The Black Widow - A Portable 15 Meter Beam - KG4JJH
The Black Widow - A Portable 15 Meter Beam - KG4JJH The Black Widow - A Portable 15 Meter Beam - KG4JJH
tor on the hub, through the hub, andthrough an “L” made of CPVC pipe. Thehorizontal pipe length is 31.5″, and thevertical length is 24″. These lengths weredetermined with the antenna wires installedand the terminal block floatingfrom its vertical support. To account forconstruction differences, cut the pipepieces slightly long and trim them insmall increments.Connect the coax to the SO-239 connectorfirst, then feed the coax throughthe hub, the drop ear elbow, the horizontalpipe, the 90° elbow, the vertical pipe,and out of a hole drilled in the pipe justabove where the terminal block will bemounted.Cut two terminals free from the strip.Clamp the driven element’s feed pointwire ends into each side of the terminalblock. Then loop the wire around theopen hooks at the corners using the permanentmarker lines as an aid. Attach thewires to the insulators. Dry fit all pipepieces until the terminal strip can bemounted to the lower end of the verticalpipe such that the driven element isstraight and parallel to the reflector. Attachthe two-terminal block with a smallsheet metal screw. Figure 5 shows themounted terminal strip.Strip the coax and attach its shield andcenter conductor to the terminal strip.When complete, check all wire dimensionswith a measuring tape and makeadjustments as necessary within an accuracyof 1 /8″. Remark the position of thescrew-eye mounting loops, if necessary.Align and glue the CPVC parts. (If youprefer not to glue the CPVC, leaveenough slack in the coax to allow removalof the pipe and terminal block assembly,and attach the pipes and couplings withscrews.) Paint the feed line support tomatch the hub.(A)Figure 7––Theerectedantenna. In theair, the antennaresembles ablack spiderwith its legshanging down.Mast and SupportThe painter pole can be supported ina variety of ways but should be guyed atthree points. I fashioned my support from2 × 4s to fit my trailer hitch and used thepickup truck tie points and a ground stakeas guying anchors. The bed of the truckalso serves as a convenient platform toraise and lower the mast. A PVC coupling,with holes drilled for twine guylines slips over the pole. Be sure to drilland install a small screw into both endsof the plastic handle socket that connectsthe painter pole to the hub. This pins theantenna and prevents it from turning onthe mast.The finished Black Widow weighs lessthan 5 pounds and is stable at a height of15 feet in windy conditions. On a calmday it could be extended to the full 234 May 2003(B)Figure 8— (A) Broken down into its major components—spreaders, hub, feed linesupport and wire elements, the Black Widow is ready for transport. The partiallyassembled antenna (B).
feet, improving the gain and lowering theangle of radiation. Figure 6 is a view ofthe antenna support bracket and Figure 7shows the erected antenna.SetupFigure 8A shows the Black Widowready for assembly. Remove the rubberstoppers from the ends of the fishingpoles and extend them to their full length.Screw all four fishing poles into the hub.With the assembly upside down on theground, attach the driven element wiresto the feed point and wind the wires oneloop around the screw hooks at the markson the wire. As you progress, the fishingpoles will begin to flex upward. Place thePVC pipe coupling with attached guywires (nylon twine) over the top of thepainter pole. Pick up the antenna, flip itover and screw the painter pole onto themast. Secure the antenna by inserting ascrew into the socket on both ends.Connect a feed line to the SO-239 andsecure it to the mast with Velcro or electricaltape. To help suppress RF currentson the outside of the coax shield, windfive turns of coax in a 6 inch coil nearthe antenna.Place the antenna and painter polemast into a suitable support. To preventthe painter pole from bending, raise themiddle section first and adjust the guywires as needed. Lower the middle sectionand raise and tighten the top section.Now raise the middle section again andtighten. Clothesline tighteners were usedon all guy wires to allow adjustment withouthaving to re-tie the twine.ResultsThe antenna was designed for PSK useat 21.070 MHz, but tests conducted withan MFJ antenna analyzer at heights of 15and 23 feet reveal a fairly flat responseof 1.2:1 to 1.3:1 across the entire 15-meter band. The EZNEC models predictedthe antenna to have a gain of 9 dBiat the 15 foot level and 10.45 dBi at the23 foot level. Likewise, the predictedSWR is 1.11:1 at 21.1 MHz.Upon completion, I wanted to see ifthe Black Widow would perform as I hadhoped. Tropical storm Isadore had justpassed through our area, so it was clearbut very windy. With an eye out for thewind, I mounted the antenna on thepainter pole at a height of only 15 feet.A good test for any antenna is to seehow well it performs at QRP power levels.With 5 W from my FT-817, my firstPSK contact was a station