We are confining our design space to an inverted-L at this time. I did manage
to achieve 200 kHz (2:1 VSWR) in simulation for a 45 foot tall inverted-L
having a ground loss of 4 ohms. I can fire up a working model at a few hundred
MHz this week (initially without the impedance transformation). I don't know
that Dave wants to build this particular model as it is essentially a flat
sheet (made of many wires) 50 feet across for 1.9 MHz. However, with a 12 foot
wide inverted-L the 2:1 VSWR bandwidth is 100 kHz and going with a 16 foot wide
gives 125 kHz. I have incorporated the impedance transformation into the basic
design so we do not need any bandwidth robbing L-network.
The antenna ends up quite similar to a couple I have designed for commercial
use. The new part is the modification of the impedance transformation to allow
one to select the integer step-up ratio without regard to the physical antenna
width.
I did experiment with shunt T-lines and LC networks for further extending the
bandwidth (using WinSmith). I do see the double VSWR hump and I do see a modest
increase in bandwidth. However, the slightest loss really extends the bandwidth
and I suspect this is what many find. I think we will avoid this route.
Dave WX7G
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