Antenna Question

We received a question about how the antenna used in our recent DRM tests affected the signal.  Now we get to tell you about an important part of our station that seems to be the most unknown to most of our readers.
The antennas at KTWR are all curtain antennas made of dipole arrays.  The one we used in the test is nearly identical to the one shown at the right.  It is configured as a 4x4x1.0.  This means it has 4 columns of 4 dipoles each with the bottom dipole being one wavelength above the ground.  There is a reflecter screen hanging behind the dipoles to force the signal to have one main beam instead of two.  The gain of this antenna can be as high as 22dB, depending on frequency and slew angle.  That makes the 75KW signal coming from the transmitter seem like 11MW heading to desired coverage area.

The direction of the main lobe of the broadcast signal is controlled by the slew box like the one shown to the left.  In the case of the antenna used for the DRM tests, the azimuth can vary from 290 to 345 degrees.  We used 290 degrees for the tests beamed toward India.  Some of the signal went to other places outside the main coverage area.  That is why people in Japan, Australia, and Brazil were able to hear the test broadcasts.
One problem with the tests was that signal propagation conditions in the ionosphere did not allow the signals to be received in India, as far as we can determine.  Had we performed these tests at night, the signal would probably have been very strong there.  A great deal of planning goes into the frequency choice and the timing of our broadcasts, so that they will be reliable for the entire broadcast season.