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Log-Periodic Antenna Design

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

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  1. Rich Grise

    Rich Grise Guest

    My current UHF antenna is a 14" Radio Shack clip lead clipped from the
    center of my coax to the venetian blind. I have to hand-adjust it
    for the channel, weather conditions, phase of the moon, etc. I can
    do this because I can _see_ an indication of signal strength.

    Well, with this new Fascist "No More Free TV" crap, I'm gonna need
    a real UHF antenna. My budget is exceedingly limited, but I have
    a supply of materials (GTAW filler rod, with some coppery-colored
    coating, so it solders like a dream, and is as stiff as piano wire)
    to build an antenna with.

    But I've been searching the web for some weeks now, and I can't
    seem to find any kind of formula, except there was this program
    I downloaded - LPDA.EXE, which runs on DOS. Unfortunately, it's
    in Russian or Polish or Uzbekistani - one of those East Yurp
    languages. Here's a screen snap:
    http://mysite.verizon.net/richgrise/images/LP-Prog-Output.gif

    Which I went through pretty much by-guess-and-by-gosh - can
    anybody read that stuff?

    There are a lot of factors I don't know about, like "Tau", and
    all of the specific designs on the web are flat - something is
    telling me I want one of those pyramid-shaped ones, but I really
    don't know the difference (between that and flat) - it's probably
    something to do with bandwidth or F/B ratio or whatever.

    My local library has no ARRL Antenna Book (!), and did I mention
    I have a seriously limited budget?

    So, how do I pursue this? It'd be nice to have a program that will
    calculate the whole thing for me, but am I dreaming? If I want to
    send myself to Log-Periodic School, where should I start?

    Or, does anyone have a UHF-TV log-periodic design that they'd share? :)

    Thanks,
    Rich
     
  2. Are you seriously THAT hard up for cash? :->
    Try this - go to your local hardware or whatever store that sells a
    suitable log-periodic antenna with camera and tape measure in hand.
    Record it all and then go home and duplicate. Or easier still, buy it,
    take home, duplicate, then return for a refund.

    Dave.
     
  3. Carl Ijames

    Carl Ijames Guest

  4. You don't really need a new antenna. If your current antenna is working
    such that you get a good picture then it should work as a digital tv
    antenna.

    Another Dave
     
  5. Jim Lux

    Jim Lux Guest

    Interlibrary loan is your answer. Your library may not have it, but
    someone else's does.

    Looking for a cookbook design, or the theory to do it yourself?
     
  6. TheM

    TheM Guest

    Upisi najnizju radnu frekvenciju : enter lowest frequency
    Upisi najvisju radnu frekvenciju : enter highest frequency

    Duzina antene: length of antena
    Broj elemenata: number of elements

    Pritisni taster za proracun antene: press a key to calculate antenna

    Duzina 1. elem. length of first element

    Pritisni taster za nastavak Press any key to continue

    Duzina zavrsnog kratkospojenog odsecka: length of final shorted section
    Upisi precnik dipola: enter diameter of the dipole

    Upisi ulaznu otpornost (ohm): Entry resistance (weird in original)

    Impedanca napojnog voda: feeder impedance (not sure what this is)

    Upisi precnik napojnih provodnika: diameter of feeding leeds (my guess these are two bars that hold elements)

    razmak izmedju napojnih provodnika: distance between feeder leeds (and distance between two bard holding elements)

    You owe me a beer. BTW, its Croatian or Serbian. I kind of understand some 90%.

    M
     
  7. Rich Grise

    Rich Grise Guest

    This won't do at all! Two of my favorite stations are ch. 56 & ch. 58.
    =:-O

    I've got 2-13 covered by my external VHF folded dipole. (It's an RV).

    Are the channel frequencies going to be all changed around? I suppose
    I should email those two stations. I don't know much about DTV, other
    than I have to buy a damn box and I need a "better" antenna.

    Thanks,
    Rich
     
  8. Rich Grise

    Rich Grise Guest

    Thanks, but that thing's HUGE! I was thinking something more along the
    lines of 1' square. (or a 1' cube)

    Thanks,
    Rich
     
  9. Rich Grise

    Rich Grise Guest

    I've heard that there's no "signal strength" meter or anything - it's
    either there, or not. With my analog, I can zero in on the proper tuning
    (I just futz around with the clip lead until it's "good enough") so
    I need something I don't have to screw around with.

    Thanks,
    Rich
     
  10. Most digital STB's have a "signal strength" indicator on screen for
    each channel.
    That's true of the displayed picture, but not the signal.
    Poor (or even too much) signal strength can lead to "drop outs" or
    "freezing" of the video image.

