May 2000 QST

WORKBENCHPROJECTS AND INFORMATION FOR THE ACTIVE AMATEURThe Doctor is INQGeorge, KD4KYM, asks, “I’m uncertain about how Ishould attach a 450-Ω ladder transmission line to myradio. I have SO-239 coax connectors on my Kenwood TS-520transceiver. Can I assume that it is simply a matter of solderingone side of the ladder line to the center conductor of aPL-259 and the other to the outer conductor? I want to use theladder line to feed a multiband 80-10 meter dipole antenna.”AYour TS-520 was designed for 50-Ω unbalanced coaxialcable. Your ladder line is 450-Ω balanced, so there is moreto deal with than just the physical differences. If you were goingto use the ladder line on just a couple of bands, you might be ableto get away with feeding the ladder line to a balun (a balanced-tounbalancefeed line transformer) with an appropriate impedanceratio (4:1, for instance), then using coax between the balun andyour radio. But since you’re aiming for broad, multiband coverage,I’d recommend an antenna tuner.Most antenna tuners are designed with built-in baluns to handlethe impedance transformation. There are usually three posts inthe back of a tuner—two for ladder-line and one for random wireantennas. There may be a jumper between the random wire postand one of the ladder-line posts. Make sure the jumper is removed—itis only used for a single random-length wire.If your tuner does not have provisions for ladder-line, you canconnect it as you say, by soldering the ladder line to a PL-259. Itmay work, but not as well as using a balun. Of course, you couldalways install an external balun in the line between the ladderlineand the antenna tuner (see Figure 1), although we don’t recommendthat you run high power with such a setup.Figure 1—If you own an antenna tuner that does not include an internal balun, you can use an external balun. Just keep thecoaxial connection between the balun and the tuner as short as possible.QGary, KD4SRX, asks, “I read the product reviews inQST, talk with other hams and radio dealers, and I’m stillvery much confused about handhelds (H-Ts). I’m not sure whatmodel would suit my needs. To be more specific, I like workingvarious ham events, as well as taking my handheld on Amtraktrain trips along the Northeast Corridor. With all these variousmodels to choose from, which features are the most important?”AI’d suggest that you look for an H-T with a large battery pack(you may have to purchase this separately). Choose a packthat has enough capacity to last through a daylong hamfest orpublic-service event. I would suggest looking for one that has atleast 600-m/Ah capacity.Also, although 5W output is not a must, having at least 2 1 /2 to3 W helps when trying to work someone (via simplex) who is onthe other side of the hamfest grounds (for an outdoor hamfest).Higher output power will also be helpful when attempting to workstations from a moving train. Most modern handhelds will receivethe 160-161 MHz Amtrak frequencies in the Northeast Corridor,but check the specs to be sure.Concerning battery life, consult the QST Product Reviews andrefer to the power requirements section. This will tell you themaximum receive and transmit current drawn for each handheldunder consideration.Ease of programming is another thing to consider, but there isa mitigating factor. If your H-T has a lot of features that you won’tuse, it doesn’t matter if you can’t remember (or figure out) howto program them. I prefer H-Ts with the most frequently used46 May 2000functions marked on the buttons (like switching between memoryand VFO mode, setting PL tones, etc.). Failing that, you can makeup a small (2-inch square) “cheat sheet” with the most importantfunctions written on it.Unless you plan on carrying the manual with you everywhere,direct keypad frequency entry is practically a must. Also convenientis automatic repeater offset, although that is more of a luxurythan a necessity (if “-” doesn’t bring up the repeater, just switchto “+” —assuming you don’t need to consult the manual to rememberhow).Don’t forget audio quality. You want to be able to understandwhat is being said, even when you are in a noisy area. If a particularradio’s audio is poor, the Product Review will mention it.Most H-Ts are pretty rugged. You don’t have to treat them asyou would an expensive camera, but reasonable care is required(a 3-foot drop onto a hard surface is survivable if it only happensonce in a great while).QBill, N3SNU, asks, “The display malfunction on my ADI-146 is definitely temperature-dependent. During summer,and to a lesser extent during spring and fall, all thesegments of the LCD display activate so it is impossible to tellwhat frequency the radio is on, or any other displayed parameters.The radio apparently still works fine. Transmitting,especially on high power, causes heat to build up faster and thedisplay to go haywire sooner, but in hot weather just havingthe radio on receive during a long drive will eventually bring