> > At 01:07 PM 9/10/2003 -0400, Roger D Johnson wrote:
> > I toyed with the idea of feeding
> > >the elements in phase for transmit and with the delay for receive.
> > >It made the system a bit more complicated but resulted in better
> > >transmit signal while still having the F/B on receive.
>
Receive only arrays can be fed differently.
Last spring I put up an array of 1/8 wave spaced (32 ft)
verticals for 80 meters aimed at Europe. The verticals were
30 feet high and fed through 1:1 isolation transformers
located at the bases. Four 30 foot radials were used
for a counterpoise. The antenna side of each
transformers had a 50 ohm resistor across it. An broadband
electrical delay of 32 nsec was added to each front vertical
using a lumped element delay line (coax could also be used).
32 nsec is how long it takes a radio wave to travel 32 ft.
The front and rear vertical pairs were combined out of
phase with a 180 degree hybrid. The four pairs
were then combined with a 0 degree hybrid.
This kind of array not only works well across 80 meters, but
also has excellent F/B on 160 and even in the broadcast band.
I could listen to a station 1500 miles away on 940
kHz while rejecting a local on the same frequency
(they just happened to be in the right directions
for the array).
Note that the feed technique described above will
NOT work with full size verticals (ie 65 feet on 80 meters).
For example, my array stops working on 40 meters
because the elements are full size there.
Rick N6RK
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