Hi Bruce,
I'm using 3 small Pennant RX antennas (51.6% the size of full size
pennants), one pointing 40 degrees, one pointing 160 degrees, and one
pointing 300 degrees (sharing the same feedpoint). Originally bottom of
them were 2 feet off the ground and then after a year of encouragement from
my wife I raised them up so the bottom are 8 feet above ground.
My buried radial field (55 short radials, average length 60 feet) runs
right under my pennants, and my 68 foot base loaded TX vertical is
approximately 40 or 45 feet (as I recall) from the feedpoint of the
pennants.
No difference in performance between the 2 foot and the 8 foot above ground
mounting positions (no noticeable difference in signal to noise using my TX
vertical as a reference antenna for signal to noise improvement, and no
noticeable difference in front to back ratio).
Originally I took steps to detune my TX antenna during receive, but to my
surprise detuning was not necessary on 160 meters in my installation. On
the other hand something is destroying the pattern (noticeable on front to
back) of my pennants when used on 80 meters, and detuning of my TX antenna
helps slightly, but the TX antenna is not the main cause of my 80 meters
problem (I even removed (took down) my TX antenna to make sure it was not
the TX antenna causing the problem). I've always suspected the problem is
the proximity of the RX array to my house and interaction with house
wiring, rain gutters, metal I beams, metal chimney flue, etc, but never
considered the ground radials. Since my primary interest is 160 meters I'm
very happy with my system (installed summer of 2011).
This morning I recorded AA1K calling CQ on 160 meters and uploaded the
recording to youtube so you (and others) can experience one example of the
directional properties of my pennants. Since my pennants are not pointing
exactly 180 degrees from each other it's impossible to fully capture the
front to back properties, but you can certainly compare the performance to
the expected plots of my array. There was a lot of QSB during my
recordings this morning, and suspect (based on the variation in front to
back ratio during the recording) that the arrival angle was changing
considerably over time but the QSB might have also been due to a different
propagation phenomena.
The youtube link for the AA1K recording is
http://www.youtube.com/watch?v=TWlBy5ypMIU
(Note : AA1K is 564 miles from my QTH at a heading of 93.6 degrees)
The link to my website where you can see the expected directional
properties (pattern plots overlay) when receiving AA1K from my QTH is
http://sites.google.com/site/pennantflagantennas/
You will definitely see periods where I'm experiencing 18 to 20 dB front to
back directional properties in the AA1K youtube recording (and AA1K is not
lined up exactly with the back of my 300 degree pennant), but then you will
also see times where the directional properties are much less. My plot
overlays predict approximately 15 dB in directional properties when
receiving AA1K (if arrival angle is 31 degrees), and think the 15 dB is
close to the average experienced in my recording.
Also on my website I show a plot for predicted front to back ratio versus
arrival angle for pennants, and think you will find this interesting (front
to back ratio is very dependent on arrival angle). On the average I would
say I notice front to back to be 18 to 20 dB if the back of one of my
antennas is close to being lined up with the station I'm receiving (not
exactly front to back since my antennas are not facing exactly 180 degrees
from each other, but close since the forward pattern is so broad).
Sorry for the long posting, but very complicated topic. I also have lots
of comments about the overall characteristics of pennants (performance
compared with a vertical TX antenna), but won't complicate this posting
with them.
73,
Don (wd8dsb)
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