Here are some observations I've noticed about bazooka type antennas.
It's a 1/2 wave length antenna and will behave/radiate as any 1/2 wave length antenna will. It will be
have the same radiation pattern and be affected by all the things any such antenna is affected by,
height above ground, whats around it etc. The biggest difference is in how a bazooka antenna is fed.
It's fed through a tuned circuit, a lot like a 'beta' or 'delta' match. That feeding method is why it has
such a 'wide' usable SWR range.
What type of coax cable used in the construction can make a huge difference in performance. Coax with
a 'foam' type insulation will not handle the higher voltages present as well as a cable that uses a 'solid'
type of insulation. So, RG-8X isn't a great type of cable to use for a bazooka antenna. (A voltage increase
is always a product of impedance transformations.) The old RG-8 type cable with solid inner insulation
tends to work better.
The old 'classic' bazooka with the open wire feed line type 'ends' uses those larger 'conductors' because of
end-effect, high voltage at the ends of a 1/2 wave antenna. Makes for less arcing, corona discharge.
Considering the intent of the original bazooka antenna, radar, which involves high power 'pulses', corona
discharge was a real problem. With typical amateur use those large conductor 'ends' aren't really needed.
You can still use them, won't harm a thing if you do.
The type of coax used in it's construction will also determine the different lengths of various parts of a
bazooka antenna. The overall length will stay pretty much a 1/2 wave length, but the lengths of those
center sections, the tuned circuits, will be affected by the velocity factor of the coax cable used. Those
center section lengths (electrical 1/4 wave lengths) are affected by the velocity factor of the cable, making
them 'shorter' than the full length of 1/2 of that antenna. That's why they are shorted toward the ends of
the antenna instead of just continuing to the ends, 'tunes' those center sections, right?
So why don't the 'numbers' work out exactly? Because there are a lot of variations in coax cable, none of
it is ever exactly the same on the same spool, much less the same manufacturing 'batch'. See how that
affects things?
Performance or efficiency is determined by what you are measuring with. A bazooka antenna is not very
efficient away from it's design or center frequency. A typical SWR meter is a terrible means of measuring
performance or efficiency. At best, an SWR meter can only indicate how well impedance matching is done
which has very little to do with how well an antenna 'works', how it performs. A dummy load is a very good
example of that, great SWR, lousy antenna. If your main criteria is SWR then a bazooka antenna is a very
nice antenna to use. If it serves your purpose well, then use one! There still ain't no such thing as a free
lunch, but if the price isn't too steep, why not?
- Paul