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How is my doublet doing.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 2E0LPL, Jul 11, 2019.

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  1. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Hi guys had a go at constructing my first 450 ohm ribbon fed doublet.

    Each leg is around 21.5 side of it is in clear air...the other half has to pass over my house roof and comes within 1mtr or the roof ridge....the ribbon feeder is 20ft long leading to my upper floor shack.

    Its also in a Z shape to fit in my lot.

    Never used ribbon feeder before so I am learning on the job and have a few questions.

    On hooking up to my analyzer to my balanced line feeder ATU with its 4-1 balun set to by-pass I find none of the lower HF freq have low SWR reading...some readings as follows.

    80m 3500khz 7.28-1 149 ohm....3800 khz 9.66-1 367 ohm

    40m 7000khz 6.8-1 10 ohm 7200khz 6.43-1 6 ohm

    30m 10.000khz 5.04-1 64 ohm 10.200khz 4.27-1 47ohm

    20m 14.000khz 9.70-1 116 ohm 14.300khz over 10-1 116 ohm

    15m 21.000 3.99-1 7 ohm 21.300khz 3.5-1 7 ohm.

    Tuning is patchy on 40m...but generally it tunes but could be improved.

    Anybody give me some idea on how those figs I say my first entry into using ribbon feeder and doublet antennas.
  2. AI3V

    AI3V Ham Member QRZ Page

    Numbers look fine to me.

    Doublet here is around 180 feet total (not measured- that's how far the best two trees are), installed as a inverted "V" about 60 feet at the apex (that's how high the best branch is), with around 90 feet or so of open wire line going to the transmitter (that's how far apart they were).

    I spaced the owl about 5" apart, cause that looks nice to the xyl :)

    Tunes fine (little Ten-Tec manual tuner) and gets out ok 160-10meters.

    I havn't a clue what the vswr is.

    AF7XT likes this.
  3. K2XT

    K2XT Premium Subscriber QRZ Page

    The resistive part of all your impedances are quite low, on all bands. That is suspicious.
    I'm guessing you may be measuring at the input of the atu?
    If so, measure at the end of the feedline, with no balun, just looking into the transmission line, and repost some sample readings.
  4. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Ok will do.

    Even though my ATU is set to by-pass for those measurements...I suppose its still running through the 4-1 built-in balun.
  5. WR2E

    WR2E Ham Member QRZ Page

    Try a 1:1 balun too...
  6. W5DXP

    W5DXP Ham Member QRZ Page

    WB5YUZ and AF7XT like this.
  7. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Ok hooked up the ribbon feeder into my analyzer direct...yes different figs indicated.

    Resonate at 2900khz 1 to 1 swr 34 ohm

    3500khz swr 7.21-1 153 ohm......3800khz swr 9.34-1 351 ohm

    7000khz plus 10-1 swr 146 ohm....7200 plus 10-1 swr 124 ohm

    14000khz swr 8.83-1 366 ohm 14300khz swr 9.27-1 397 ohm

    21000 swr plus 10-1 319 ohm 21350 swr plus 10-1 285 ohm

    each antenna leg is around 21.5 mts....450 ohm ribbon feeder aprox 20ft long.

    Is that looking any better Rick.
  8. KE6EE

    KE6EE Ham Member QRZ Page

    Looks good for being tunable with a wine-range manual tuner.

    Your previous measurements suggest that the 4:1 transformer or balun is producing a low
    Z value that your tuner is having a problem matching on 40M. As already suggested you should do better with a 1:1 balun.

    It might be helpful if you would describe exactly what kind "balanced ATU" you are using. If it's a balanced
    tuner, then you don't need a balun on the tuner output because the tuner is a balanced tuner. ;)

    See AI3V's comment. Easy peasy.

    I have a 200 ft. doublet fed with about 40 ft. of window line. I can tune it on any band from 160M to 10M with
    my wide-range manual tuner. Easy peasy.

    If you want your antenna to work on most bands 80M and higher in frequency either use a wide-range manual
    tuner or refer to W5DXP's website for adjusting antenna and feed line lengths suitable for a narrow-range built-in
    tuner. With a 1:1 balun.

    You should have all the advice you need already posted. I have merely summarized it for you.
  9. K7KBN

    K7KBN Ham Member QRZ Page

    Tell us more about this "wine range manual tuner...":D
    NH7RO likes this.
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    Negative! The numbers on all but 80m are all in a range where a T-network tuner will be lossy. The 1:4 balun at the output of the tuner is also being stressed, and will also be lossy. Lose the 1:4 balun, and replace it with a high-quality current-mode 1:1 balun.
    WB5YUZ likes this.

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