Topband: "T" or Inverted L?

[Bill Tippett]

AE5X wrote:

>Am I right in assuming that since the top part of the T does not radiate
>that the vertical section of the T needs to be longer than the vertical
>section of an Inverted L for a given freq? If so, which is the preferred
>antenna (for DX) with a maximum vertical section of 60 feet?

        You can vary the length of the T to work for any height.  Always
go for maximum vertical component whichever one you decide on.  The L has
a slight directivity advantage over the T for a given height, so an L could
be the better choice IF your objective is in a given direction (BTW the 
directivity is in the direction 180 degrees opposite to the direction the
horizontal part runs!)  For a given vertical height, I would always go with
a T since it is omnidirectional and minimizes high angle radiation.  

>And how do you calculate the length of the top section (of a T) for a
>given vertical dimension?

        A quick model using EZNEC shows a 60' high Tee with each side 49'
long resonates on 1830 with an impedance of 16.5 ohms resistive.  You will
need to "cut and try" to get it exactly right but 49' should be a good
starting point...and of course you will need a matching transformer at
the base.  Remember the MOST important part of a T or L is the ground
system...60 1/4 wave radials will work well.

                                                        73,  Bill  W4ZV



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