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porta-j.txt

Found at: 0x1bi.net:70/textfiles/file?hamradio/porta-j.txt





                  BUILDING THE "PORTA-J" (patent being pursued)
                          By: N4VQT September 20, 1989


         The following are material's and cost's for building the
         "PORTA-J" the way I did.  If you feel you can cut corner's,
         or if you already have some of the materials, you should save
         some money.


          1) 1 telescopic antenna 72" total extended length
             (available from Radio Shack) .....................  $3.99

          2) 1 telescopic antenna 30 1/2" total extended length
             (available from Radio Shack) .....................  $2.99

          3) Antenna Bracket - a piece of 1 1/4" X 1/8" X 1/2" steel
             stock. (I used a piece of chain link fence stretcher which
             comes in 4' lengths and cut a piece to 1 1/4") Any suitable
             steel metal with these demensions will do.

          4) RG 58/U Coax cable about 12 - 18 feet in length.  (I used
             anywhere from 8 to 20 feet on the "PORTA-J's I built so
             this measurement is totally up to you) ............ $2.40

          5) BNC Connector for Handy Talkie connection or PL-259 for
             SO-239 Connections. ............................... $2.99

          6) Round head machine screws # 4-40 X 1/2" available from
             Radio Shack part # 64-3011.  (4 required).......... $1.19

          7) Steel Machine Hex Nuts # 4-40 available from Radio Shack
             Part # 64-3018.  (4 required) ..................... $1.19

          8) A .10oz tube of "Super Glue".  .................... $0.99

          9) Devcon Quick dry 5 minute Epoxy 1oz.  ............. $2.19

         10) A 16oz. can of PLASTI-COAT.  (available from Northern
             Handyman.  I've also heard that some Ace hardware store's
             carry it) ......................................... $7.99

         11) Electrical Solder.  ............................... $1.59

         12) 1/2" plywood which will be cut to 4" x 4".  Plywood must
             be smoothed on one side for finishing.  ........... $1.00

         13) THUMB SCREW 1/4-20 x 1/2" Hillman Part # J587 available
             from Ace hardware.  ............................... $0.25

         14) TEE NUT FASTENER 1/4-20  5/16" x 3/4" Hillman Part #
             E2505 available from Ace hardware.  ............... $0.20

         15) Small quantity of Minwax wood stain.  ............. $1.00

         16) Spray can of high gloss Polyurthane.  ............. $2.69

         17) 5" x 5" piece of felt.  ........................... $0.50

                                     Page 1







         18) Elmer's Glue 1 1/4 oz.  ........................... $0.69

         19) Small quantity of lacquer thinner for clean-up.  .. $1.00

         20) Small quantity of paint thinner for clean-up.  .... $1.00

         21) Masking or Scotch tape. ........................... $0.50


         Total Parts:  ........................................ $36.34
         Sales Tax @ 5%:  .....................................   1.82
                                                                 -----
         TOTAL INVESTMENT: .................................... $38.16

         Tools Required.

          1) Bench grinder.  (If you don't have one, a good steel file
             will do but a little more work will be required)
          2) Electric drill.
          3) 1 - 7/64" Drill bit.
          4) 1 - 3/8" Drill bit.
          5) 1- 7/8" wood bit.
          6) Single sided razor blade.
          7) Large empty band aid can.
          8) Pliers.
          9) Screw driver.
         10) Bench vise.
         11) Soldering Iron - 100 watt.
         12) Measuring tape.
         13) Steel file.
         14) 2" paint brush.
         15) Saber saw.
         16) Hack saw.
         17) Medium grade sandpaper.
         18) Narrow tip hole punch.
         19) 146 Mhz SWR Meter.
         20) Scissors.
         21) Tin snips.


                             ASSEMBLY INSTRUCTIONS

         1) Prepare antenna's for soldering of coax leads.
            (Figure # 1)

         Measuring from the bottom of each antenna make a mark exactly
         2 1/2 inches up for a filing reference point.  Using the side
         of the file, scuff off about 1/4" of the chrome plating to
         expose the brass antenna material beneath.  Make sure you
         file completely around the antenna's.  Be careful not to file
         too deeply as you may weaken the antenna's strength.  When
         completed, BOTH antenna's should have a 1/4" band of brass
         exposed and located 2 1/2 inches up from the bottom.  Using
         the 7/64" drill bit, re-drill the bottom holes in both
         antenna's.  This is to allow the antenna's to accept the
         machine screws.


