Connect with us

Log-Periodic Antenna Design

Discussion in 'Electronic Design' started by Rich Grise, Nov 19, 2008.

Scroll to continue with content
  1. Dave

    Dave Guest

    Log periodics are not necessary for sub-octave operation.

  2. GregS

    GregS Guest

    I did the same thing and I was surprised how many digital chanels I got.
    I was at a dollar store and saw the RCA UHF/VHF loop/ears for $5 and
    that gave me considerable better reception.

  3. GregS

    GregS Guest

    Ever hear of the BOW TIE. Its a sort of Fractal antenna. Having a wide band.
    It could be improved by making it a full fractal.

  4. John Smith

    John Smith Guest

    Actually, I had to construct my own with a broadband MMIC device, to get
    decent functionality ... however, my mother has an el-cheapo unit she
    purchased from some yard sale, it/they work surprisingly well!

    Location, reflections, etc. can vary ones experience greatly--but hey,
    they usually beat a wire coat hanger! :)

  5. Guest

    I have used the procedure in the following paper:

    I slightly modified the design (e.g. I used several different
    diameters for the elements), but basically I used the same formulae.
    I did not use their formula for deciding the right spacing between the
    support tubes to get the right characteristic impedance, because I
    suspect that maybe it is only valid over a limited range of spacing.
    Instead, I measured the characteristic impedance of just the tubes
    with no elements attached on a VNA that could plot impedance vs
    distance in a sort of TDR mode, and I adjusted the spacing until it
    was right. I epoxied some very small (roughly 1mm cube) spacers
    between the support tubes to keep the distance right, once it was
    adjusted properly. It is important that the space between the support
    tubes is mostly filled with air, not epoxy or any other dielectric,
    because the wave needs to propagate at the right speed between the
    tubes so that the elements are fed in the right relative phase, and
    this won't happen if there is something with a higher dielectric
    constant in there. I used those brass tubes that you can get in hobby
    shops, but unfortunately brass is fairly resistive and I did not
    silver plate it. I would have used aluminium if it were easier to
    solder in a reliable way.

    The finished antenna had a good return loss over the desired frequency
    range (sorry, can't remember the numbers) and it did the job for which
    it was intended although I don't have a measured gain value etc.
    because I don't have an antenna range.

    I have a spreadsheet for calculating the element lengths (in format) if you are interested.

  6. Rich Grise

    Rich Grise Guest

    Cookbook, if at all possible. Like, element lengths and spacing,
    and the angle between the booms - which brings up a question - what
    effect does it have when you take a flat L-P and "open it up", like
    to a pyramid shape - I was doing a thought experiment with this and
    when it's completely "flattened out", (180 degrees between the booms),
    it looks like a <drum roll please> Bow Tie!

  7. Rich Grise

    Rich Grise Guest

  8. Rich Grise

    Rich Grise Guest

    Hey, "John Smith", why don't you go outside and play

  9. Rich Grise

    Rich Grise Guest

    "Best Regardses"? ;-)

    Anyway, thanks for this - I'm feeling a lot better about this project now
    thanks to your help and that guy that translated it for me (forgot the
    name, but he knows who he is - Thanks Again!);

    I might even start cutting wire[1] and soldering this weekend! ;-)


    [1] GTAW (Gas Tungsten Arc Welding) filler rod, with some coppery-
    colored coating that solders even better than copper, about .030 dia.,
    and as stiff as piano wire.
  10. Rich Grise

    Rich Grise Guest

    Apparently I'll only need up to ch. 52; have to look up the carrier freq.
    on that.

    Ch. 14 = 470-476 MHz
    Ch. 83 = 884-890 MHz I think.

    Now all I need to do is the algebra. ;-)

    52 - 14 = 38
    38 * 6 = 228
    228 + 470 = 698
    698 + 6 = 704

  11. Rich Grise

    Rich Grise Guest

    Dude! Awesome! And this one doesn't even have a reflector!. I
    wonder how far I should hang it in front of the venetian blind. ;-)

  12. Mark Zenier

    Mark Zenier Guest

    Your clip lead is too long. Try 1/4 wave.

    I got good reception using a 4 1/2 inch length of 24 gauge solid poked
    into the F connector for a (line of sight) 45 kW station, 20 miles away.
    (Most of the local stations run in the 500-1000 kW range).

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
  13. Rich Grise

    Rich Grise Guest

    Yes - somebody just pointed to a youtube of somebody making one out
    of coathangers.

    I think I'm gonna do that.

  14. Jim Lux

    Jim Lux Guest

    Orfanidis's book on electromagnetic waves and antennas is online, and
    covers LPDAs.. Kraus is better, but you'll have to fork out at least
    $20+shipping for a used copy. Kraus *is* my recommendation if you have
    to have a single antenna book, though.
  15. Cecil Moore

    Cecil Moore Guest

  16. John Smith

    John Smith Guest

    LOL ...

    Darn, you just can't get decent psychiatric help with your food stamps,
    can you? :-(

  17. NoSPAM

    NoSPAM Guest

    Standard, indeed; this antenna is known as a biconical. It has excellent
    wideband response making it ideal for EMC testing. Most good antenna texts
    such as that by Krauss give a detailed analysis of the biconical antenna. I
    see no relationship between its design and a fractal design other than both
    are wide bandwidth antennas.

    The bowtie antenna which Rich and others have mentioned is a "flattened"
    form of the biconical. If the bowtie is bent along its major axis, it makes
    an excellent wideband driven element for a corner reflector antenna.

    73, Barry WA4VZQ
  18. Rich Grise

    Rich Grise Guest

    I read it in a QST or so back in the 1960's. :)

  19. Rich Grise

    Rich Grise Guest

  20. It doesn't.

    I have two converter boxes, one Magnavox, one Zenith. I just now tried my
    local stations with them using a straight 24-inch alligator clip lead as the
    antenna. Location is a residential garage in the San Diego suburbs. Stucco
    walls, metal garage door closed, overhead fluorescent lights on.
    Transmitters in three different locations.

    All the UHF locals came in, 10 transmitters with about twenty total
    programs. The one low-power VHF did not. Looping the clip lead back and
    clipping the end to the F-connector produced about the same results. (Lost
    one TJ station.)

    When I "upgraded" to a POS 2-bay bowtie in the rafters (about 8 feet up),
    all eleven locals came in, plus KCBS from LA . On the Zenith box, arguably
    a better unit, I got two more LA channels, although one of them had some
    intermittent freezing and tiling.

    If even poor antennas work well, why all the whining?

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day