John Stewart
Shreveport, LA

Amateur Radio Station

The Z-Match Tuner

John Stewart, AA5KV
November 1, 2006

Many hams work the HF bands using a multi-band antenna fed with ladder line or some other “open wire feeder”. The old “McCoy dipole” is a good example. Lew McCoy argued1 that the simplest and perhaps most effective antenna was a random length “dipole” fed with ladder line or open wire. Provided the total length is 88 feet or longer, the antenna is reasonably efficient on 80 through 10 meters. The loop antenna is another example of a simple and highly versatile antenna. The typical loop is cut for a half wave at the lowest frequency of use. Formed into a rectangle, triangle or some other geometric shape, the loop can also be fed with open wire. Hams today are slowly recognizing that open-wire is amazingly efficient. Even with long lengths of feed line and high SWR conditions, power loss in open-wire is almost insignificant at HF frequencies. Simple and efficient…you can’t beat that!

But like everything else in life, “there’s no free ride”. First, we have the problem of routing open-wire to the shack. Unlike shielded coax, open-wire should be kept away from conductive objects as much as possible (exactly how far is debatable). For most of us, this is a formidable challenge. For others, it’s impossible and coax is the only alternative. Secondly, we have to connect the unbalanced output of our transceiver to the balanced feed line. Unless you’re fortunate enough to have a “balanced tuner”, you must make some accommodation to match the balanced and unbalanced conditions. Many hams interpose a balun between the antenna tuner (ATU or transmatch) and the antenna. Some commercially produced ATU’s designed to work with unbalanced line include an optional balun at the output. These tuners are easily recognized by terminals labeled “bal” or something else suggestive of a balanced condition. At about one-twenty-fifth the price of 7/8 inch hard-line, the extra effort to use open-wire is well worth it2.

I decided to try a McCoy “dipole” (a tuned doublet) after using a G5RV for many years. I ended up with 134 feet of wire fed with 300 ohm twin lead (slightly more lossy than 450 ohm ladder line but acceptable nonetheless). My ATU was a MFJ 901B, an inexpensive tuner that I purchased some years ago. The 901B is a good little tuner for the price. Although the 901B is a T-network, high-pass tuner designed for unbalanced line or coax, MFJ thoughtfully included a balun at the output of the tuner for use with balanced line. I was in business.

Baluns Work….Kinda

I happily used the balun inside the MFJ 901B for several months and all was well. The 901B tuned the doublet to 1:1 SWR on 80 through 10 meters. Tuning on 80 was a bit “touchy” but the match was made with several notches of inductor left to spare. The antenna seemed to work fairly well.

Around this time, I read a product review in QST Magazine of five, fairly high priced, high-power ATU’s. I was amazed at how widely they varied in efficiency3!! Most of the ATU’s were fairly efficient with a high impedance load, but efficiency fell off dramatically for low impedance loads. I wondered about the efficiency of my tuner and balun arrangement. I looked inside the 901B and saw two relatively small variable capacitors with tight plate spacing. I especially worried about the balun. The balun in the 901B looked puny to say the least and appeared to be made from high permeability ferrite material. From my reading, I gathered that a 4:1 balun did fairly well at a resistive load of around 200 ohms. But the impedance of a “tuned” doublet varies considerably over the HF bands4. Under high SWR conditions, a balun, especially those made from highly permeable materials like ferrite, tended to “saturate” and lose their broadband transformer properties. As a result, at least some of the RF is converted to heat (i.e., wasted) and in the worse case scenario, the balun could suffer a catastrophic mechanical breakdown under the large voltages associated with high SWR. Furthermore, a 4:1 balun at the output side of a tuner had a nasty habit of converting a low impedance load, to an even lower impedance load, making it less, rather than more efficient. This was exactly what led to the large inefficiencies in the ATU review described above. The solution was to use a truly balanced tuner, that is, one designed for balanced feed line, like the old E.F. Johnson Matchbox5.

The Z-match

I searched for a good, commercially produced balanced tuner. “Good” tuners, like those tested and found reasonably efficient in publications like QST Magazine, were pricey, to say the least. But after pricing the components, I understood why they were so costly. (Check a few websites for prices of “broadcast quality”, air-variable capacitors and roller inductors.) Another interesting observation is that a truly balanced, link-coupled antenna tuner is not commercially available at the present time5. At best, you can look for a used Johnson Matchbox on eBay. I have seen some with bids in the range of 250 to 450 dollars, and certainly that is an option. But another option is to build your own, like the one described in the Antenna Book (Chapter 25).

