Original article from: Wayne Sarosi 
 Reposted by Rob Dennis,Moderator HAM_TECH,for use of the FIDO HAM_TECH echo.
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SUBJECT: Indoor antennas, 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 
op-
hat,but you can use anything that you can solder.
 I have a motorized discone in the works.
 A stepping motor will be incorporated to change the gap,to match the
frequency,for best SWR.
-WS
--- GoldED 2.42.G1219
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