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Friday, September 26, 2014

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.

Friday, September 19, 2014

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.

Friday, September 12, 2014

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.

Saturday, September 6, 2014

Little House on the Prairie

After a lot of hard work and dry weather, we managed to construct a little block building to house the antenna switch controller and the power panel.  The forklift definitely made the bucket brigade for pouring the roof concrete much easier.

While the concrete was setting, a trench was dug between the transmitter building and this block house.  Conduit and power wiring has been installed and the trench has been refilled.  Conduit and its associated power and control wiring has also been installed between the block house and the ten antenna switches.

The switch controller and the power panel have been mounted inside the block house, but are not yet fully connected to other equipment.  We should be able to do some testing of the switches next week, unless something unexpected comes up.  (Something unexpected nearly always changes our plans.)