There are several ways to make a dipole cover all of 75/80 meters, and
also many ways that don't work.
A double Bazooka doesn't cut it. It only provides about 14% increase in
bandwidth at the expense of extra loss at the band ends. Even the
crossed double bazooka that provides about 55% increase in bandwidth at
the expense of even more loss, doesn't do it.
A cage dipole doesn't do it either unless you make the cage an extremely
large diameter.
A folded dipole will provide a little more bandwidth but it won't cover
the whole band either.
A fan dipole with one dipole cut for CW and one cut for the phone end
will work if you place the dipoles at right angles to each other.
This open-sleeve version of a dipole will cover all of 75/80 with less
than 2 to 1 SWR and have good efficiency.
http://rudys.typepad.com/ant/files/antenna_broadband_dipole.pdf
Be careful if you try to analyze this antenna with NEC. It is possible
but extremely tricky to analyze.
The method of applying a resonant LC network at the feedpoint of a
dipole, as shown in Chapter 9 of the ARRL Antenna Book will work,
however the version with the whole LC network connected directly across
the antenna will be limited to low power unless you use some honker size
caps to handle the current. The method used in the "DXers Delight"
(same chapter) can be used at high power. It provides a step-up
impedance for the caps so they don't have so much current. Neither of
these work well at high power using a toroid for the coil because of the
huge flux values. This technique produces three resonant points in the
75/80 meter band although resulting in an increase in feedpoint
impedance which then has to be matched. It is possible to implement all
the whole network and the matching with a single tapped coil.
There are many other ways to do this that also work with good
efficiency. Some of them are shown in Chapter 9 of the ARRL Antenna
Book. Beware of networks using coax in the matching network. Many of
those (but not all) are very inefficient.
Jerry, K4SAV
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