-- o ICOM

More documents

Recommendations

Info

Number 12 on your Feedbackeard 73 Review by Bill Clarke WA4BLC The MFJ Differential-T Antenna Tuner MFJ Enterprises, Inc . PO Box 494 Miss. State, MS 39762 601-323-5869 800-647-1800 Price Class: $240 A simpler, surer tuner. Over the years, various configurations have appeared on the market and in magazine construction articles. Each was alleged to be an improvement over all the others. Some may have been, but the majority just plain worked, at least after a fashion. Antenna tuners can be thought of as variable transformers that compensate for di fferences between your antenna's actual RF impedan ce and the impedance you r transceiver would like to see at its coax connector. They are the great equalizers in the game of reducing the SWR seen at the rig . In manual tuners, the operator must make manual adjustments to controls on the antenna tuner for it to do its job. Generally, tuner adjustment consists of selecting an appropriate inductance from a multi-position switch and adjusting two variable capacitors until the SWR indication at the transmitter is at 1:1 (or as low as you can get it). SWR is indicated by a meter that must be switched between forward and reflected power to obtain comparative readings. New Version A few mo nths ago, MFJ introduced the Model 986 Differential-T Antenna Tu ner. It is a 3 kW unit, providing very simplified (only two controls) broadband t uning and incorporates all the AF output metering you'll usually ever need. This tuner uses a single differential va riable capacitor and a roller inductor in a 'r-Network circuit. The usual tuner configuration consists of two variable capacitors and a switch-selected inductor in a Pi-network. The first obvious improvement on this tuner is that there is one less variable control for the operator to adjust. Merely crank the variable inductor and turn the capacitor control until the SWA is maximally dipped. Photo B. Rear panel provides teeanne. ground, and 12 volt DC connectors. 42 73AmateurRadio . June,1989 A cross-needle SW R meter is built into the unit , giving si m u ltaneous readi ngs of forward and refl ected power. A novel inclu sion is a peak reading meter circuit for SSB power output. T his is a f eature many SSB operators want. Before now, that meant the purchase of a separate meter costing as much as $300. Features The Mod el 986 has: • Continuous 3 kW fro m 1.8 through 30 MHz. • A dual-range (200/2000 Watts) back-lighted cross-needle meter providing SWR, power, and peak reading functions. • A g-positicn ceramic switch allows serection between two coax feeds, a bal anced line, or a dummy position (which could be used for a bypassed antenna or dummy load). • An internal balu n lor balanced feedlines. • Small size (10.75" x 4.5 " x 15.0"). Inside the Model 986 Before operating the MFJ-986, I removed the covers. Inside I found a large roller inductor with 62 turns on it, with an attached beltdriven turns co unter. The capacitor is of high quality construction with adequate spacing for all legal ham output powe r (and then some). The antenna switch is ceramic and the balun is constructed 01 two st acked toroids wit h windings positioned in a manner thai should preclude any flash-over problems. Soldering and mechanical work shews itself well , with no obvious defects or poor quality workmanship noted. u•• The instructio n manual in cludes a small chart for preliminary settings lor each band. Using the recommended settings, I tuned my 75 meter loop for 3947 kHz. Tuning was done by turning th e roller inductor crank until the counter indicated 046. I then applied a little power and continued inductor adjustment until I located the lowest reflect ed power indication point. Afterwards I adjusted the capacitor for further reduction . I then fine tuned with Photo A. Front view ofthe MFJ·986 showing the two tuning controls, antenna selector switch, and the cross-needle meter. these two controls. Total time for the first tuning was nine seconds. I then logged the capacitor setting from its vernier sca le and the inductor setting from the inductor's counter. This information is good as a starting point