Topband: Inverted-L vs T Antenna

[Terry Conboy]

At 12:55 PM 2008-10-05, Garry wrote:
>Is there any advantage in using an Inverted-L if you have to run it up a
>tree where the vertical run is very close to the tree verses a "T" where
>the vertical portion would be in the clear between two trees for supports?
>
>Thanks,
>Garry - K4OR

In this situation, the inverted-L should have more high angle, 
horizontally polarized signals for short haul QSOs, but possibly more 
absorption in the closely spaced tree trunk and slightly lower gain 
at low angles, compared to the T.

The matching approach can be similar with either one:
1) Make the antenna somewhat larger than needed for resonance, such 
that the resistive component of the feed impedance is near 50 ohms, 
allowing matching with a simple series cap.
2) Make a little shorter than resonant and use a shunt coil (hairpin) 
to create a virtual L-network to step the Z up to 50 ohms.

Approach 1 is probably better with the T, since the high angle 
signals are attenuated due to symmetry and the efficiency (due to 
smaller ground losses) is better.  Either matching approach produces 
similar low angle gain with the inverted L (but more high angle 
signal is radiated with approach 1).

73, Terry N6RY