From: Tony <dxdx@optonline.net>
To: towertalk@contesting.com
Sent: Wednesday, March 2, 2016 4:50 PM
Subject: [TowerTalk] Doublet vs Yagi
All:
I have a flat-top doublet approximately 100 feet long with it's apex 30
feet above the ground. It's fed with 300 ohm ladder line. I also have a
20 meter, 5 element mono-band Yagi that's twice as high at 60 feet above
ground.
When comparing the Dx reception of the two antennas, the signal strength
on the Yagi is many S-units above that of the doublet, but there is one
30 degree swath of azimuth where the doublet is only an S-unit or 2
below the Yagi.
The direction where the doublet has the most gain centers about 20
degrees off the wire dipole itself so it's far from broadside. It's as
though the gain exists close to where the greatest null should be; off
the end of the dipole.
My question is: what's most likely to cause the doublet to have that
much gain in one particular direction? Is it the terrain, the electrical
/ physical properties of the doublet, the signals angle of arrival or
some interaction with the two antennas?
I should mentioned that the Yagi sits 40 feet behind the doublet in the
direction where the doublet shows the most gain. Someone suggested that
the ladder line may contribute some vertical component that helps
reception.
Thanks,
73, Tony
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