                                     Page 2






         2) Prepare Antenna Bracket.  (Figure # 2)

         Measure part # 3 for correct size.  You may have to fabricate
         this piece out of scrap metal.  Keep in mind that whatever
         you decide to use, MUST be strong enough to support both
         antenna's as well as securing the antenna (once completed) to
         the mount.  Place both antenna's on the outer side of the of
         the antenna bracket and using a punch with a narrow tip,
         punch a whole for each antenna in the bracket.  Drill out the
         holes with the 7/64" drill bit.  Next, the thumb screw (part
         #13) must be smoothed on one side so it will fit perfectly
         flat on the bracket (you can use a bench grinder to do this
         or a file and elbow grease).  Punch two holes in the wing
         portion of the thumb screw and drill them out with the 7/64
         drill bit.  Place the thumb screw in the center on the bottom
         of the bracket so it is opposite the antenna's (facing down).
         Punch out two more wholes in the bracket using the drilled
         holes in the thumb screw as a guide.


         3) Assemble the antenna's and thumb screw to the antenna
            bracket.  (Figure # 2)

         Assemble the antenna's and thumb screw to the antenna bracket
         with the machine screws and nuts (part #'s 13 & 14).  Be
         certain that these nut's and bolts are as tight as you can
         get them!  Take care NOT to strip them.  After tightening
         the nuts, grind down the portions of the machine screws that
         extend beyond the nuts.


         4) Attach coax to antenna.  (Figure # 3)

         Strip one end of the RG/58U coax about 2 inches.  Peel back
         the shielding all the way to the black outer insulator of the
         coax to expose the center conductor and insulator.  Twist the
         shielding into a solid stranded wire.  Strip the center
         conductor about 3/4".  Using masking tape, tape the coax to
         the LONG antenna on the inner side.  Make sure you tape the
         coax so that the shield can be wrapped around the LONG
         antenna at the point where you filed it in step #1.  Wrap the
         shield of the coax completely around the antenna (you should
         have plenty of excess shielding but don't cut it off until
         you've finished the soldering connections.  BEFORE YOU
         SOLDER, MAKE SURE YOU EXTEND THE ANTENNA'S SO YOUR NOT
         HEATING MORE METAL THAN YOU HAVE TO!  Solder the shield to
         the LONG antenna and the center conductor to the SHORT
         antenna.  The center conductor (like the shield) must be
         soldered on the brass filed portion on the SHORT antenna and
         must be perfectly horizontal to to the shield connection.
         This solder connection will not only provide for the proper
         match but will also govern the distance between the two
         antenna's.  Therefore, it is IMPORTANT to measure the
         distance between both antenna's to ensure the exact distance
         is maintained for the entire length of the antenna's.  After
         letting the solder connections cool, cut off any excess
         shield or center conductor wire and file down any high solder

                                     Page 3






         spots for a smooth finish.  Now you can remove the masking
         tape which held the coax to the LONG antenna.  Bend the coax
         around the bottom of the LONG antenna so that it is perfectly
         perpendicular the the antenna.  Run a bead of super glue
         between the coax and the long antenna and the antenna bracket
         to ensure a tight fit of the coax to the antenna and the
         antenna bracket.  Hold in place about 1 minute to allow super
         glue to dry.


         5) Antenna re-enforcement.

         Now that the basic antenna is functionally complete, mix up a
         small batch of quick drying (5 minute) epoxy cement.  Place
         the epoxy cement on ALL screw and nut connections, and the
         coax to the antenna.  Give everything at least one good coat
         and allow it to dry.  The center conductor will need to be
         coated about 3 times to give the antenna the support it needs
         to maintain the correct parallel distance between the two
         antenna's. The 5-minute epoxy will cure relatively fast so
         you can apply the second and third coat's within 5 minute
         interval's.  Set the antenna aside and allow it to cure for
         another 30 minutes.


