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Z-Match tuner questions W/pictures

Discussion in 'General Technical Questions and Answers' started by VK2ZYZ, Sep 9, 2007.

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  1. VK2ZYZ

    VK2ZYZ Ham Member QRZ Page

    Hello all, name here is Charley, QTH is Wauchope, Australia. I am currently homebrewing an Antenna tuner, well, actually attempting to rebuild a pile of tuner parts into something resembling a tuner. Ok, I'll start with the rig, Kenwood TS120S, Tandy SWR Meter( I know, not the best choice but $16AU) Bencher Paddles(The best choice), Homebrewed Keyer using the curtiss chip(Flawless performance) The antenna is an 80M Dipole, 20 feet up, fed with a 1:1 Ugly balun, and about 50ft RG8. Best I can tune the Antenna (no Tuner) is 1:1.75.

    The tuner: a local ham gave me an old wooden box fitted with the Caps and coils, all of the solder joints had started to die and the wood was crumbling, so I disassembled is, drew the schematic, checked it against a basic Z-Match tuner, seemed correct so I reassembled the whole mess with new hook-up wiring inside an old cumputer case, It's not pretty but total cost is <$5 so far.
    The Tuner is able to tune the 1:1.75 dipole antenna to 1:1.1 no problems, but it wont tune the dipole to any other band, I have tried about everything I can think of and find on the net with no, or little improvment. Is it worth continuing with the two coil Z-match or should I convert the whole thing to a single coil Z-match tuner, and ANother question, can I wind the new coil using large guage electricle copper wire as I used for the wiring in the tuner now.

    The pictures: the first picture is of my Ham shack, not much, but still heaps of fun. The second pic is the schematic, I hope you can understand my chicken scratches. And the third pic is the inside of the tuner, definately ugly construction here, the black coil was a modification I attempted with no difference.

    Any help is greatly appreciated, and thank you for taking the time to read this long winded post.
  2. W5DXP

    W5DXP Ham Member QRZ Page

    Aside from the tuner not tuning, you have a system problem. The feedpoint impedance of the 75m dipole is about 7000 ohms on 40m according to EZNEC. That's an SWR on the coax of about 140:1. Essentially the same thing is true on the other bands. Most hams using 75m dipoles for all-HF-band operation use ladder-line or open-wire line. With a Z0 of 600, the SWR is only about 12:1 on the open-wire line on 40m.

    Solution: Switch to ladder-line and adjust the length of the ladder-line until the tuner will tune it. Some idea of what you are up against can be had from:
  3. W4HAY

    W4HAY Ham Member QRZ Page

    Nice job, especially the coils!

    Getting a 1/2 wave dipole to work on anything other than the frequency for which it is cut (except 3/2 wave) is tricky, and line losses will be high.

    One solution would be to use ladderline feeders, and a balun at the tuner to feed the balanced line. You can make the feedline from copper wire and plastic rods for insulator/spacers.

    Alternately, do a search on the W3DZZ dipole. It's a compromise, but can be tuned for 80, 40, 20, 15, and 10 Meters. I use one with 50 Watts and have no problems working DX, even with the sun refusing to cooperate.
    I slung separate dipoles beneath it for 30 and 17.
  4. K3WRV

    K3WRV Guest

    A couple of points:
    1. A COAX fed antenna won't be useable on most bands, the exception being that it will work on it's third harmonic. 3.5 mc should work on 10 mc, and 7 mc works ok on 21.
    On the other bands, the impedence at the fed point is high, so you'll lose most of your power in the tuner and heating up the Coax.
    2. Remember that a tuner (unless placed at the antenna feed point) ONLY matches the apparent impedence of the antenna SYSTEM to the output of the transmitter. It doesn't match the impedence of the antenna to the line. And baluns and Coax get unhappy when used to feed an impedence other than what they were designed for.
    3. If you want multiple bands on a dipole, use open wire/ladderline/twinlead, and it should work. Or make a fan dipole, with 40 and 20 slung underneath the 80.
    4. Using larger guage wire for the coil is just fine - it will handle more power.
    5. Been a long time since I've used a Z-match, but you might also try an L network. It should work fine if you convert the 80 M dipole to a fan dipole and don't want to ditch the Coax.
    [EDIT] I crossed with the two previous posts].
    [FURTHER EDIT] - Try reconstructing your tuner for a balanced output - IIRC, the Z-match is inherently balanced, and use twinlead or ladderline. TV twinlead shoul;d work up to 150 W or so.
    de Bob
  5. WA2ZDY

    WA2ZDY Guest

    As said, change the coax to ladder line, get rid of the balun at the feedpoint, and either arrange the tuner for balanced output, or use a good 1:1 current balun at the output of the tuner to the feedline.

    Most baluns designed to be used as dipole centers are voltage type and are undesireable.
  6. VK2TIL

    VK2TIL Ham Member QRZ Page

  7. VK2ZYZ

    VK2ZYZ Ham Member QRZ Page

    I wish to thank every one for there helpful responces. Weighing up my options I decided to add a 40m dipole to my existing 80m dipole, that way I am powering the antenna instead of the tuner. I would love to switch to Ladder line, but it is hard to get here and very expencive. What I've done is connect 40m legs to the center insulator on the 80m dipole and tied the ends about 30 degrees clockwise to the side of the 80m legs, I couldn't hang the 40m dipole under the 80m because of obsticals. I trimmed the 40m antenna to the best swr I could get without the tuner, again being about 1.75:1 and then the tuner easily tunes the antenna to 1.1:1. So far the 80m and 40m dipole antenna, coax, fittings, tuner and SWR meter have cost me a total of $75 thats about $50US, proving you don't have to be rich to enjoy Ham Radio. Eventually I want to go up a few more feet, currently I am 20 feet up and I would like to go up another 12 feet. Or even better a 100 foot tower, but thats just a dream at the moment. Again, I would like to thak everyone for there help.

  8. KA9VQF

    KA9VQF Ham Member QRZ Page

    Depending on what you have for wire available it really isn’t that hard or expensive to make ladder line.

    Way back when I was just a tad I built some. The book I got the directions from said it would be 600 ohm when finished.

    I was allowed to use my dads table saw and drill press all by myself. I used an old oak pallet for spacers. The spacers were around 1” wide ¼” thick and 7” long with holes drilled at 6” for the wire to go through.

    The directions said to put a spacer every 18” but I decided there would be to much of an opportunity for it to get crossed up so I put them every 6”. this probably added some unnecessary weight but it did seem to me that it kept the thing from getting tangled together.

    For wire I used common rubber coated zip cord like used for lamps and other light appliances. Back then a 100 foot roll only cost around $5.00. I split the two wires apart before I put them in the holes in the spacers.

    To keep the spacers from just falling back down the wire once it was strung up I used shellac, I’d put a coat of shellac on the spacers before I strung the wire through to try to protect them from the weather. Once it was strung together i just put another dap of shellac right where the wire came through the holes.

    In these modern times I would probably use a UV resistant polyurethane instead.
  9. W4HAY

    W4HAY Ham Member QRZ Page

    Spacer idea: plastic clothspins, or wooden ones boiled in paraffin.
  10. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    Hi Charley,
    Are you sure this is a transmatch (or ant coupler)?
    Based on the schematic, it has 3 ports.
    Looks more like a phasing unit or combiner or some other
    73, Pete
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