At 05:13 AM 8/24/2006, Larry Phipps wrote:
>I recently read that, Joe. L.B. confirmed my assumptions, but it's nice
>to see a somewhat rigorous treatment. Do you know if the SGC broadband
>dipole is basically the same design?
I think we need to distinguish between this antenna and the SGC broadband
whip is actually two whips in one (conceptually its two helically loaded
antennas on the same form, with different winding pitches, designed to
provide an acceptable match to their tuner over the wide range of
frequency. I've seen a fixture that puts two SGC whips back to back with
the tuner in between, and then the whole assembly is hoisted up a pole.
The broadband dipole (SG103/SG104) is just like the B&W unit (on which the
patent has long expired), and , I'm guessing, is a product developed to
meet a procurement requirement so they can sell a package of radio and
antenna. I can see the procurement request:
1 each Radio, Manpack, HF
1 each Antenna, Broadband, must provide 2:1 VSWR or better over specified
Antenna, broadband, folded dipole, with end supports XXX inches long,
center support YYY inches, etc.
The 103 is the 150W peak, and the 104 is the 1kW Continuous unit.
$250 for the lower power version seems a plausible price..(they don't have
a price for the SG104) I wonder, how much power does the load have to
dissipate? I guess I can fire up Cebik's model and measure it. AS Cebik says:
"Locating a non-inductive resistor of sufficient power dissipation is
likely to be the chief problem for WBFD builders who intend to transmit
with the antenna. Unless you can find a suitable resistor at one of the
surplus outlets, purchasing an antenna may prove economical in the long
run, if we add both cost and parts-searching time together. Any value in
the 800-900 Ohm range--or even "thereabouts," if a bargain appears--will
And then, there's the RF transformer.
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