Revised 14 June 2003
E-2
6. The design of the feed system rigidly enforces precise electrostatic balance for the
array. Balance is maintained with regard both to the feedline connection and to the
connection to the tower. This makes the antenna much quieter on receive and
eliminates the need for a separate BALUN or coil of coax in the feedline to the
transmitter. This balancing and matching scheme can handle virtually unlimited
amounts of power (in amateur radio terms) without any non-linear effects or failure
due to heating. It will “loaf” along at 5 kW CCS even on a full-carrier mode such as
radio teletype.
7. The feed system connects the elements to local RF ground (the support boom) for
low frequencies and DC. This feature permits the array to drain off static charges,
survive lightning hits, and provide useful non-radiative top loading of the tower
structure if required.
8. The feed system provides a high quality DC short across the feedpoint at the antenna
end of the feedline.
A schematic representation of the N7CL feed system for the two element driven array is
shown in Figure 1-E.
Front (shorter) Element
100 ohm balanced phasing
line formed from two equal
lengths of 50 ohm coax
Rear (longer) Element
Movable short permits easy
adjustment of stub reactance
for perfect match to 50 ohm
feedline to transmitter
Movable short permits easy
adjustment of stub reactance
Shorted open wire transmission
line used as hairpin inductor
RF "neutral" points
(all occurrences)
ground to element
support boom
Unbalanced
50 ohm
feedline
connection
point
50 ohm coax inside one arm
of hairpin forces balanced
antenna feedpoint to
unbalanced coax feedline
transformation
Figure 1-E
