The NJQRP Squirt

1 From April 2001 QST ARRLAtBy Joe Everhart, N2 CXone time, 80 meters was one ofthe more highly populated ama-teur bands. Lately, it has becomesignificantly less popular because muchDXing has moved to the higher frequen-cies and many suburban lot sizes are toosmall to accommodate a full 130-foot, /2 antenna for the band. That s unfortu-nate, because 80 meters has lots of po-tential as a local-communicationband even at QRP levels. The recentlypublished Warbler PSK31 transceiver canserve as a great facilitator for close-inQRP communication without much What s really needed to comple-ment the Warbler for this purpose is aneffective antenna that fits on a small sub-urban plot. Because PSK31 (which theWarbler uses) is reasonably effectiveeven with weak signals, we can trade offsome antenna efficiency for s a Ham to Do?

2 I investigated a number of antennapossibilities to come up with a practicalsolution. One intriguing candidate is themagnetic loop. Plenty of design informa-tion for this antenna is presented in TheARRL antenna Book and at a number ofWeb , 3 To obtain high efficiency,however, the loop must be 10 feet or morein diameter and built from 1/2-inch orlarger-diameter copper pipe. The loopneeds a very low-loss tuning capacitorand a means of carefully tuning it becauseof its inherently narrow bandwidth. An-other configuration, the DCTL, may be asolution, but it s likely not very old standby antenna I considered isthe random-length wire worked againstground. If it is at least /4 long (a Marconiantenna) or longer, it can be reasonablyefficient. Shorter lengths are likely to beseveral S units down in performance andalmost any length end-fed wire needs asignificant ground system to be course, you may not need much of aground with a /2 end-fed wire, but it s as1 Notes appear on page NJQRP SquirtThis reduced-size 80-meter antenna is designed for small build-ing lots and portable use.

3 It s a fine companion for the WarblerPSK31 1 General construction of the 80-meter Squirt 2 An assembled Squirt ready as a center-fed antennas don t occupy muchground space, but suffer the same lowefficiency as the end-fed wire if they arepractical in the easiest antenna to usewith good, predictable performance is thehorizontal center-fed dipole. Unfortu-nately, as mentioned earlier, the usual80-meter /2 dipole is too large for manylots. But all is not lost! The dipole can bereduced to about a quarter wavelengthwithout much sacrifice in operation (seethe sidebar, Trade-Offs ). Furthermore,if the dipole s center is elevated and theends lowered resulting in an invertedV it takes up even less room. This ar-ticle describes just such a dipole: theNJQRP for VictoryYou can think of the Squirt as a40-meter, /2 inverted-V dipole beingused on 80meters.

4 Figure 1 is an overallsketch of the antenna ; Figure 2 is aphotograph of a completed Squirt priorto erection. The Squirt has two legs about34 feet long separated by 90 with a feedline running from the center. When in-stalled, the center of the Squirt should beat least 20feet high, with the dipole endstied off no lower than seven feet aboveground. This low antenna height empha-sizes high-angle NVIS (Near Vertical-Incidence Skyware) propagation that sideal for 80-meter contacts ranging fromnext door out to 150 or 200 miles. AndFrom April 2001 QST ARRL that s where 80 meters shines! With theSquirt s center at 30 feet and its ends atseven feet, the antenna s ground footprintis only about 50 feet nice feature of a /2 center-feddipole is that its center impedance is agood match for 50- or 75- coax cable(and purists usually use a balun).

5 Ah! Butthe Squirt is only /4 long on 80 meters,so it isn t resonant! Its feedpoint imped-Figure 3 Hole sizes and locations for the various PC-board pieces. See Note is resistively low and reactivelyhigh. This means that feeding the antennawith coax cable would create a high SWRcausing significant feed-line loss. To cir-cumvent this, we can feed the antennawith a low-loss feed line and use an an-tenna tuner in the shack to match the an-tenna system to common 50- coaxcable. I ll have more to say about thetuner use 300- TV flat ribbon line for thefeed line. Although a better low-loss so-lution is to use open-wire line, that stuffis not as easy to bring into the house as isTV ribbon. Using TV ribbon sacrifices alittle transmitted signal for increased con-venience and availability.