         6) Base mount assembly.  (Figure # 4)

         Locate the 4" x 4" x 1/2" piece of plywood and mark a hole
         exactly in the center on the BOTTOM side of the wood.  Using
         a 7/8" wood bit, drill a hole about 1/16" into the plywood.
         this will act as a recess lip so the nut fastener does not
         protrude passed the surface once it's installed.  Complete
         the rest of the drilling with a 3/8" drill bit for the nut
         fastener.  Using a hammer tap the nut fastener into the base
         mount from the BOTTOM.  Mix up another small batch of epoxy
         and secure the nut fastener with the glue.  Do not allow the
         glue to extend past the bottom surface of the mount.  If it
         does, you can sand it after it dries.  Completely sand the
         top and side surfaces of the base mount and apply stain and
         Polyurthane as per instructions on can - allowing sufficient
         drying time between applications.  Once dry, coat the BOTTOM
         of the base with a fine coat of Elmer's glue and lay a piece
         of felt approximately 5" x 5" on the glued side of the base
         mount.  After sufficient drying time, you can cut the excess
         felt off with a pair of scissors.


         7) Plastic coat laminate

         Open the can of plastic-coat and pour it into the large band-
         aid tin box.  grasp the antenna and dip it into the plastic
         dip and completely submerge the antenna about 1 inch above
         the center conductor.  Remove the antenna SLOWLY from the dip
         to avoid runs.  As soon as the antenna coax clears the top of
         the can, immediately pull the coax perpendicular to the
         antenna so that the plastic coating dries with the coax in a
         perpendicular position.  You will have to dip the antenna
         three time for best results.  Allow 20 to 25 minutes between

                                     Page 4






         coats.  The plastic coat will start to skin immediately and
         you don't have much time to play.  For complete curing, allow
         4 hours per coat to dry.  After the antenna has dried
         completely, you can trim the excess plastic coating from the
         top portion of the antenna's with a razor blade.  You will
         also need to trim off ALL plastic coating from the mounting
         screw (thumb screw).


         8) Standing Wave Ratio and Antenna tuning.

         Using a suitable washer, attach the antenna to the mount and
         stand upright on a desk or table in the room.  Install the
         BNC connector to the end of the coax and attach the BNC
         connector to a good SWR meter.  Connect your 2-Meter rig to
         the transmitter side of the SWR meter.  Extend both antenna's
         to their fullest and using the top portions of the whip's,
         adjust the LONG antenna to 58 inches from the top of the BASE
         and the SHORT antenna 22 inches form the top of the BASE.
         Power up the 2-meter rig and check SWR on 144 Mhz and 148
         Mhz.  Note the readings.  If the SWR is higher on 148Mhz than
         it is on 144Mhz, SHORTEN the SHORT antenna about 1/8" and re-
         check SWR.  If the SWR is lower on 148Mhz than it is on
         144Mhz, LENGTHEN the SHORT antenna about 1/8" and re-check
         SWR.  Continue until you find a happy medium.  I was able to
         attain a 1:1 SWR on 146Mhz and a 1.3:1 on 144Mhz and 148Mhz
         with 45 Watts into the antenna.  Be sure to check the SWR in
         different locations in the room as it may change nominally
         and you can make it as perfect as you wish.  It is better to
         have a higher SWR on 148Mhz than on 144Mhz since you can
         always shorten the antenna (if you have to) but if you cut
         too short you will not be able to lengthen the antenna.  A
         good rule of thumb, would be to achieve a 1.2:1 SWR on 144Mhz
         and a 1.4:1 on 148Mhz.  Once you've found the correct length
         of the antenna's, measure them from the top of the base and
         WRITE DOWN these measurement's.  Next, extend both antenna's
         to their fullest and mark them as per the measurements you've
         just written down.  Using a pair of tin snips, cut both
         antenna's to their proper length.  Next, put the two end
         pieces you just cut off the antenna in a vise and heat the
         end as close to the plastic tip with the soldering iron.
         While applying the heat, use a pair of pliers and pull the
         plastic end caps off the excess pieces of antenna's.  Round
         off the antenna's where you cut them so that the end caps can
         slide easily onto the antenna's.  Mix up a small batch of
         epoxy and glue the end caps to the tops of the antenna's.
         After sufficient drying time, dip the two end cap's in the
         plastic dip.  Again, three coats are required.  The plastic
         dip provides a certain amount of shock protection as well as
         adds to the overall appearance of the antenna.


