* Originally By: Wayne Sarosi
 * Originally To: All
 * Originally Re: [Indoor antennas - part 3
 * Original Area: Ham_Tech
 * Forwarded by : Blue Wave v2.12
SUBJECT: Indoor antennas part 3, VHF/UHF Discones
       The discone antenna is a rather unique antenna for VHF and UHF.
The discone has no gain to speak of, yet can provide the user with a
range of ten times the design frequnecy for reception and transmitions.
This means that a discone designed at 140 MHz will work fine up to 1.4
Ghz.
       Hiding the discone outside may prove to be quite a feat.  Unlike
most antennas, the discone has a large skirt and is tall to boot.  It's
shape can draw attention.  If you can place the antenna outside, it will
give you excellent coverage over it's range.  Inside, the discone works
well
minus the attenuation caused by the building it's in.
       There are many Discones available on the market if you choose not
to 
build one.  Building one can be fun if you take the time and lay
everything
out ahead of time. 
       There are a couple items I would like to point out about discones.
       1) The gap between the top-hat and the skirt is critical.
       2) The area under the skirt is a null to the antenna.
       Design parameters are easy.  
       o   The top-hat diameter is:   (0.1778 * (984/f MHz))*12
            EX: at 140 MHz -->  (0.1778 * (984/140))*12) = 15-in
       o   The diameter of the skirt, at the base, equals the length of
           the skirt elements.  This gives the user the closest impedance
           to 50-ohms.  Thus a skirt element length is:
                        (0.2675 * (984/f MHz))*12)
            EX: at 140 MHz -->  (0.2675 * (984/140))*12) = 22.56-in
       o   The gap is:  (0.007114 * (984/f MHz))*12)
            EX: at 140 MHz -->  (0.007114 * (984/140))*12) = 0.6-in
       A tin funnel works well as a starting base that brass skirt
elements
can be soldered to. An SO-239 chasis connector can be fit into
the cutoff
funnel end and the top-hat soldered to the center pin of the SO-239. 
Insullating spacers can be used to strengthen the gap.  I've used a brass
screw that was soldered between the center pin and the top-hat, but you
can
use anything that you can solder.
       I have a motorized discone in works.  The stepping motor will be
incorporated to change the gap, to match the frequency, for best SWR.
-WS
-!-
 ! Origin: KB4YLY (Quick 1:374/73.2)
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