Tuesday, July 14, 2009

10 Element 1296 Yagi Works!

Just finished building and tested a 10 element yagi for 1296. This antenna replaced the larger yagi that did not appear to work. This one received the source just fine. Being it is only 21 inches long (boom length), it did not perform like the 4 foot long antennas that I had tested earlier, it still seems to have the gain and directivity that I would expect out of a 10 element yagi.

The software that I used to design this antenna suggests that the antenna can be lengthened without having to change the current element lengths or spacings. Therefore, I'll add another segment to this antenna at a later time to increase its size to something that should be more useful.

This antenna was a new design, as I used very small diameter elements (1/16 inch). Most yagis on 1296 use 1/8 inch elements, which in my opinion might be a little large for this band. Although the software can design working antennas with different diameter elements, I went with 1/16 inch aluminum to keep the weight down, and I'm thinking the thinner elements might provide a little more gain.

The next step is to get these antennas tested for return loss. I still have no idea how they perform in that manner, and do not have the instruments to test. I did run across an article online telling how to build a directional coupler that works from 2 meters up thru 1296, which I just might decide to build. I think I have all the necessary parts to build it.

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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