At 08:01 AM 8/24/2006, Joe Subich, W4TV wrote:
>Larry,
>
>Looking at the (sparse) information available on the SGC web site.
>it looks like the SGC-103 and SCG-104 are classic "wideband folded
>dipoles." The length is given as 90 feet (27 meters) and frequency
>coverage is given at 2-28 MHz. Both of those match the classic
>WBFD numbers and the drawings appear to be much like the others.
>
>I need to play with EZNEC a while ... given the complexity of the
>WBFD (18:1 transformer and high power loading resistor), I wonder
>if it would not be possible to construct a G5RV like antenna with
>parallel wires (spaced 2 feet) that would have low SWR on all the
>amateur bands between 3.5 and 30 MHz. It would not fill the need
>of commercial/military for an ALE ready antenna but it would be a
>"cheap and dirty" antenna for amateur use that would not incur
>the 3 to 6 dB penalty from the WBFD "terminating resistor."
I spent a while trying to figure out a set of lengths for a multiband
dipole (think in terms of the DX-CC from Alpha Delta) that would cover all
the SHARES frequencies (which are fairly close to the ham bands) and I kept
coming up with one or two bands that you just couldn't "get there from here".
You can find a set of lengths that does 40,20,15, and 10 just fine (15 is
third harmonic of 40, etc.), but picking up 12 and 17 and 30 is difficult.
This is especially true if the installation had to be flexible (i.e. you
can hook it up as a inverted V or as a flattop or as a sloper... all of
which are possible with the resistively loaded antenna).
However, I didn't spend much time on it, and I couldn't get my optimizing
engine at the time to work right (otherwise, it would just be a "let it
grind over the weekend" kind of task).
Jim
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