Topband: How much ground independence?

[Shoppa, Tim]

I found it very educational when setting up my K9AY loop, to listen to the PT0S pileups. It's what convinced me that I had done it "right" in building the K9AY.

Remote direction selection on the antenna worked a lot like an astronomical blink comparator: hearing which signals disappear, and then looking up headings using qrz.com and other online tools, helped me accurately locate the "true" directionality of my antennas.

The blink comparator is a very powerful tool (I think I was one of the last generations of astronomy grad students to be trained using the original hardware version... I think most folks since my generation use image differencing algorithms on the digital capture) for the eye. Similarly switching direction instantaneously and hearing which signals drop away and which ones come up, is a very powerful tool for the ear.

I will see if I can get diversity reception and get similar advantages.

Tim N3QE

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Don Kirk
Sent: Wednesday, December 11, 2013 11:16 AM
To: Bruce
Cc: topband; chetmoore
Subject: Re: Topband: How much ground independence?

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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