Sunday, July 12, 2009

1296 Antenna Testing

I just finished doing some tests on my 3 1296 yagi's. The first was a WA5VJB wood boom yagi, the second, was designed on VK5DJ's calculator, the third was a loop yagi. Knowing that the loop yagi works reasonably well, it was the antenna to beat.

This test was done in a rather unscientific manner. The signal source was a 48 MHz oscillator using ambient radiation from its open enclosure, located about 50 feet away from the antenna under test. The 27th harmonic was weak but quite noticable in the receiver. I did not use any metering to determine gain from one antenna to another, but just compared them all "by ear". I have no way of determining the return loss of the antennas under test. The "antenna range" was not ideal either, located between 2 metal structures about 50 feet apart. I was able to notice decent directivity and antenna gain between the antennas I tested. I figure that the directivity would give some indication of gain. Anyway, here are the results of this test:

The WA5VJB 10 element yagi compared favorably to the 19 element looper. Directivity and apparent gain were too close to call which one was the winner. The 18 element yagi that was designed using the VK5DJ calculator could barely hear the signal source. I therefore measured the dimensions of this antenna, and realized I had built this antenna for the satellite portion of the band (1268 MHz). I will be redesigning another antenna using this design, but tuned to the proper frequency.

Keep in mind, this was a very unscientific test. I meant to do this to see if there was a noticeable difference in the performance of these antennas. Because I built the VK5DJ antenna some time ago, I hadnt realized it was built for the satellite portion of the band. I will run a new test on this antenna once it is built.

I printed out 2 different designs using the VK5DJ Antenna Calculator. One was for a 10 element yagi, the other for an 18 element model. The element lengths and spacing are identical for the first 10 elements, which suggests that a 10 element version could be built, and later the antenna extended to at least 18 elements at a later date. Therefore, I will construct the 10 element version, then will extend it at a later date, if the 10 element version checks out.

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