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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
<20> <20>
<20> <20>
<20> <20>
<20> <20>
<20> <20> <20> <20>
<20> <20> <20> <20>
------------------ <20>x<EFBFBD> <20>x<EFBFBD> < -- File off chrome plating
| <20> <20> <20> <20> at two points marked with
| <20> <20> <20> <20> "x" completely around
| <20> <20> <20> <20> antenna's - about 1/4"
| <20> <20> <20> <20> width.
2 1/2 " <20> <20> <20> <20>
| <20> <20> <20> <20>
| <20> <20> <20> <20>
| <20> <20> <20> <20>
| <20> <20> <20> <20>
| 7/64" hole --><3E>O<EFBFBD> <20>O<EFBFBD> <-- 7/64" hole
----------------- <20><><EFBFBD> <20><><EFBFBD>
Figure # 2 ANTENNA<4E>BRACKET
<20> <20>
<20> <20> <20> <20>
<20> <20> <20> <20>
<20> <20> <20> <20>
<20> <20> <20> <20>
<20> <20> <20> <20>
<20> <20> <20> <20>
<20> <20> Thumb <20> <20>
<20> <20> screw <20> <20>
<20> <20> <20> <20> <20>
ڳ <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ij <20><> --------------------
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>><3E><>O<EFBFBD> <20> <20>O<EFBFBD><4F><<3C><><EFBFBD>Ŀ |
7/64" hole <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ŀ<EFBFBD><C4BF>ٳ <20> 7/64" hole 1/2"
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD><C4B3>><3E>O O<><<3C>ij<EFBFBD><C4B3><EFBFBD><EFBFBD><EFBFBD><EFBFBD> |
<20> <20>Ŀ <20><><EFBFBD> <20> |
<20><><EFBFBD><EFBFBD><EFBFBD>ij <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> --------------------
| <20> <20> |
| <20><><EFBFBD> |
| |
|----1 1/4"---|
Figure # 3 COAX Connection
<20> <20> Maintain exact distance between the two
<20> <20> antenna's at top and bottom (points a & b)
<20> <20>a<<3C><><EFBFBD>>b<> <20>
<20> <20> <20> <20>
Shield <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>><3E><>Ŀ<EFBFBD><C4BF><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ĵ<<3C><> Center conductor
<20> <20><><EFBFBD> <20> <20>
Apply "super glue" <20> <20><><EFBFBD> <20> <20> Apply several coats of epoxy to
between antenna and <20> <20><><EFBFBD> <20> <20> center conductor for stabiliy.
coax to keep it in <20> <20><><EFBFBD> <20> <20> Apply 1 coat of epoxy to all
place while epoxy <20> <20><><EFBFBD> <20> <20> screws and nut's as well as
dries. <20> <20><><EFBFBD> <20> <20> the coax to the LONG inner side
<20> <20><><EFBFBD> <20> <20> antenna.
<20> <20><><EFBFBD> <20> <20>
ڳ <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ij <20><>
<20><>O<EFBFBD><4F><EFBFBD> <20>O<EFBFBD><4F>
<20><><EFBFBD>ٳ<EFBFBD><D9B3><EFBFBD><EFBFBD>Ŀ<EFBFBD><C4BF>ٳ
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٳ O<> <20>
Coax <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD> <20>
<20><><EFBFBD><EFBFBD><EFBFBD>ij <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
<20> <20>
<20><><EFBFBD>
Figure # 4 BASE<53>MOUNT
Bottom view
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ŀ ----
<20> <20> |
<20> <20> |
7/8" hole recessed <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ŀ <20> |
1/16". -------------<2D>-------><3E> ڿ <20> <20>
3/8" hole drilled---<2D>--------<2D>-><3E><> <20> <20> 4"
completely thru <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20>
plywood. <20> <20> |
<20> <20> |
<20> <20> |
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> ----
| |
| |
|---------- 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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