[TowerTalk] Doublet vs Yagi

[Tony]

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