.. : ..

o------Loop of nylon line Dual-Band (to hang ) VHF/UHF

Standard Flat Twinlead 300 ohm Twinlead J-Pole Antenna

By James A. Williams Cut out wire and insulation 54inches 1/4" notch ant to get more range out of that handhcld transceiver that just can ·t quite make that distant re­ Wpeater all your friends brag about? Or how about an emergency antenna that you can eas ily put up and use when a tornado or other natural d isaster takes down your main an­ tenna, or lightning causes you to have to 15.25" inches disconnect that beam you have 60 feet in the air'l Or do you li ve in an apartment or deed restricted subdi vision that will not let you have outside antennas'> If you have 30 minutes to Cut out small notch, spare. you can bui ld a Dual-Band remove only insulation Cut out small notch, VHF/UHF J-Pole antenna that DO NOT NI CK WIRES remove only insulation is guaranteed to get you on the Solder coax center conductor DO NOT NICK WIRES air quickly, outperform the rub- Solder coax braid (shield) berduck antenna that came with yourhandheld. J_ and solve all the above problems and then ~ .25" inches some. It will serve not only as an emergency antenna, but as a portable antenna system for anyone needing an easy-to-set-up antenna. ~ Twist wires together and solder such as travelers who want to monitor or operate from their hote l room. The low profile antenna can be set up and taken down quickly. For this article the we will concentrate on length radiator and a 1/4 wave length match­ and it stores in the space of an eyeglass case. the most popul ar bands in thi s country: the 2 ing stub that operates like an end-fed halfwavc It can be hung in a corne r of a room. attic or meter band ( 144 M Hz to 148 MHz) and the 70 antenna. If built to exact specs listed. there is other out of the way location for a mon: cm band (440 M Hz to450 M Hz). I have found no tuning needed for this antenna. Just build it permanent installation, or can be put up and the antenna to have a voltage and USC it. taken down when needed. ratio (VSWR) of less than I :5: I across the The Dual-Band Twinlead J-Polc antenna The J-Polc antenna has been used by ham entire 2-me ter band, and less than I: 7: I across is made from standard flat 300 ohm twin lead operators around the world for years. the 70-cm band. As a scanner antenna (non­ TV antenna wire. avai lable from most hard­ It· s one of the first antennas that most new transmit) it is usable from 30 MHz through the ware and electronic stores. Most of us oldtimcrs harm hear about and wish to acquire. Several gigahertz bands. wi ll remember this wire as the twinlead used commercial antenna manufacturers make and I will not get into the theory or math in­ to connect a TV to the roof-mounted antenna sell this type of antenna in the price range of volved in the construc ti on of this antenna. that almost all homes in th is country dis­ from $ 15 to $25 dollars each; you can make it other than to state that it is a vertically polar­ played before the advent of cable TV. You can for $3 or $4 dollars. ized antenna with two c lements: a 3/4 wave- use an old pi ece of twinlcad you or a friend

20 MONITORING TIMES April 1998 may have lying around or huy a new piece 6 i nchcs above and below the mark. be ing care­ shri nk tubing at the notch you cu t out to make foot long. fu l not to nick the wire. Repeat on the other the ground side (stub) of the antenna. side of the twin lead. Punch a hole at the top of the an tenna at the You will need the following: M easure exactly 15.25 inches from the one center and tie a loop of nylon line (fishing) or of the notches you have just cut and remove a another nonconducting line to hang the an­ 6 feet of nat 300 ohm twin lead .25 inch notch from this point: remove both tenna from the ceiling, tree limb or other 6 feet or more of RG-58 coax the insulation and the wire. This is the ground location. Install your choice ofco nnector (PL- PL-259 or BNC connector (your choice) side ( 1/4 wave stub). The other uncut side is 259. BNC. etc.) to the coax and use. You will Soldering Iron and Solder the radiator side (3/4 wave) of the antenna. find that the antenna will have a gain of 3 to 4 Wire Cutters, strippers or knife Using a piece of RG -58 coax at least 6 fee t dB. Plastic electrical tape or heat shrink tubing long. carefully remove .75 inches of insula­ When using the antenna try to keep it away tion from the coax to ex pose the braid. Sepa­ from metallic objects such as electrical wiring I Building the Antenna rate the braid from the center conductor and and plumbing. It is possible to detune the twist together. Remove the insulation from antenna i f it is close to such objects. For a Begin hy carefully removing 0.75 inch of the center conductor. Connect the braid from permanent outdoor installation. mount the J­ insulation from one end of the twin lead. being the coax to the ground side (stub) of the Pole inside a piece of PVC pipe capped at both carefu l that you also do not cut the wires. Once twin lead and the center conductor to the long ends. Drill a hole in the bottom cap for the the wire has been stripped. twist the pair of side (radiator) of the twinlcad. Try to connect coax to pass th rough and seal around the coax wires together and solder. This is the bottom the coax so that it lays in the center of the with a good waterproof scaler. M ount on top of the antenna. twinlead. Solder the coax braid and center of your mast or tower. Cut the twinlead to 54 inches exactly from conductor to the twinlead. By bui lding several of these low cost. easy top to bottom. Double check the length: it Use elec trical tape or heat shrink tubing to to construct antennas you can keep one handy needs to bt: exact. sec ure the coax to the twinlcad. This will help at all times-such as in your car glove com­ Measure 1.25 inches up from the bollom of take the stress off the solder points and make partment. briefcase or back pocket- and en­ the antenna and mark the in~ulation. From th is the j oint waterproof. A lso tape or use heat joy the improved performance of this antenna mark. carefully remove the insulation for .25 anytime.

Listening Post State-of-the-art scanning software. Features: Standard Flat • Easy to use Explorer-type interface 300 ohn Twinlead • Full featured scheduler • Advanced reporting engine • Audio Processing Plug-In support for ACARS, inversion, etc. • Digital audio logging to database • Full 32-bit multitasking for high performance scanning and reporting Solder coax Solder coax braid Scanner Support: Opto OS456, 535, ICOM 7000, ICOM center conductor--­ - (shield) to wire 7100, ICOM 8500, ICOM 9000, AOR to wire 3000, AOR 8000 and WinRadio Includes frequency database • FCC database • Aviation database • Fed frequencies • Cut 'n paste or drag & drop into LP • Sort, search and proximity search All for $99.95 on CD / $79.95 on diskettes w/o database Tape or Heat Shrink Tubing For more info, see www.lpcom.com Coax to Twinlead. Try to Coax LP Communications, Inc. center coax on twinlead 51 14 Balcones Woods Dr. Ste. 307- 305, Austin, TX 78759 as shown. Phone(512)260-3478

April 1998 MONITORING TIMES 21