Coaxial stub matching of the .64 lambda antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 2E0VSS, May 30, 2012.

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  1. K4SAV

    K4SAV Ham Member QRZ Page

    There are several ways to match this. A series 2.7 uH coil won't do it. A series 5 uH coil should get the feedpoint impedance down to 100 ohms. If you use a low loss matching network, it should be about 1 to 2 dB better than the quarter wave vertical for elevation angles below 14 degree. Between 18 and 28 degrees it will be about the same or maybe a little less gain than the 1/4 wave vertical. Above 28 degrees the 0.64 wavelength will be significantly better, but there are very few signals on 20 meters arriving at those angles.

    I didn't look at sloping the radials since you said you can't do that. That changes the feedpoint impedance and the take-off angle.

    Jerry, K4SAV
     
  2. 2E0VSS

    2E0VSS Ham Member QRZ Page

    Ok, understood Gerry. If I go the 5uh coil route can I then use a manual balanced T match tuner to do the rest at the Tx. My RG 58 lenth to the feed point will be around 20 feet.
    I guess I could tap the coil for the best match? I'm guessing that the 100 ohm Feedpoint will yield a lowest SWR of 2-1 with horizontal radials Gerry?

    Mark M6AWG
     
  3. 2E0VSS

    2E0VSS Ham Member QRZ Page

    I beg your Pardon Jerry.. Its popular here to spell your name with a G, I'm sorry.

    M6AWG
     
  4. K4SAV

    K4SAV Ham Member QRZ Page

    I'm not sure if it is possible to match it with a taped coil or not. I would use an LC network, about 4 uH series to the antenna and 10 pf across the coax. There are other possibilities.

    Antenna feedpoint impedance to be matched is about 100 - j500.

    Jerry, K4SAV
     
  5. W5DXP

    W5DXP Ham Member QRZ Page

    Seems to me, if the inductive reactance of the coil equals the capacitive reactance of the antenna, then any tap point on the coil will be purely resistive and somewhere it will equal 50 ohms.
     
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