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The MFJ-949C Versa Tuner II BY LEW MCCOY ' . WlICP
M F'" Enterprises ma nufacturers a rather extensive line of Transmatches. and I recently had the oppo rtunity to lest their model 949C, which is also designated the " Versa-Tuner 11. " I have probably designed , built . and wrote up more antenna tuners (Tra nsmatche s) than anyone arou nd today. so I had a real interest in the MFJ unit.
The ci rcuit of the antenna system mat ching portio n, fig. 1, shows us tnet the 949 is what is now considered standard for those Transmatch circuits using a tapped inductor. Both Input and output capacitors are 208 pF variables used with a tappedfswitched Inductor L t . However , the 949 is much more than just the matching portion of the circuit. Also included is a POWER/SWR bridge for tuning up. Additionally, there is a complete swi tching circui t whereby two different coaxial-fed systems can be switched or a bypass position is ava ilable for removing the Transmatch from the antenna system. Or, if de sired, a single-wire or balanced-line feed can be used and matched. A bonus is a 300 watt, 50 ohm dummy load that can be switched in to provide a perfect tune-up or testing loa d fo r the transmitter . The meter used for POWERISWR is the dual needle type . One needle indic ates reflected power and the other, forward power. I had used such an indicator some years ago and liked the system then, just as I do now with the Versa Tuner . Essentially two meters in one , the indications are easy to follow, and tune-up and adjustment ofthe949 becomes routine. The meter Is calibrated with three scalesforward power (up to 300 watts), reflected power (SO watts), and SWR. There are two power ranges, 30 watts or 300 watts, available by means of a panel switch .
At the upper left in this rear view are the two variable capacitors and the tapped inductor. At the right~and side is the noninductive dummy load resistor.
easy to tailor such antennas to come into the "perfect " matching range. I use a double-extended , 80 meter Zepp for my wire antenna, wi th open-wire feeders. This ante nna syste m, when used on all bands, will present some rat her extreme matching situations on some bands. I found that w ith the 949 I could obtain 1.5 to 1 or better on all frequenc ies . One
th ing about such a system-the load will always be "relatively" high impedance, so it isn 't always the best test for a tuner . Physically short verticals for 160,80, and 40 can present ve ry low reactive impedance. Sometimes, assuming the vertical is very short , radi at ion resistance becomes a fraction of an ohm . Such loads can be the real test for a fixed (tapped) In-
As MFJ points out, the 949, using a tapped inductor, will match most antenna systems to a perfect match. There are some antenna loads that fall outside of the range of the system , but it is usually
-Technical Editor, CD, 200 Idaho St., Silver City, NM 8806 1 44
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This photo shows the front-panel controls. The SWR/Power meter uses a dual needle type meter, at the left. SayYouSawltlnCQ
Fig. 1- This is the circuit of the MFJ 949C• The le ft-hand portion of the c troun makes up the power bridge and SWR detectors . At the right-hand side is the actual tuning network.
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ductor tuner. (Ro lle r inductors make suc h match ing relatively easy .) In most cases , the 949 handled these short antennas very well . The maximum power rating the tuner will handle is 300 watts. M FJ's inst ructio n manual, which by the way is excellent , carefu lly points out that the 300 watt le vel should not be used for more than two m in-
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utes, key down . In other words, the 300 watt rating is for CW or sing le-sideband , not RTTY .I tested the unit on RTTY at 150 watts and had no problems. A lso, as pointed out i n the manua l, th is unit, or for that matter any Transmatch, must be adjusted for a match using the lowest possible power, After a match is achieved, then , and only then, should power be
brought up to normal operating levels. Under unmatched conditions some very, very high RF vo ltages can be developed, causing arcing of components . The 949Cmeasures 10 V. inc hes wide , 3 V. inches high, and 7 inc hes deep. It lists for $149 .95 and is available from MFJ Enterprise s, tnc ., Box 494 , Mississippi State, MS 39762.
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