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9
Tuning information
The antenna is an advanced design that delivers excellent characteristics across the entire FM band.
ExterminatorII®
delivers performance that rivals a 2-bay multi stacked phased array. To achieve maximum results the antenna should
be mounted as high as possible, clear from all other obstructions. We have included a pack of U-Bolt brackets to
provide for easy mounting. If you are mounting the antenna on a mast/tower with other equipment the antenna
must be set at least 3 meter or one wave length from any other antenna.
For tuning use a meter designed for the intended frequency band. Preferably use antenna analyzer such as RigExpert
AA-170. If you have to use SWR meter, do not attempt to measure SWR at high power levels; resulting high SWR
could damage the transmitter and is also exposing you to unnecessarily high EM field. Do not touch any parts of the
antenna when reading SWR. Also move as far away from the antenna as possible during measurements. If you are
tuning the antenna on the ground you must ensure the antenna is at least 2 meters above ground level to minimize
impact of ground on the readout.
Primary tuning is done by setting the length of the main element equal to .82 wave of your operating frequency. This
is measured from the lower edge of the aluminum hub to the tip of the main element; the main element is made up
of three (3) tubular sections. The first element is the “main” section that secures the antenna components, the
second and third elements are adjustable and can be extended / retracted.
The correct length of the main section (elements 1, 2 & 3 combined) is calculated in inches by using the formula of
9212 divided by your frequency in MHz Example: 104.1MHz would be 9212 / 107.1 = 88.4 inches. Remember
measure from the lower part of the main aluminum hub, do not include the length below the hub with connector,
this is for mounting purposes only and is not actual accurate antenna’s tuning which can only be done with a SWR
analyzer or meter.
Frequency: Extend To:
88MHz =
2,66m (104.6 inches)
90MHz =
2,61m (102.3 inches)
92MHz =
2,55m (100.1 inches)
94MHz =
2,49m (98.0 inches)
96MHz =
2,44m (95.9 inches)
98MHz =
2,39m (94.0 inches)
100MHz =
2,34m (92.1 inches)
102MHz =
2,29m (90.3 inches)
104MHz =
2,25m (88.5 inches)
106MHz =
2,21m (86.9 inches)
108MHz =
2,16m (85.2 inches)
The next adjustment is measured by the length of gamma rod set into the lower portion of the captive tube (air-
capacitor). Further adjustment is determined by the location of the gamma rod and the bracket. Moving the bracket
up and down will change inductance; this sets the balance between the inductive and capacitive components that
make it possible to produce the correct resonance and a flat 1:0 SWR. When both the inductive reactance and the
capacitive reactance are equal at your frequency they will cancel each other out and present 50 Ohm resistive load to
your transmitter.
We have set the “shorting strap” (the part where the gamma rod is secured to the main element) to its optimum
position, under most conditions you should not need to re-position this part.
Chapter
4
