The Antron 99 EXPOSED!
(By Tech 833)
Have you ever wondered what was inside the Antron 99 antenna?
A long time ago, I purchased a Solarcon Antron 99 antenna for my propagation beacon. The Antron 99 is
really a CB antenna, but with only slight returning, it works very well on the 10-meter band. In the Antron
advertising, it explains that it is a '1/2 wave over 1/4 wave variable mutual transductance tuned antenna'
with a dB gain of 9.9 dBi. No way I thought.... However, the price was low, so I bought it anyway. After
discovering that the Antron 99 performed worse than the 5/8 wave ground plane it replaced, I set out to
discover why. What follows are my findings after dissecting 2 separate Antron 99 antennas.
In this photo, you can see the insides of the Antron 99 laid alongside the shell it was once housed in for
size reference. In this photo, you see what is inside the base and how it fits inside the base section. Except
for the lower 2 feet of the Antron 99, all the rest of the antenna contains nothing more than a straight piece
of #16 bare copper wire!
Here, you can clearly see the small section of coaxial cable that connects to SO-239 connector in the
bottom of the mounting pipe and to the coils of the matching section. No 'magic' here at all. Just above the
coils is the capacitor coupling, which is made of a nylon spacer and brass tubing. The 'twin ring' match
merely changes the inductance of the outer tuning coil.
In this photo, you can look down inside the capacitor-coupling unit. This photo was taken from the radiator
end looking back toward the base assembly. To get an idea of how this works, imagine plates of a battery.
Current can flow between them, right? The only difference is that instead of battery acid or gel electrolyte,
the nylon spacer assembly is the electrolytic for in this case, 'plates' of the capacitor. The wire going down
the middle does NOT go all the way through (see the schematic at the bottom of the page). Notice the
HORRIBLE soldering job! Obviously, there was not enough heat applied to this solder joint. Also, by
adding this much series capacitive reactance, there must be a lot of series inductance to offset it. A very
lossy approach!
This photo gives you a good view of the coax type and also how the inner impedance matching coil fits
inside the outer tuning coil. Since the Antron 99 is nothing more than a standard end fed 1/2-wave dipole,
the base impedance is nearly 1,000 ohms. In order to get a 50-ohm feedpoint on a 1/2-wave element, the
antenna is shunt fed. The inner coil provides the 50-ohm point at the base of the radiator. The outer tuning
coils adjust the reactance over the selected bandwidth. Once the reactance is at or near zero, the SWR will
be very low.
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