Topband: "T"-Top Vertical Antennas

[Paul Christensen]

> antenna as a flattop radiator, fed by a vertical wire.  Most
likely they didn't realize it was their "feeder" doing all the work
and the flattop radiation was being cancelled out !

By 1921, they knew the importance of the flat-top as a non-radiating loading 
device to increase radiation efficiency.   The theory of the Marconi "T" and 
its variants was pretty well understood by J. Fleming during the time of 
Marconi's transatlantic tests.  Fleming was responsible for the design of 
Marconi's Poldhu transmitting station ca. 1900-1901.  I've seen several 
early references to the use of top-loading with single wire "Ts" and the 
more prominent multi-wire flat-tops.  These typically employed 4-6 wires.

In reading through some materials from R.H.G. Matthews, owner of 9ZN in 
Chicago, early spark stations generally employed one device to determine 
antenna radiation efficiency :  An R.F. ammeter placed in series with the 
vertical portion of the antenna offered the clue.  The multiwire "T" evolved 
as a result of the ammeter.  As more wires were added to the flat-top, the 
ammeter displayed more current.  Horizontal wires would be added to the 
point of reaching diminishing returns as measured on the ammeter.

Paul, W9AC