Multiband Wire Antennas
    By Ed Humphries - N5RCK

    The March 1991 issue of CQ Amateur Radio contained yet another
    discussion of multiband wire antennas. In his column "Radio
    FUNdamentals", Bill Orr, W6SAI writes about the original W9CXX
    multibander with its' complex copper tubing matching section.
    He then goes on to discuss the popular G5RV developed by R.
    Varney, which is widely built and commercially available. Orr
    points out the deficiencies of the G5RV: when built in the
    original design it delivers reasonable SWR on the 7, 14, and
    24 MHz bands, but into a 75 ohm coax feedline that is awkward
    to load up on modern transceivers; when built with 50 ohm coax
    the SWR is poor on all bands, but it performs reasonably well
    when used with a "transmatch" antenna tuner.

    The column skips over an intermediate antenna design discussed
    in the March 1986 issue of Ham Radio. Bill's column back then
    pointed out that W5ANB first proved you could successfully
    modify the G5RV, load it with 50 ohm coax and run without any
    antenna tuner. But the best design (so far HI) he discusses in
    both articles is the one by ZS6BKV. Brian Austin used computer
    modeling to help him design a 5 band tuner-less antenna. Orr's
    CQ column reprints the design using only the dimensions for a
    300 ohm matching section (I presume TV flat lead qualifies).
    In his original column Orr also presented the figures for using
    400 (handmade open-wire leads) or 450 ohm (ladder-line) as the
    matching section. Since 450 ohm ladder-line is somewhat stronger
    than the commonly available 300 ohm TV lead-in, I'm here giving
    both sets of figures so you can make your own choice.

    <  90' 3" for 450 ohm matching section or 92' 2" for 300 ohm >
    o-----------------------------oo-----------------------------o
                                      ||
        The ZS6BKV Antenna            ||
                                      ||
                                      || 40' for 450 ohm
                                      ||
                                      || 36' 9" for 300 ohm
                                      ||
                                      ||

    At the end of the matching section Orr recommends a 1:1 balun;
    others would say that several loops of coax at the feedpoint
    will do as well to help keep rf off the feedline. The feedline
    to the transceiver is common 50 ohm coax; RG 58/U is fine for
    hf for most runs. This antenna should give low SWR on 7, 14,
    18, and 24 MHz bands. At 28 MHz the SWR is really only good
    from 28.5 to 29.0. Tests showed the best SWR curves when the
    antenna was erected at about 42 feet above ground. When run as
    an inverted-V (90 degree) the resonant frequency came down 80
    kHz for 14 MHz and 125 kHz for 24 and 28 MHz. The March '86
    article printed SWR curves, and the March '91 article printed
    field patterns for all 5 covered bands.

 * Origin: Ham Echo Moderator / HDN Coordinator (214) 226-1181 (1:124/7009)