[amsat-bb] Re: Arrow and ELK Comparative Antenna Tests

[Mark L. Hammond]

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
>_______________________________________________
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