-=> In a message to Glenn Fetty  Dominic Post wrote:
-=>"About Semi-hidden antenna...,"<=-
 
Hi, folks;
 
Ok, here it is for those who missed it the first time.
 
Multiband scanner antenna, origionally posted by myself on 12/2/96,
reposted 12/13/96 by request.  Updated with additional information.
 
 II> Scanner antennas: I built my own "semi-hidden" outdoor scanner antenna.
 II> It is a vertical wire dipole which has three separate elements: 2-meter
 II> Ham band, 160 MHz business band and UHF.
 
(Semi-hidden: It doesn't L00K like an antenna.)  :-}
 
Materials needed:
 
Wire: Just about any kind.  # 14 or 16 insulated copper is suggested.
      Stranded will be easier to assemble, but solid will work fine.
 
Coax: I am using 72 ohm TV antenna coax, but foam RG-8, or even RG-58
        should work about as well.  Keep the coax as short as practical to
        minimize losses, and run coax horizontally as far as practical
        from the antenna to miminize interaction).
 
PVC pipe: Just about any diameter that will easily contain the wires plus
        at least 50%.  (I'm using 2" diameter)  A pipe cap to close the
        top of the pipe is advisable.
 
Something to seal a hole: "Coax-Seal," "Dux Seal", tape or even bubblegum
        will work.  :-}   Tape can be used, but will eventually let go
        and come loose when exposed to the weather.
 
Coax connector: To suit your scanner, amplifier, (or splitter if feeding
        more than one scanner).
 
Tape: Plastic electrical tape.
 
Weight: A small weight - a few ounces.  Preferably not metallic but a
        1/4-20 nut will work ok.
 
Amplifier: I use a Radio Shack model # 15-1113B VHF-UHF TV amplifier.  You
        could also use an at-the-antenna UHF/VHF preamplifier inside the
        pipe and power it through the coax.
 
Fishing line: I use 20 Lb. test monofiliment.  Any similar non-metallic,
        non-rotting line will work to support top of antenna inside pipe.
 
Moderator: Sorry, I can't make this clear without using high-ASCII
characters.  My apologies.
 
 _______  <- Close top of pipe with pipe cap or weatherproof tape.
 ³\a   ³
 ³ \   ³                   Details:
 ³ ³b  ³                   The legs of all dipole HALVES are connected
 ³ ³³c ³                   together at the center end, and insulated from
 ³ ³³  ³                   each other from there to their ends.  Tape them
 ³ ³³  ³                   together using plastic, (NOT RUBBER!), electrical
 ³ ³³³d³                   tape.  If you are building a 2-band version, just
 ³ ÃÁÙ ³                   use common plastic lamp-type "Zip" cord and don't
 ³ Àðððððððððð> Coax to    "unzip" it.
 ³ ÚÅ¿ ³       amp or
 ³ ³³³ ³      scanner(s).  Connect the center conductor to the upper set of
 ³ ³³d ³                   elements, and connect the shield to the lower
 ³ ³³  ³                   set.  Make sure the top & bottom halves don't
 ³ ³³  ³                   short together!
 ³ ³c  ³
 ³ b   ³                   Suspend the antenna assembly from the top of
 ³ Û e ³                   the pipe using insulated cord.  ANCHOR THIS WELL
 ³     ³                   TO THE TOP OF THE ANTENNA!
 ³     ³                   
 ³pipe ³                   Run the coax horizontally out from the assembly
 ³/\/\/                    at a 90 degree angle as far as possible.
 
a = Fishing line to hang   NOTE: I do not recommend this antenna for
    antenna inside pipe.   transmitting unless it has been cut using the
b = Lowest freq. dipole    formula below and trimmed using an SWR bridge.
c = Medium freq. dipole
d = highest freq. dipole.  Element lengths: The chart shows aproximate
e = Weight - can be        lengths, which will work fine for scanning.
    almost any small       Exact total length in feet for a given
    item. See materials    frequency can be calculated from the formula:
    list.
                                                         463
Aprox. element lengths:                               L= ---
 Band (MHz):  Each Leg:  Total Length:                    F
27 MHz (CB)   8' 7"      17' 2"
      40 MHz  5' 8"      11' 4"          Where L = Length in feet and
      2M Ham  1' 7.5"    3' 3"                 F = Frequency in MHz.
    160 MHz.  1' 5.5"    2' 11"         Remember, this is total length for
 420 MHz Ham  0' 6.7"    1' 1"          each dipole.  Each element would
    454 MHz.  0' 6.1"    1' 0"          be half of the length shown by the
    920 MHz.  0' 3.1"    0' 6"          formula.
 
(Calculations were done on the
"K2TV Antenna Calculator" pgm).
 
NOTE: On the higher frequency bands, (particularly above 200 MHz), you may
get better reception if you make the legs an odd multiple of 1/4
wavelength, ie: for 920 MHz, a dipole 3' long with elements 18" long
instead of 6" total with elements 3.1" long.
 
ASSEMBLY: Drill a hole in the side of the pipe 1/2 the length of the
longest dipole plus a couple of inches below from the top of the pipe.
Make this hole large enough to feed the antenna wires through.  firmly
connect the fishing line to the top part of the antenna, (the end
connected to the center conductor of the coax), and feed it in toward the
top end of the pipe. Connect the weight to the bottom end and feed it all
the way into the hole, aiming it toward the bottom of the pipe.  Pull the
fishing line from the top of the antenna up to the top so that the hole in
the side of the pipe lines up with the feed point of the antenna, anchor
it and seal the top and hole against water.  Put it up in the air away
from metal.  Keep the part of the pipe with the antenna inside as far as
possible from any metal, run coax indoors, connect and start scanning.
Make sure there is some way for water which will get into the pipe to
drain from the bottom.  (Easy way: leave the bottom open).
 
(c) 1996 T.M.I.Iverson
 
Catch you later.  Let me know how it works for you.
   Ivy
 
 
 ... What's a mischievious Amateur Operator?  A Deviled Ham!
 
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