         I've had excellent result's using this "PORTA-J" in various
         hotel rooms throughout the country and it fit's very nicely
         into my brief case along with my H/T and of course my
         business paper's.  It also works great on the beach, or
         anywhere you need an "instant" base station antenna without
         the need for a ground plane.

                                     Page 5






Figure # 1  Antenna preperation




                             │ │
                             │ │
                             │ │
                             │ │
                             │ │       │ │
                             │ │       │ │
          ------------------ │x│       │x│ < -- File off chrome plating
          |                  │ │       │ │      at two points marked with
          |                  │ │       │ │      "x" completely around
          |                  │ │       │ │      antenna's - about 1/4"
          |                  │ │       │ │      width.
         2 1/2 "             │ │       │ │
          |                  │ │       │ │
          |                  │ │       │ │
          |                  │ │       │ │
          |                  │ │       │ │
          |    7/64" hole -->│O│       │O│ <-- 7/64" hole
          -----------------  └─┘       └─┘








Figure # 2  ANTENNA BRACKET



                             │ │
                             │ │       │ │
                             │ │       │ │
                             │ │       │ │
                             │ │       │ │
                             │ │       │ │
                             │ │       │ │
                             │ │ Thumb │ │
                             │ │ screw │ │
                             │ │   │   │ │
                            ┌│ │───┼───│ │┐ --------------------
                   ┌───────>││O│   │   │O││<────┐              |
        7/64" hole │        │└─┘┌─────┐└─┘│     │ 7/64" hole  1/2"
                   └────────│──>│O   O│<──│─────┘              |
                            │   └─┐ ┌─┘   │                    |
                            └─────│ │─────┘ --------------------
                            |     │ │     |
                            |     └─┘     |
                            |             |
                            |----1 1/4"---|











Figure # 3  COAX Connection


                             │ │ Maintain exact distance between the two
                             │ │ antenna's at top and bottom (points a & b)
                             │ │a<───>b│ │
                             │ │       │ │
             Shield ────────>│──┐┌───────┤<── Center conductor
                             │ │││     │ │
         Apply "super glue"  │ │││     │ │    Apply several coats of epoxy to
         between antenna and │ │││     │ │    center conductor for stabiliy.
         coax to keep it in  │ │││     │ │    Apply 1 coat of epoxy to all
         place while epoxy   │ │││     │ │    screws and nut's as well as
         dries.              │ │││     │ │    the coax to the LONG inner side
                             │ │││     │ │    antenna.
                             │ │││     │ │
                            ┌│ │││─────│ │┐
                            ││O│││     │O││
                            │└─┘││────┐└─┘│
                      ──────┴───┘│   O│   │
        Coax ───────> ──────┬────┴┐ ┌─┘   │
                            └─────│ │─────┘
                                  │ │
                                  └─┘


Figure # 4  BASE MOUNT


                               Bottom view

                         ┌──────────────────────────┐ ----
                         │                          │    |
                         │                          │    |
     7/8" hole recessed  │        ┌──────┐          │    |
     1/16". -------------│------->│  ┌┐  │          │
     3/8" hole drilled---│--------│->└┘  │          │    4"
     completely thru     │        └──────┘          │
     plywood.            │                          │    |
                         │                          │    |
                         │                          │    |
                         └──────────────────────────┘ ----
                         |                          |
                         |                          |
                         |---------- 4" ------------|

       Insert Tee Nut Fastener through bottom of base mount and apply a
       thin layer of epoxy to secure the fastener to the base mount.



   Well, there you have it!  I'm sure this great little 2-Meter
   "PORTA-J" antenna will provide you with years of happy Hamming!

   Good Luck,
   Rick Yost  N4VQT  (SYSOP - NETWORK BBS)
   Raleigh, NC

  PS. If through your effort's you stumble on a better way to build
      the "PORTA-J", or you find a way of increasing it's gain,
      please let me know by leaving me an E-mail message on the USPS
      Network Bulletin Board at (919) 878-5116 or 5114.  Thanks!


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