inverted "V" without a balun?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB3SJQ, Dec 31, 2009.

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  1. KB3SJQ

    KB3SJQ Ham Member

    Hello fellow hams,
    My father and I are looking for a simple QRP antenna.
    My question is:if I make an inverted "V" antenna without a balun(solder one wire element to the center conductor and the other to the shielding of the coax), keep the wire sides at a steep angle, and don't hang the antenna very high,will the impedence of the wire match to the impedence of the coax well enough to have a low SWR?
    Thanks in advance!
    KB3SJQ
     
  2. KT6F

    KT6F Ham Member

    In the old days I ran an inverted V quite effectively and worked a lot of DX. It would easily tune all the HF bands except 160. 80 meters took a little work to tune and I had to re-tune if I moved much off the tuned frequency. I fed it with 300Ω twin lead and an antenna tuner. The elements should be split in the center and each leg fed with one of the twin lead conductors. There will be no balun required and twin lead is lostless.
     
  3. W0IS

    W0IS Ham Member

    It will work fine. That´s what I´m using at home. I was planning on using a balun, but the local radio emporium was closed the day I put it up, so I went without.
     
  4. G3TXQ

    G3TXQ Ham Member

    I think you may be muddling two different issues:

    1) Depending on the band, your ground conditions, and the antenna height, an Inverted-V will probably be a reasonable match to coax feedline.

    2) The need for a balun is a different issue. Think of the outer surface of your coax braid as forming a completely separate antenna wire; it's connected to one side of your antenna and comes all the way back into your shack - possibly close to TVs, radios, computers, phones etc. Does that sound like a good idea? If not, you need a 1:1 current balun - also known as a common-mode choke - at the feedpoint.

    73,
    Steve G3TXQ
     
  5. KB3SJQ

    KB3SJQ Ham Member


    Thanks for mentioning that. It was a point that I had not considered.
    I think that I will just use twinlead instead and feed it to a transmatch like the other fellow mentioned.
    Thanks,
    kb3sjq
     
  6. KT6F

    KT6F Ham Member

    The length of your elements need to be adjusted to match the twinlead impedance. I don't remember the length off the top of my head. I know I've got it somewhere in some ancient ham pub though. You might search Google, but I'll look around...
     
  7. KT6F

    KT6F Ham Member

    Found it. Here is the antenna I used for all HF bands. After erecting beams for 15 and 10 I continued to use the inverted V for the lower bands. The instructions indicate a split feed line but the twin lead worked perfectly as well.

    [​IMG]
    [​IMG]

    Reference: ARRL Hints and Kinks for the Radio Amateur (1968)
     
  8. AE5JU

    AE5JU Ham Member

    A low dipole can tend to be low in impedance, lower than the ideal 50 ohms, which results in higher SWR. This can be remedied by offsetting the feedpoint a bit. That is, make one side a few feet longer, the other side shorter by the same amount. This shifts the feedpoint over to a point nearer 50 ohms.

    Choke balun by the feedpoint, you can simply put some ferrite beads on the coax right up by the feedpoint. I use 5 snap on beads (Palomar Engineers FSB-1/4) for one portable antenna which the lowest band is 40 meters. I use 10 beads on another portable antenna which the lowest band is 80 meters.

    These are the same beads:

    https://www.hamcity.com/store/pc/viewPrd.asp?idcategory=655&idproduct=1830


    I highly recommend this center section by Jetstream:

    http://www.universal-radio.com/catalog/antsup/5363.html

    It is inexpensive, ruggedly constructed, and will make for a longer lasting, more troublefree dipole antenna.
     
    Last edited: Jan 1, 2010
  9. WD5ABC

    WD5ABC Ham Member

    You guys are making this harder than it has to be. If you do like you said and feed it with twin lead through a tuner with a balanced output, it will work fine. It might be better to make it resonant on the band you're using, but even that's not critical. For QRP, you need the least loss you can get, the twin lead or ladder line will do that for you and make it easy to match.

    Happy New Year and enjoy QRP!
    Kerry, WD5ABC
    (Using an 80m dipole fed with twin lead on all bands)
     
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