On Saturday, April 23, Pat Stoddard (WD9EWK) and I did some antenna testing in an attempt to answer the questions about which is the best antenna for portable satellite operation. We only tested the antennas in receive mode to determine their relative gain. Time constraints prevented us from performing additional testing to determine if the transmitted output was consistent with the receive gain of the antennas. For the time being we will assume (and we all know the dangers of doing so) that the transmit performance closely matches the receive performance.
The antennas tested were an Arrow (3 x 7 elements), an ELK (4 elements), a PortaFox configured for 145/435 operation (4 elements), and a Home Brew 4 by 9 element "arrow" antenna. The standard Arrow antenna was the only antenna equipped with duplexer, but not the basic duplexer which is installed in the handle. We did not measure the insertion loss of the duplexer on the Arrow antenna, but this was obviously not a significant factor in the overall performance. A duplexer could still be required depending upon the antenna chosen and the radio(s) to be used. Using the Arrow antenna as the reference antenna and 145.300 MHz as our test frequency, our measurements indicated that the Arrow and the ELK antennas had identical gain. The PortaFox antenna showed 2db less gain than the Arrow and the ELK. The Home Brew 4/9 element crossed yagi showed 2db more gain than the Arrow and the ELK. On 435.300 MHz, the Arrow antenna had 2db more gain than the ELK and 8db more gain than the PortaFox. The Home Brew 4/9 element had 3db more gain than the Arrow. Although the ELK antenna shows slightly less (2db) gain on 435.300 MHz, it does have one potential advantage over the Arrow antenna. With the ELK, transmit and receive are in the same plane. With any satellites that have linear polarized antennas, such as AO-27, SO-50, the ISS and maybe SO-67, a crossed yagis can maximize the performance on one band while minimizing it on the other. That does not mean the Arrow won't work, as has been demonstrated by the thousands of satellite QSO's that are made on a regular basis using Arrow antennas. It just means that when you rotate the antenna to maximize the downlink signal, you may be significantly impacting you uplink signal strength in marginal situations. Even though a satellite may have a circular polarized uplink and downlink, don't assume that the orientation of your station antenna as horizontal, vertical, or something in between won't have a significant effect on your signal strength. My experience operating portable with my home brew antenna has convinced me that my horizontally polarized Qagi should either be remounted vertically polarized or replaced with a circular polarized antenna. That is another ongoing project. In summary, unless you plan to build your own, the performance of the Arrow crossed yagi antenna and the ELK log periodic antennas are very comparable and should provide lots of solid satellite contacts. The overall results reflect the adage that bigger is better, but along with more gain, you also get a more bulky antenna that is harder to handle. The home brew crossed yagi I built for portable operation is tripod mounted, can be rotated on its axis, and disassembles for storage in a roll up case. But because of its size, it would be very tiring to attempt to use it hand held for an extended period of time. Pictures of the home brew crossed yagi antenna are on my QRZ page. John Kopala N7JK _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
