Switches Getting Busy

For the past several months, we have been only operating one antenna switch during the normal broadcast shifts. With the new broadcast season that starts March 29th, we will need to use more switches. This necessitated the completion of the control software needed to make the whole matrix work. While there are some tweaks to be done, we are basically at that point

The user interface is able show the operator which transmitter is connected to which antenna. The operator can also see if there is a bad switch. This system gives options for working around bad switches, which is quite unique for an antenna switch matrix. The same automation system that controls the transmitters and antenna also controls the switch matrix. This simplifies automation changes.

The antenna switch matrix will help us save money starting next season (beginning March 29th). It allows us to use our transmitters more efficiently in order to reduce power consumption. Being able to put any transmitter on any antenna adds quite a bit of flexibility.

All Transmitters Connected

 

KTWR now has all three of its transmitters and four of its antennas connected to the antenna switch matrix.  This is a major step toward being ready for additional broadcasts that we will be doing next season.  We now have the ability to move as many 100KW broadcasts as possible to our HC100 transmitter.  The bigger transmitters can now send higher power broadcasts to any of the coverage areas served by KTWR.

We still need to connect our other antennas, ANT3 and ANT5.  Those connections require relatively little effort compared to what has already been accomplished.  Another task that must be done to complete the project is to integrate the control software.  We are seeing good progress in that area.

 

Putting the New Guy to Work

KTWR's staff has gotten some fresh new blood to help out with the work at the station. Andrew has come out for a one-year term to put his missions heart and mechanical engineering training to good use.

The main thing we have been working on lately has been the RF switch matrix. We currently have two transmitters and three antennas connected to the matrix. We plan to get the remaining transmitter and another antenna connected to it on Friday. The remaining two antenna connections should be relatively easy to do once Friday's work is done. To get ready for the big job on Friday, we have been doing as much as we can to prepare for that day.  In this photo, Andrew is helping with the task of dropping the ANT5 feedlines to get them out of the way.

Please pray for us as we get the final physical connections done over the next few weeks. We also ask that you pray for the matrix control software integration and testing that is underway.

Dodged a Bullet

With the eye of Typhoon Vongfong passing north of Guam by ~40 miles, many people on the island felt that they had dodged a bullet. Top winds ranged from 40mph in the area around KTWR to 70mph at the northern end of Guam. Had the storm hit us directly, we would probably have lost our commercial power and water supplies.

Vongfong is now a super typhoon headed for southern Japan. Please pray for the people in its path.

KTWR could generate power with any of its three generators, but there was no back-up water supply. Since it is too muddy to work in the antenna field, we took the opportunity to install a 500gal water system. Now that it is functional, it is much easier for us to operate during the frequent water outages that occur during rainy season.

Making Power

Installation of KTWR's 30KW solar power system has been completed. It turned out to be a tough thing to do during rainy season. It is also not so easy to get full power output during the monsoon that we had just experienced. However, this photo shows the inverter pumping over 22KW into the power lines at the station. That is ~3 times the power that we consume at home when a water heater and two air conditioners are running.

We are already in the planning stages of expanding this system with an additional 37.5-67.5KW system. That would be plenty of power to make our power meter "spin backwards" during the day. This will cause KTWR to accumulate credits that can be used to reduce the power costs of our nightly broadcasts. Reduced costs will expand our ministry opportunities.

Matrix Now in Use

 

We had a very busy day today (September 19th). This was the day we had to move connections for two antennas  and one transmitter to the antenna switch matrix. We were a bit concerned when the day started off with thunderstorms, but the weather turned out to be good for most of the day.

Once we cut the antenna feedlines apart, we were committed to getting the job done. As can be seen from the photos, most of our staff worked on this day-long task. Antennas 2A and 2B are connected at one corner of the matrix.  TX7 is connected to the opposite corner.

 
 

TX7 tuned to the new connection very well. It should work better than it did with the temporary switch connections in our old dump truck.

When it Pays to Cut Corners

The antenna switch matrix was tested for its ability to maintain the proper impedance with various transmitter-to-antenna connection combinations. The transmitters ideally want to see 300 Ohms with no reactance as the RF power travels from the transmitter to the antenna. That perfect situation almost never happens, so the transmitter must tune to make up for mismatches. Our matrix is unique in that there are cases in which it allows multiple switch paths between particular transmitters and antennas. Each path must appear the same to the transmitter to avoid extra time spent in tuning.


Maintaining the proper distance between conductors helped the matrix exhibit the 300 Ohm resistive load. That was not particularly difficult. Keeping the reactive load as close to 0 as possible was more challenging. Quite a bit of work went into using 45-degree fittings to avoid 90-degree corners. Sharp corners add inductance. Too much inductance can cause problems in transmitter tuning.


The good news is that the measurements were nearly perfect for all switch combinations at all frequencies in the 6-18MHz range. Avoiding the sharp corners in the pipes really paid off. The transmitters will essentially not notice when the matrix is connected between the antennas and the transmitters.

We are currently working on verifying that the automated switch control will work. Once this is proven to work, TX7 and ANT2A/B will be connected to the matrix. Other transmitters and antennas will follow during the next several weeks.