Another All Band Vertical

Some time ago I realized that I could make a multiband vertical by simply taking half of my 80/40 meter trap dipole and turning it on end.

There is another way to do this by using a tapped, switched, loading coil at the base.

I recently saw a design that covered four bands with a 27 foot vertical radiator. A quarter wavelength on 40 meters is 33 feet. That 27 feet is a mite short for a quarter wavelength on 40 but add a little inductance and you have a quarter wave resonant radiator for 40 meters

With considerably more inductance you can force the thing to be an electrical quarter wavelength on 80 meters.

Other bands can be covered by forcing them to be resonant as 3/4 wavelength and 1/2 wavelength radiators on the bands of interest.

The main difference in utility between the trap vertical and this is the need to change taps on the coil for this design. A trap vertical will cover multiple bands without need for tap changes.

There is also a large functional difference between the two designs. In a trap vertical, each trap acts as an automatic switch disconnecting sections of the antenna that are not needed at the higher frequencies. For instance, a trap vertical will disconnect all but about an 8 foot section to obtain resonance on 10 meters. When you consider that the live section remaining might only be a few feet above ground, you may well fear some problems getting the smaller antenna to radiate effectively.

By using 3/4 wavelength and 1/2 wavelength sections you use more of the the full length of the vertical. It has always been assumed if not written that an effective antenna presents as much metal as high as possible into the sky.

The disadvantage of having to change taps can be solved by providing a remote switch to do the job.

One additional factor to consider is bandwidth.  The higher frequency bands usually have plenty of bandwidth, but the lower frequency bands ten to suffer with bandwidths as low as 100khz on 40 and 50khz on 80.

This situation can be improved by not trying to cover all bands with traps.  A dual band, 80/40 meter antenna using a pair of traps will have a bandwidth more than twice what was quoted above.  Better but still not capable of covering the entire band on 80 meters.

Depending on your operating habits, there may not be any need to improve bandwidth.  Just center what bandwidth you have on the frequency that interests you.

Explore posts in the same categories: HamRadio

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