I read about the z-match tuner on several reflectors and I was mildly interested. I finally did a web search on “z match” and discovered an article by Charlie Lofgren, W6JJZ, entitled “The Z-Match: An Update”6. Charlie, it turns out, is the “dean” of the z-match tuner, having written several articles in various magazines, including two that appeared in the ARRL Antenna Compendium (vols 3 and 5). I read his web article with great interest, but it wasn’t until Phil Salas (AD5X) described his z-match tuner in the January 2003 issue of QST Magazine7 that I got seriously interested in building one. Phil’s tuner included a neat SWR indicator, which I didn’t need. My Jupiter’s had SWR metering. That reduced components and made the job even easier.

Several characteristics of the z-match project attracted my attention. First, it was simple. Without SWR metering, the tuner reduced to three basic components: two capacitors and a toroid. Second, “simple” meant relatively inexpensive. I liked that. Thirdly, there were only two components to tune, not three like most tuners. Fourth, measurements indicated that the z-match is relatively efficient and balanced to within one dB 6,8. But the Z-match tuner is NOT a truly balanced tuner. It’s best described as a “semi-balanced” tuner. It simulates an L network and remains balanced over a relatively large impedance range. But balance eventually degrades at higher frequencies, especially under high impedance loads8. Still, the z-match is probably the simplest and least expensive “balanced” tuner in existence.

I decided build a rough version of the W6JJZ z-match.


If you’re interested in building a Z match tuner, study the schematic provided by W6JJZ6. Note that both variable capacitors, C1 and C2, are not grounded, that is, they are “floating”. This has a tremendous impact on construction techniques for this tuner. Because the capacitors are “hot with RF”, you must isolate the bodies of the capacitors, as well as the shafts, from ground and from the person operating the tuner. I instinctively used a metal enclosure to build my prototype. In fact, I used a relatively inexpensive TenTec enclosure, because I’ve used them in the past with good success. But because the capacitors are “hot”, using a wooden enclosure makes more sense and those of you with good wood-working skills (not me) can come up with something functional and aesthetically pleasing. I mounted my capacitors on a Plexiglas base and brought the capacitor shafts through the front panel using rubber grommets for insulation. I felt comfortable with this arrangement, because I never run more than 100 watts. If you’re a “QRO kinda-guy” (and you know who you are), check eBay for a high-power Johnson Matchbox.

Speaking of capacitors

I had no good air-variable capacitors in my junk-box, so I search the Internet. I found an acceptable capacitor at Ocean State Electronics (www.oselectronics.com). It was a dual section air variable capacitor (BC13380), listed as 13 to 380 pf per section that could be used for both C1 and C2. The price was $22.95 and I needed two. I would only use this capacitor if you’re running 100 watts or less. If you’re likely to push the power limit, get a more substantial capacitor, i.e. one with larger plate spacing. See below for additional advice on capacitor selection.

The Toroid

Winding the toroid is a "piece of cake", even if you’ve never done one before. I bought my toroid (T-200-6) from Amidon. Use the powdered iron toroid made from #6 material (usually colored yellow) as specified by W6JJZ. I’ve seen other z-match builders use a #2 material (usually colored red). I’m not sure it makes a difference, but Charlie claims it does. If you have a #2 toroid laying around, use it, but you’ll have to reduce the number of turns. See Charlie’s article or, if you’re interested, I’ll show you how to calculate how many turns you need. I used #18 Thermalese wire for the primary winding (I got mine from The Wireman). In the process of winding the toroid you need to make several “taps”. There are various ways to do this. Figure 1 shows the way I did it. It’s harder to describe than to do. Basically, when you come up on a turn that requires a tap, use a Dremel tool or some sandpaper to scrape off the coating for a centimeter or so, then form the uncoated segment into a loop. Using pliers, grab the loop and turn it 180 degrees, so that the free end of the loop naturally continues along the winding path of the coil.

Toroid tap

Figure 1. Forming a "tap".

The “high” impedance and “low” impedance secondary windings are important. I used #20 wire and wound them both between the windings of the primary. The goal here is to achieve a good, tight coupling between the primary and secondary.


Try as much as possible to use straight, short connections. Keep the capacitors away from ground as much as possible. I used ceramic, feed-through insulators for my output connections. That is not necessary. Banana jacks from Radio Shack are just as good. I used a heavy-duty DPDT switch for the high and low impedance output links, but a small switch might suffice. See Figure 2.

Hi/Lo Links

Figure 2. Notice the ceramic feed-through insulators
and the heavy duty DPDT switch.

Use marked dials for both capacitors if you can find them. I couldn’t, so I made my own dial markings. I used Paint Shop Pro to make 20 markings per 180 degrees of the dial. I decided to increment the numbers on my dial counterclockwise to show relative capacitance. Because I used a black enclosure, I had to print white on black to get contrast. I used double-sided tape to affix labels to the enclosure. See Figure 3.

Dial Markings

Figure 3. Dial markings made with Paint Shop Pro.


