J-Pole Antenna
                        by K4TAX
                     Pompano Beach, FL
Formula:
 Short element (2878/fMHz)                              146MHZ -> 16.71"
 Long element ((K*(5904/kMHz))+(2878/fMHz))             146MHz -> 56.39"
 Balun  (3897/fMHz)   based on velocity factor of .66   146MHz -> 26.75"
(K factor is ratio of diameter to wavelength)
To use a different coax velocity factor:
 (VF * 5904) =  Balun constant used in balun formula.
Construction:
 96" - 1/2" rigid copper pipe
 1   - 1/2" copper 90 degree elbow
 1   - 1/2" copper "T"
 2   - 5/8" hose SS clamps
 2   - 1/2" pipe caps
 1   - 1/2" copper to NPT adaptor
 1   - 1/2" deck NPT deck flange
 Clean all joints with stel wool or fine grit sandpaper.
 Using a propane torch, solder all joints using flux & plumbing solder.
           ____________________________
            |                             |
            |                             |
            |                             |
            |                             |
            |                             |
          56.39"                _ _____   |
            |                    |        |    |
            |                    |        |    |
            |                   19.71"    |    |
           _|____________________|_____   |____|
                                          |  ^
  NOTE: All measurements made from        |
        bottom of the "J"  (see ^)        |
Spacing between the long element and short element is not critical
but should be a MAX of 2".
(Join the T and the Elbow with a 1" length of pipe)
The base section below the "T" is the remainder of the pipe
after cutting the long and short element and the 1" piece
used to couple the elbow and the "T".
Final mounting can be accomplished by adding a 1/2" "sweat to NPT" fitting
at the bottom of the antenna and the using a deck flange for surface
mounting.
The feed point is approximately 3" from the bottom of the "J".
Connect the center wires of the balun to each element using a hose clamp.
Adjust the feed point up of down for the best match using a SWR bridge.
Keep each feed point at equal heights above the bottom of the "J".
Once the best SWR is found, mark the position, remove the hose clamp and
solder the wire to each element.  Use care so as to not overheat the
center conductor or dielectric of the coax.  The coax and balun shields
are not connected to the antenna.  Seal coax ends with BLACK silicone sealer.
CAUTION:  Outside installation of the J-Pole must provide a proper
ground for lightening protection.
Balun construction and wiring:
(use RG-8 solid dielectric coax)
                    | TO ANT.|
            ________|        |
           | .____. | .____. |    (Be sure to connect feed line shield
         | | |    | | |    | | |   to the shield at each end of the
         |   |    |   |    |   |   balun coax section.)
         |   |    |   |    |   |
         |   |    |   |    |   |
         |   |    |   |    |   |
         |   |    |   |____|   |
         |   |    |            |
         |   |    |____________|
         |   |
         |   |
         |   |
       Feed Line
        50 ohm
Note:
To minimize transmission line los on receive and transmit, only low
loss coax such as RG-8 solid dielectric or RG-8 foam dielectric
Hit  to continue or "A" to abort output. BBS commands are IGNORED 
ere!
coax should be used for the feed line.  Power handling ability of this
antenna has not been determined but is anticipated to be near 500 watts.
Coax balun is the limiting factor.  Antenna gain is calculated at 3dBd.
  ... _._
=========================================
73 = Best Regards                ka5thb@bigfoot.com
-Jeff KA5THB
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