choice,
perhaps even extending it a little farther (as long at the strength is
reatined). I would suggest using a non-conductive truss on any of the
elements, regardless of the length.
Please let us know how we might assist you. We have also made booms as large
at 6.5" at the center, so large antennas are familiar here!
Have a good day and 73,
Tom, N6BT
Force 12 Antennas and Systems
(Home Page http://www.QTH.com/force12 )
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