Sunday, October 30, 2011

Lying Down on the Job

Many of you knew about our cooling system problem with TX6.  The old pump was overloading due to it spinning too quickly on our 60Hz power.  We received a new pump by way of a lot of help from ministry supporters.  We were able to swap the pumps and get the new unit working in one day.  We spent quite a bit of time lying down to get the job done.
The transmitter has been working well in short test broadcasts.  It even helped us find a problem with another transmitter.  All the while, it is keeping its cool.  It's a good thing because the new broadcast season starts tonight.  It will be broadcasting the Good News to China, India, and North Korea.  Listeners in India have already been very excited with the good signals coming their way. 

Monday, October 3, 2011

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.