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. 

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.

Wave of the Future

We have had an encouraging learning experience during our DRM test transmissions. The spectrum analyzer display shows the typical "Bart-head" waveform that a DRM broadcast creates. TX6 was able to acheive a "shoulder depth" of at least 32dB, which is quite good.

There are still bugs to be worked out with the data being sent from the content server to the modulator in the transmitter. These bugs are creating occasional breaks in the audio. However, the sound quality is amazing for a shortwave broadcast. We have received listener reports from Japan and Australia. The main beam of the 75KW signal was actually headed toward India.  You can go to www.youtube.com/watch?v=6e2Lnmx2LU4 to hear the signal that was received in Japan.

More Testing

A few more accomplishments at KTWR…
 

75% Power Test

With the Antenna connection completed, we are now able to test The Thomson Transmitter at higher power. On August 31 we were able to bring the Thomson transmitter to 218KW. The transmitter ran smoothly with very low reflected power.

Content Server Test

The Transmitters at KTWR Guam are two Harris SW100 Transmitters (100KW), one HCJB HC100 Transmitter (100KW) and now the two reconditioned Thomson TRE2326 transmitters (250KW).

We have had an ongoing project to upgrade the HC100 Transmitter to DRM (Digital Shortwave) for several years. One of the devices needed to broadcast digitally is a content server which formats audio into the correct form of digital audio.

We have not been able to work on the HC100 upgrade for a long time, due to the Thomson transmitter installation and other complications. We felt it would be a good idea to test the content server so…

We configured the content server to stream Digital content to the new Thomson transmitter because the Thomson is already DRM capable.

Here are the results.

Sept 2^nd 75KW DRM

We are very Happy to report the Content Server Works Very Well!!

Testing, Testing, Testing... and... RF ON!

3 August 2011 Thomson Transmitter status display indicating "Unknown State":

Considerable progress has been made in Connecting Power, Air and Water cooling systems. Most connections were completed just before Marc Moreau (Thomson Engineer) arrived for an Installation evaluation and inspection.

Marc arrived on August 3^rd with the Transmitter in a functional unknown state.

For the next week the project team worked 12 to 14 hour days testing, repairing electrical control components, fixing water cooling leaks, rebuilding computers, etc….

On Tuesday morning August 9^th a temporary antenna connection was made.... and....

We are pleased to report on 9 August 2011

we successfully accomplished an initial power up RF test. For about 10 minutes we aired a station ID test and music tone at 0500 UTC on 31M at 57KW.

9 August 2011 Thomson Transmitter status display indicating all systems "ON":

Thank you for your continued prayers as we move forward to reach the Late October goal for sustained broadcasts using this powerful communication tool!

RF Test Video

Raising The Balun - 2

A balun is a type of electrical transformer that joins a balanced line (one that has two conductors, with equal currents in opposite directions, such as a twisted pari cable) to an unbalanced line (one that has just one conductor and a ground such as a coaxial cable).

This balun weighs around 660 lbs. This really wasn't a big challenge for our riggers who quickly had the necessary equipment for hoisting up the units. The real challenge was the amount of space needed for the large balun unit. It had to be raised and turned from an area half the size of its length.

It was a bit time consuming, but it all went without a hitch, as this was all successfully connected together. The remaining part of this project is to now get the feed lines out through the wall and connected with the curtain antenna

(We did 'raise the roof' as we thanked the Lord for the successful and non-eventful raising of the balun.)

Raising The Balun

This is not like raising the roof (creating a loud noise), or raising Johnny (teaching children the disciplines of life).

This is about hoisting the VHF filter and the Balun to connect them as part of the RF output of the new transmitter. They are raised up to the roof however (suspended from).

The VHF filter unit weighs approximately 300 lbs. This was the first unit raised to connect to the transmitter RF output.