-=> On 11-30-96  01:26, George Vaisey said to Ivy Iverson,<=-
-=>"About Mufu????????????????????...,"<=-
 
Hi, George;
 
 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, 156 MHz business band and UHF.
 II> Anyone interested in details?
 GV> Yes.  I'm interested in details.  Send them either here or below.
 
Sure.  I don't have Internet access and since I'm sure there are others
in the echo who would like to try it, I'll answer here.
 
(Semi-hidden: It doesn't L00K like an antenna.)  :-}
 
Materials needed:
 
Wire: Just about any kind.  # 16 or 18 insulated copper, either solid or
      stranded will work great, but it needs to be insulated.
 
Coax: I am currently using 72 ohm TV antenna coax, but foam RG-8, or
      even RG-58 would probably work slightly better.
 
PVC pipe: Just about any diameter that will easily contain the wires plus
          about 25-50%.  (I'm using 2" diameter)
 
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 inside.
 ³ ³³³ ³      (I use R.S.  Connect the center conductor to the upper set of
 ³ ³³d ³      model #      elements, and connect the shield to the lower
 ³ ³³  ³      15-1113B     set.  Make sure they don't short together.
 ³ ³³  ³      VHF-UHF TV
 ³ ³c  ³      amplifier)   Suspend the antenna assembly from the top of
 ³ b   ³                   the pipe using insulated cord. (I use 20 Lb.
 ³     ³                   test fishing monofiliment). ANCHOR THIS WELL TO
 ³     ³                   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 in 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
                           lengths, which will work fine for scanning.
Use tape, "Dux-Seal or"    Exact total length in feet for a given
"Coax-Seal" to water-      frequency can be calculated from the formula:
proof the coax hole.
                                                463
Aprox. element lengths:                      L= ---
 Band (MHz):  Each Leg:  Total Length:           F
      40 MHz  5' 8"      11' 4"
      2M Ham  1' 7.5"    3' 3"            Where L = Length in feet and
    160 MHz.  1' 5.5"    2' 11"                 F = Frequency in MHz.
 420 MHz Ham  0' 6.7"    1' 1"           Remember, this is total length for
    454 MHz.  0' 6.1"    1' 0"           each dipole.  Each element would
    920 MHz.  0' 3.1"    0' 6"           be half of the length shown by the
                                         formula.
(Calculations were done on the
"K2TV Antenna Calculator" pgm).
 
Assembly: Drill a hole in the side of the pipe about 1/2 the length of the
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 and feed it in toward the top
end of the pipe.  Connect a small weight, (Non metallic preferred but a
1/4-20 nut will work), to the bottom part 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, run
coax inside, connect and start scanning.
 
Catch you later, George.  Let me know how it works for you.
   Ivy
 
 
 
... Medics wear gloves so they don't leave fingerprints!!!   :-}
 
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