6 If you feel bet-ter using open-wire line, go for it!Using Available MaterialsIt s always fun to see what you can dowith junkbox stuff, and this antenna isone place to do it. See the Parts List for information on materials and instance, the end and center insula-tors (see Figure 1) are made of 1/16-inch-thick scraps of glass-epoxy PC board. Forthe antenna elements, I use #20 or #22insulated hookup wire. Although this wiresize isn t recommended for use with fixedantennas, I find it entirely adequate formy Squirt . Because it s installed as an in-verted V antenna , the center insulatorsupports most of the antenna s weightmaking the light-gauge wire all that sneeded. The small-diameter wire has sur-vived quite well for several years atN2CX. This is not to say, of course, thatsomething stronger like #14 or #12 elec-trical house wire couldn t serve as 300- TV ribbon can be pur-chased at many outlets includingRadioShack and local hardware again, if you want to use heavier-duty feed line, do so.

7 The only proviso isthat you may then have to trim the feederlength to be within tuning range of theSquirt s antenna End InsulatorsI used 1/2 11/2-inch pieces of 1/16-inchPC board for the Squirt s two end insula-tors. As with everything else with theSquirt, these dimensions are not sacred;tailor them as you wish. If you use PCboard for the end insulators, you have toremove the copper foil. This is easy todo once you ve gotten the knack. Prac-tice on some scraps before tackling thefinal product. The easiest way to removethe foil without etching it is to peel it offusing a sharp hobby knife and needle-nose pliers. Carefully lift an edge of thefoil at a corner of the board, grasp thefoil with the pliers and slowly peel it should become an expert at this in10 or 15 minutes.

8 Drill 1/8-inch-diameterholes at each end of each insulator for theelement wires and Feed-Line ConnectorThe tuner end of the feed line is ter-minated in a special connector. Becausethe TV-ribbon conductors aren t strong,they ll eventually suffer wear and April 2001 QST ARRLT rade-OffsOne of the unfortunate consequences of shrinking an antenna s size is that itselectrical efficiency is reduced as well. A full-size dipole is resonant with a feedpointimpedance that matches common low-impedance coax quite well. This means thatmost transmitter power reaches the antenna minus only 1 dB or so feed-line , when the antenna is shortened, it is no longer resonant. A NEC-4 modelfor the Squirt shows that its center impedance on 80 meters is only about 10 resistive, but also about 1 k capacitive. This is a horrendous mismatch to 50- cable, and feed-line loss increases dramatically with high SWR.

9 The Squirt uses300- TV ribbon for the feed line with an inherently lower loss than coax. This lossis much less than if coax were used, but it s still appreciable. Calculated loss with300- transmitting feed line is about dB (loss figures are hard to come up withfor receiving TV ribbon) so the feed line used doubtless has more than this sounds discouraging, it s not fatal. You have to balance losing anS unit or so of signal against not operating at all! Consider that the Squirt , even withits reduced efficiency, is still better than most mobile antennas on 40 and 80 for local communication (a low-dipole s forte), using PSK31 and the Squirt is you don t already have an antenna , the Squirt s a good choice to get your feetwet when using PSK 31. Once you get hooked, you ll probably want a better you have the room, put up a full-size dipole; you ll see the improvement right you can t do that, use a lower-loss feeder on the Squirt , such as good-quality openwire.

10 Joe Everhart, N2 CXFigure 4 The pad sideof the home-made 5 Here the feed-line-to-tunerconnector is shown attached to the bind-ing posts of the Squirt antenna connector provides needed mechani-cal strength and a means of easily attach-ing the feed line to the tuner. In additionto some PC-board material, you ll needfour or five inches of #18 to #12 solid,bare wire. Refer to Figure 3 and the ac-companying photographs in Figures 4and 5 for the following a 11/8 13/4-inch piece of single-sided PC board and score the foil about1/2inch from one end; remove the11/4-inch piece of foil. Now score the re-maining foil so you can remove a 1/8-inch-wide strip at the center of the board, leav-ing two rectangular pads as shown inFigures 3B and 4. Drill two 1/16-inch-diameter holes in the copper pads spac-ing the holes about 3/4-inch apart.