in San Diego,who gave me a signal report of 579. Notbad, considering that distance from myQTH in Tennessee is 1900 miles. Next, Iswung the beam toward Europe and contacteda station in the UK who gave mean RST of 589 and an uninterrupted QSOfor about 15 minutes. Wow, I was gettingexcited––that’s over 4000 miles!With the assistance of my brother(NG4T), further SSB/CW tests were conductedusing his TS-2000 at power levelsup to 100 W with great results. TheBlack Widow is easy to build, transportand set up. Figure 8A shows the antennaready for transport and Figure 8B showsit partially assembled. It will outperformmany portable 15 meter antennas. Goodluck and have fun!Notes1www.cebik.com/moxpage.html.2www.qsl.net/ac6la/moxgen.html.3www.eznec.com.Allen Baker, KG4JJH, received his license inSeptember 2000, after a lifelong dream ofbecoming a ham. He holds a BS in IndustrialEngineering from Tennessee TechnologicalUniversity and worked as an instrument andcontrols engineer with the Department of Energyin Oak Ridge, Tennessee. Allen is activeon the digital modes (10 through 40 meters)and loves to experiment with antenna designs.He can be reached at 211 BrochardtBlvd, Knoxville, TN 37922; awbaker@charter.net.May 2003 5
- Page 1 and 2: By Allen Baker, KG4JJHThe BlackWido
- Page 3: Figure 4--One of the two insulators
feet, improving the gain and lowering theangle of radiation. Figure 6 is a view ofthe antenna support bracket and Figure 7shows the erected antenna.SetupFigure 8A shows the <strong>Black</strong> <strong>Widow</strong>ready for assembly. Remove the rubberstoppers from the ends of the fishingpoles and extend them to their full length.Screw all four fishing poles into the hub.With the assembly upside down on theground, attach the driven element wiresto the feed point and wind the wires oneloop around the screw hooks at the markson the wire. As you progress, the fishingpoles will begin to flex upward. Place thePVC pipe coupling with attached guywires (nylon twine) over the top of thepainter pole. Pick up the antenna, flip itover and screw the painter pole onto themast. Secure the antenna by inserting ascrew into the socket on both ends.Connect a feed line to the SO-239 andsecure it to the mast with Velcro or electricaltape. To help suppress RF currentson the outside of the coax shield, windfive turns of coax in a 6 inch coil nearthe antenna.Place the antenna and painter polemast into a suitable support. To preventthe painter pole from bending, raise themiddle section first and adjust the guywires as needed. Lower the middle sectionand raise and tighten the top section.Now raise the middle section again andtighten. Clothesline tighteners were usedon all guy wires to allow adjustment withouthaving to re-tie the twine.Results<strong>The</strong> antenna was designed for PSK useat 21.070 MHz, but tests conducted withan MFJ antenna analyzer at heights of <strong>15</strong>and 23 feet reveal a fairly flat responseof 1.2:1 to 1.3:1 across the entire <strong>15</strong>-meter band. <strong>The</strong> EZNEC models predictedthe antenna to have a gain of 9 dBiat the <strong>15</strong> foot level and 10.45 dBi at the23 foot level. Likewise, the predictedSWR is 1.11:1 at 21.1 MHz.Upon completion, I wanted to see ifthe <strong>Black</strong> <strong>Widow</strong> would perform as I hadhoped. Tropical storm Isadore had justpassed through our area, so it was clearbut very windy. With an eye out for thewind, I mounted the antenna on thepainter pole at a height of only <strong>15</strong> feet.A good test for any antenna is to seehow well it performs at QRP power levels.With 5 W from my FT-817, my firstPSK contact was a station in San Diego,who gave me a signal report of 579. Notbad, considering that distance from myQTH in Tennessee is 1900 miles. Next, Iswung the beam toward Europe and contacteda station in the UK who gave mean RST of 589 and an uninterrupted QSOfor about <strong>15</strong> minutes. Wow, I was gettingexcited––that’s over 4000 miles!With the assistance of my brother(NG4T), further SSB/CW tests were conductedusing his TS-2000 at power levelsup to 100 W with great results. <strong>The</strong><strong>Black</strong> <strong>Widow</strong> is easy to build, transportand set up. Figure 8A shows the antennaready for transport and Figure 8B showsit partially assembled. It will outperformmany portable <strong>15</strong> meter antennas. Goodluck and have fun!Notes1www.cebik.com/moxpage.html.2www.qsl.net/ac6la/moxgen.html.3www.eznec.com.Allen Baker, <strong>KG4JJH</strong>, received his license inSeptember 2000, after a lifelong dream ofbecoming a ham. He holds a BS in IndustrialEngineering from Tennessee TechnologicalUniversity and worked as an instrument andcontrols engineer with the Department of Energyin Oak Ridge, Tennessee. Allen is activeon the digital modes (10 through 40 meters)and loves to experiment with antenna designs.He can be reached at 211 BrochardtBlvd, Knoxville, TN 37922; awbaker@charter.net.May 2003 5
Change language