I used the MFJ Antenna Analyzer (259B) to run initial tests of the z-match. I resisted the temptation to use my Jupiter (I had visions of a “smoked” Jupiter). I was amazingly lucky: my initial tests showed that the z-match tuned my antenna on all bands from 80 through 10 meters (both phone and CW segments). I was able to obtain a 1:1 SWR on all bands. I made extensive notes on the dial settings and output link used for each frequency. My tuner required no changes from the z-match described by W6JJZ.

I noticed immediately that C1 acted almost like a “band-switch” i.e. it remained pretty much constant while tuning a particular band. In addition, tuning C1 was not critical on most bands. Merely getting C1 “close” was sufficient. Not so with C2...C2 tuning was much more critical: in fact, on some bands C2 was “very” touchy. This is a known characteristic of the z-match and you should be prepared for it. Still, as touchy as it was, I could re-tune a frequency pretty much using only my dial markings, along with peaking the noise on the receiver (see suggestions below).

Notice that I took W6JJZ’s suggestion and used a SPST switch to connect both sections of C1 in parallel. I switch in both sections only when necessary. I labeled the switch 370 and 740 pf, because that’s what my BK Precision LCR meter indicated. The lower the frequency band, the more capacitance you need for C1. I use the 740 pf setting for both 80 and 40 meters. I use one section of C2 (370 pf) for all bands from 30 to 10 meters. See Figure 4.


1. Use the largest capacitor you can find for C1. You might also consider using one or more silver-mica capacitors in parallel with C1. Make all capacitance switchable, as shown in the schematic. Remember, you’ll need low capacitance for some bands, so don’t hardwire the sections together. Use a switch. See Figure 5.

Capacitor Wiring

Figure 4. Notice how the caps are wired.

2. Get “broadcast quality” capacitors if you’re likely to run more than 100 watts. Look for big capacitors at hamfests.

3. Consider a vernier for C2. You can live without it, but C2 can be touchy.

4. If you can’t get a match on one or more bands, change the length of the feed line. Add about 1/8 wavelength for the problem band to the existing feed line and try again. Don’t be afraid to splice ladder line or twin lead. After adding feed line, you may change settings on other frequencies. You might also consider changing the number of turns for the high and low impedance links. It might take a while to achieve good results on all frequencies.

5. If you’re a shortwave listener, consider a bypass switch for the tuner. The z-match acts as a mighty good pre-selector (a good thing, ordinarily, but not for shortwave listening). For example, if I tune the z-match for 40 meters, I can just about hear KEEL on 710 kHz, which ordinarily comes in 40 db over S9.

6. Consider adding a second PL-259 for output with a switch for unbalanced line. You may need to tune a coaxially fed antenna some day. The z-match handles both balanced and unbalanced antennas.

7. Consider building an air coil version of the z-match. This should be easy with a little calculation and experimentation. The full primary of the toroid is a little over 5 µH. This should be easy to achieve in a coil, but beware that the diameter to length ratio of the coil is a factor.

8. Experiment with this tuner and report your findings to the club.

Conclusions and Final Thoughts

This is a good little tuner. It cost me about $60 to build, which is a little expensive for a small tuner. However, it got me reading about tuners and gave me building experience, which counts for something. If you calculate the number of dollars per hour of fun I’ve had building and testing this tuner, it’s the best buy in town.

Do some reading about tuners and I think you’ll find they are much more complicated than you thought. For a glimpse at the mathematics of ATU’s, read Dr. Cebik’s series of articles on link-coupled tuners on his website 5.

All tuners have problems with some load conditions. I’ve put the little z-match through its paces over the past few months and I must admit that I like it. I plan a series of measurements and tests on the z-match. I’m in the process of building another version.

Have fun and 73.


1 Lew McCoy, “Lew McCoy on Antennas”, CQ Communications, Hicksville, NY, 2002, pp. 58.
2 Press Jones, “The Wirebook IV”, The Wireman, Inc., Landrum, SC, 2002, pp. 6.2.
3 Jim Parise: QST Reviews Five High-Power Antenna Tuners, QST Magazine, pp. 69-75, Feb 2003.
4 L.B. Cebik, “10 Frequency Asked Questions about the All-Band Doublet”, http://www.cebik.com/wire/abd.html
5 L. B. Cebik: “Link-Coupled Antenna Tuners: A Tutorial”, Parts 1-5, http://www.cebik.com/link/link0.html
6 Charlie Lofgren, “The Z-Match Tuner: An Update”, http://www.seboldt.net/k0jd/z-match.html
7 Phil Salas, “A Compact 100 W Z-Match Antenna Tuner”, QST Magazine, Jan 2003, pg. 28-30.
8 Lloyd Butler, “Output Balance on the Z-Match”, http://www4.tpgi.com.au/ldbutler/Zbalance.htm

ZM Schematic

Figure 5. A schematic incorporating some of above suggestions.