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

Gary "Joe" Mayfield gary_mayfield at hotmail.com
Mon Apr 25 05:18:05 PDT 2011


      Thank you for your objective, scientific comparison!  I eagerly await
your article in the AMSAT journal ;-)  This is really good stuff.  If your
test stand is still available there is one more thing I would dearly love to
see tested.  Antenna guru Kent Britain, WA5VJB, once commented the Arrow
seemed to be designed for the elements to be insulated from the boom, and
there might be something to be gained from doing just that.  Testing the
Arrow with the elements in standard convention vs. insulated has been on my
to do list ever since but I never seem to be able to get around to it.

	Again just a thought, and thanks for your awesome work already!

Joe kk0sd

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of John Kopala
Sent: Sunday, April 24, 2011 10:50 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] Arrow and ELK Comparative Antenna Tests

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
Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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