[TowerTalk] horizontally polarized antennas and salt water

[Pete Smith]

At 01:53 PM 1/17/2005, Stephen Reichlyn wrote:


>Gentlemen and Ladies of Towertalk:
>
>Anecdotal comments about antennas and their performance by the sea are 
>many and sundry. I wonder if
>those who have experience with this phenomena can comments on the 
>following points:
>
>We have all read that vertical antennas work especially well on (or near) 
>the beach. I have first hand experience
>with this and certainly agree that this is the case. I often wondered 
>whether radials (even simple 2 wire systems)
>are really needed next to salt water.
>
>1.The ultimate question is 'what effect does the salt water have on 
>horizontally polarized HF antennas, if qny'?
>
>2. Do you think that tidal changes (for instance +/- 6 feet) in the near 
>field have an effect on angle of radiation
>of horizontally polarized antennas, such as yagis.
>
>3. How far away from the ocean (in miles) do you think the near field salt 
>water effect disappears?
>
>4. Or do you think that salt water near field has NO effect on 
>horizontally polarized antennas?

It does, but not a bunch.

I quickly modeled a 40m yagi at 104 feet over average ground versus salt 
water.  Forward gain went from 11.86 dBi (avg) at 18 degrees to 12.45 dBi 
(salt).  Takeoff angle, interestingly, went up one degree for the better 
ground plane.  Moving the antenna down 6 feet over salt water moved the 
takeoff angle up 1 more degree, from 19 to 20 degrees.

73, Pete