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 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ------------------ ³x³ ³x³ < -- File off chrome plating | ³ ³ ³ ³ at two points marked with | ³ ³ ³ ³ "x" completely around | ³ ³ ³ ³ antenna's - about 1/4" | ³ ³ ³ ³ width. 2 1/2 " ³ ³ ³ ³ | ³ ³ ³ ³ | ³ ³ ³ ³ | ³ ³ ³ ³ | ³ ³ ³ ³ | 7/64" hole -->³O³ ³O³ <-- 7/64" hole ----------------- ÀÄÙ ÀÄÙ Figure # 2 ANTENNAÿBRACKET ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ Thumb ³ ³ ³ ³ screw ³ ³ ³ ³ ³ ³ ³ Ú³ ³ÄÄÄÅÄÄij ³¿ -------------------- ÚÄÄÄÄÄÄÄ>³³O³ ³ ³O³³<ÄÄÄÄ¿ | 7/64" hole ³ ³ÀÄÙÚÄÄÄÄÄ¿ÀÄÙ³ ³ 7/64" hole 1/2" ÀÄÄÄÄÄÄÄijÄÄ>³O O³<ÄijÄÄÄÄÄÙ | ³ ÀÄ¿ ÚÄÙ ³ | ÀÄÄÄÄij ³ÄÄÄÄÄÙ -------------------- | ³ ³ | | ÀÄÙ | | | |----1 1/4"---| Figure # 3 COAX Connection ³ ³ Maintain exact distance between the two ³ ³ antenna's at top and bottom (points a & b) ³ ³a<ÄÄÄ>b³ ³ ³ ³ ³ ³ Shield ÄÄÄÄÄÄÄÄ>³ÄÄ¿ÚÄÄÄÄÄÄÄ´<ÄÄ Center conductor ³ ³³³ ³ ³ Apply "super glue" ³ ³³³ ³ ³ Apply several coats of epoxy to between antenna and ³ ³³³ ³ ³ center conductor for stabiliy. coax to keep it in ³ ³³³ ³ ³ Apply 1 coat of epoxy to all place while epoxy ³ ³³³ ³ ³ screws and nut's as well as dries. ³ ³³³ ³ ³ the coax to the LONG inner side ³ ³³³ ³ ³ antenna. ³ ³³³ ³ ³ Ú³ ³³³ÄÄÄÄij ³¿ ³³O³³³ ³O³³ ³ÀÄÙ³³ÄÄÄÄ¿ÀÄÙ³ ÄÄÄÄÄÄÁÄÄÄÙ³ O³ ³ Coax ÄÄÄÄÄÄÄ> ÄÄÄÄÄÄÂÄÄÄÄÁ¿ ÚÄÙ ³ ÀÄÄÄÄij ³ÄÄÄÄÄÙ ³ ³ ÀÄÙ Figure # 4 BASEÿMOUNT Bottom view ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ---- ³ ³ | ³ ³ | 7/8" hole recessed ³ ÚÄÄÄÄÄÄ¿ ³ | 1/16". -------------³------->³ Ú¿ ³ ³ 3/8" hole drilled---³--------³->ÀÙ ³ ³ 4" completely thru ³ ÀÄÄÄÄÄÄÙ ³ plywood. ³ ³ | ³ ³ | ³ ³ | ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ---- | | | | |---------- 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!