    Dave.
     
  11. Yes.
    Channels will vary depending upon your country and location. You
    should have some sort of official digital TV website for your country
    that lists and explains all this stuff.
    Australia for instance is:
    http://www.dba.org.au/
    (server down?)

    Dave.
     
  12. mpm

    mpm Guest

    I agree. How much can a coat hanger cost?
    If you are really rubbing pennies together, I would ditch the log-
    periodic approach and go with something simpler, like a monopole or
    folded unipole antenna. (All you need is wire.)

    I just want to mention (again) here that: Hopefully, we'll be able to
    knock out Ch-5 and Ch-6 from this antenna scenario very soon (and move
    them to the FM Band, as the FCC is presently considering. I'm a huge
    proponent of this possibility!

    I will try to find the Comments link at the FCC web site so those of
    you who agree can chime in....

    This idea has been floated before, of course. This time it seems to
    have "legs".
    I don't know how much you can read into it, but... the FCC has yet to
    explain how Non-Commercial Educational (NCE) vertical only stations
    can obtain authorization for horiz/vertical operation once this DTV
    transition occurs - which is now less than 90 days away.

    There are many pending Construction Permits (CP's) and NCE facilities
    that proposed Vertical-Only operation in order to protect local ANALOG
    TV-6 stations. These new NCE facilities will undoubtedly delay
    construction until a decision is made how to obtain dual polarization
    licensing. (Due to increased transmitter power requirements and/or RF
    Safety exposure issues, tower height requirements, etc..)

    To date, the FCC has yet to adopt ANY relaxed TV-6 digital protection
    criteria for NCE FM stations. Instead, these stations must use the
    old Analog standard - which is MUCH stricter than is necessary to
    fully protect a Digital TV operation!

    And of course, there are only (8) full service TV's on digital channel
    6. (Which is a really, really good reason to move TV-6, and possibly
    TV-5 to the FM band!! -- What a huge waste of spectrum!!) Yes,
    there are some low-power DTV 6's out there (translators, boosters,
    LPTV's). Not very many, and all of which are in locations where other
    spectrum is, or will be, avaialble after the DTV transition...

    Anyway, any NCE or CP not near a digital-6 would obviously qualify for
    dual-polarization. It remains to be seen what the FCC will do about
    this. Hopefully, they will grow a brain and shift this "un-used"
    spectrum to alleviate the very crowded FM band.

    I don't know if I should hold my breath or not.?

    -mpm
     
  13. mpm

    mpm Guest


    Oops. that post was directed at Rich.
    My apologies for responding at the wrong thread entry point...
     
  14. John Smith

    John Smith Guest

    LOL ... talk about trolls! That HAS TO BE THE BEST TROLL OPENING LINE I
    HAVE EVER SEEN!
    Well, that is the second best ...
    hmmm ....
    Ever heard of amplifed rabbit ears?

    Regards,
    JS
     
  15. JB

    JB Guest

    Try a bowtie (like the one that came with sets) 5 inches in front of a piece
    of hardware cloth. Most of the boxes (which are almost free after the FCC
    rebate) have a signal strength bar (although with a 3-5 sec. delay)

    Years ago they used to make one as a magazine rack that you could pick up
    and move around.
     
  16. Hi John.
    It's not a troll. I bought a fair good UHF-VHF antenna,
    assembled it and sat it on a saw horse in the driveway
    for test, and it tested perfect for 3 channels + ch.34 .
    So I set her up using a roof mount and LOST ch.34,
    and no amount of rotating got it back.
    (I was a pro antenna/tower installer as a kid).

    Next I'm going to tape wire on 1/8" panelling and do
    experiments ... ugh, I hate trial and error.
    Ken
     

  17. Why don't you sell your house and move to a place next to the TV
    transmitter station. You will only need a piece of wire then.
    Or the bare finger.
    Must be wet, of course.


    w.
     
  18. Cecil Moore

    Cecil Moore Guest

    Here in the Tyler, TX area, the TV stations are continuing
    their analog broadcasts on their previous channels. Their
    digital signals are on different channels. When the switch-
    over comes, they plan to switch their digital channels over
    to their previous analog channels.
     
  19. Cecil Moore

    Cecil Moore Guest

    Some of the converter boxes have a signal strength
    indication. My "Insignia" box does. It allowed me
    to find a sweet spot for channel 10 DTV reception
    using RS rabbit ears.
     
  20. Cecil Moore

    Cecil Moore Guest

    I bought one, a Phillips MANT310/MNT310F - didn't work
    as well as the non-amplified RS one I already had.
     
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