Thanks John and Patrick. Interesting results and a very nice study. Question---what was your testing method? I can't glean that from the information below.
Thanks! Mark N8MH At 08:49 PM 4/24/2011 -0700, John Kopala wrote: >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 AMSAT-BB@amsat.org. 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 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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
