Topband: "T" Antenna

[RK]

Hi Guys,

I was away at work the last few days with no internet. Thanks, Rick for 
filling the gap! Rick's point about the horizontal component is correct. A 
slightly higher radiation resistance but not at the beneficial angle. I 
believe in NEC4 represents this better, but Rick's approach by mutual 
coupling points the right direction. The lengths of the loading portion of 
the "T" from the feedpoint to either end is very close to 1/4 wave. My 50ft 
verticals with twin sloping wires use loading wires of 75ft. They resonate at 
1.9 MHz. I use about 1.5 uh base loading to resonate them in the area of 
1.825 MHz. (64 radials or More) This is easily matched by a 1:4 UN-UN with 
very little loss.

The point that I was making that in a "T" or Marconi the polarization is 
vertical,  and the efficiency as compaired to a full 1/4 vertical by 
minimizing losses is much greater than using other loading methods. Example: 
large amounts of lumped constants to achieve resonance.

A "Marconi" antenna is actually any vertical antenna that is electrically 1/4 
wave resonant. A "L" antenna is not because of a substantial horizontal 
component. Early ship board and broadcast antennas were in the form of a "T" 
but still very much a Marconi. Before steel towers the top loading wires were 
usually supported between to large wooden structures.

73
-- 

Bob Kile, W7RH
DM35OS
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