when retuning the same antenna system for the sa me resonant frequency later on . I then tuned the same antenna lor each ham band. There were no problems and all settings were logged . Using the loop has presented a problem for my othertuneron 1Oand 15 meters, but the MFJ-986 tuned it with no problems. The last operational test was to reset the tuner for each band per my notes based on the previous settings. The unit proved to be very resetable, although some fine tweaking was needed on 75 and 160 meters. Varied Comments The turns counter is rel ative only, but it's completely accurate for logging and resetting. Havin g the built-in cross-needle forward/ reflected meter is a real advantage over other tuners. The peak reading meter is ideal for tnose of us attempting 10 run a full gallon. The antenna selector switch should be selfgrounding. As it's set up, feedlines not in use are not grounded. Due to the design 01 the differential-T circuit, it is possible to gel a low SWR at only one combination of the controls. No more worry about too m uch inductance. Highly Recommended Pricewlse, the unit is a bargain. Yo u get a cross-needle meier thai includes simultaneous forwardfreflected indications and selectable peak reading, an antenna selector switch, and a 3 kW tuner all in one box. Yet the unit sells for over $100 less than its nearest competition, which is the MFJ-989B. Do I recommend this tuner? Yes! It is economical, solid, and easy to use. DI
SAVE TIME and MONEY with THE HAZER Bring things down for safety and convenience. _____n ..."'__..""S)'S,..... _ '-_ OIlor"""""'.... HAl(II......._OJ'Sl_ r_ _ "P"ght Q" ' 101 '- $01"" 10
Page 2 and 3: With One YearWa K7SS , "01 all the
Page 4 and 5: Food for thought. OUf new Un iversa
Page 6 and 7: • Number 1 on yourFndbKken Welcom
Page 8 and 9: _______________________________1 Nu
Page 10 and 11: e! ACTUAL SIZE FRONT PANEL TM-621A/
Page 12 and 13: or a TS-140S HF transceiver with ge
Page 14 and 15: , Number 4 on your FeedbKk card Spr
Page 16 and 17: 73 Review by MichaelJ. Geier KBI UM
Page 18 and 19: - , - hy-gain antennas & towers Tri
Page 20 and 21: Continued from page 14 The priority
Page 22 and 23: : Number, on yourFMdback eard QRP C
Page 24 and 25: • zeroing the frequency of the VF
Page 26 and 27: em Table 2: Frequency Dependent Val
Page 28: Number7on YOtlr Feedback u rd The G
Page 31 and 32: to the PA, giving different power o
Page 33 and 34: THE U SPEt (KOW8,fi /DVP/ Pt:8 .J
Page 35 and 36: AMATEUR SOFTWARE FOR YOUAIBM PClXT/
Page 37 and 38: a large digital component. There ar
Page 39 and 40: Authorized Liquidator Now it's easy
Page 41 and 42: ~·,w~ . '" ._.,."" ........"."" 'N
Page 43: See You June 4th-HOSARC, Queens, NY
Page 47 and 48: The HF5B "Butterfly"'· A Compact 2
Page 49 and 50: Atlanta HamFestival July 8th & 9th
Page 51 and 52: onfinuedjromp.25 W inding a transfo
Page 53 and 54: , t.a r r r. " I , 6 A II"~ 6A II"
Page 55 and 56: tor. An RF gain control prevents ov
Page 57 and 58: Look at our Mf)B!LE flt1A.!:ll(" VH
Page 59 and 60: Hf Equipment br;ular SALE le-76S Xc
Page 61 and 62: ATV CONVERTERS • HF LINEAR AMPLIF
Page 63 and 64: RX eye. Up to 16 TX waveforms (32 o
Page 65 and 66: UNCLf WAl'Nf'S BOOITSUfLf · F....
Page 67 and 68: Numbef" 20 on your Feedback c.rd CW
Page 69 and 70: lV.1. problems? Low pass lV,1. filt
Page 71 and 72: No gain.No pain. Maintaining a mode
Page 73 and 74: and gels about + 5 dBm output on tr
Page 75 and 76: VISO SUPER PERFORMANCE BATTERIES SU
Page 77 and 78: SPECIALISTS IN FAST TURN P.C. BOARD
Page 79 and 80: KIT, ONLY $675 WIREO$975 VHFOR UHF
Page 81 and 82: INDUSTRIAL PRINTER SALE IDEAL FOR I
Page 83 and 84: Bilt Pasternak WA61TF 28197RobinAve
Page 85 and 86: World's Most Powerful CB and Amateu
Page 87 and 88: D X-ing, contests, pileups, traffic
Page 89 and 90: ter the war he really did "reme~ be
Page 91 and 92: Listings are frfJfJ ofcharge liS sp
Page 93 and 94: nets, as so many involved are sayin
Page 95 and 96:
tt f]IICOMI ICOM IC·7Bt New Oelu x
Page 97 and 98:
100 a SL CARDS S81 Shipped postpaid
Page 100:
• TH-75A WO 2m170cm Dual Band HT
show all

-- o ICOM

Create successful ePaper yourself

Delete template?

Save as template?