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Antenna for channel 36

Discussion in 'Electronic Design' started by Peabody, Nov 28, 2012.

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  1. Peabody

    Peabody Guest

    I need to bring in a distant TV station, and would like to build an
    antenna specifically for that channel. It's physically channel 36,
    which is 602-698 MHz, wavelengths of 49.8 - 49.3 cm.

    I just told you everything I know about antennas, and haven't had
    much luck on Google. I need it to be about 3-4 feet long, and it
    will be indoors. If anyone knows of a fairly simple design that
    might work, I would appreciate a link.

    I have a $10 indoor antenna, and it gets all the local channels,
    but not the distant one. The tuner shows the channel is there, but
    at low strength, and I'm hoping an antenna with the
    elements optimized for channel 36 will be enough to bring it in.
     
  2. Sylvia Else

    Sylvia Else Guest

    The Wikipedia article on Yagi antennas points to this document

    http://tf.nist.gov/timefreq/general/pdf/451.pdf

    indicating that the design is far from straightforward.

    I'd just get a normal rooftop UHF (band IV/V) wideband antenna, and see
    how well it works indoors.

    Sylvia.
     
  3. miso

    miso Guest

    The Blonder Tongue BTY-10-U is a high gain UHF antenna that spans a few
    channels. It is not cut for one channel, but you would get the one that
    spans channels 57 through 69. I have my doubt how well this will work
    indoors.

    Unless your time is 100% free, I'd get an antenna off the shelf. When
    you roll your own antennas, it is an exercise in material science. You
    can build out of aluminum, but there is always that nasty connection to
    copper. If you build out of copper, the thing is heavy. Plus copper
    isn't cheap.
     
  4. Peabody

    Peabody Guest

    Jeff Liebermann says...
    Yes, I've done that, and also confirmed with the station
    engineer that under normal conditions people in my area
    do get the channel. But in my particular case, I'm on the
    backside of a large hill with respect to the station's
    antenna, so I may just be blocked no matter what I do.

    I'm 35 miles from the antenna, but a friend of mine 10 miles
    farther out can get it ok. But he's out on the flat plains,
    and has a rooftop antenna.

    Remember the analog-to-digital transition? Well I got one
    of those voucher-paid converters, just in case, which I
    haven't used until now. It's a Zenith DTT901, and it can
    display a little signal-strength meter in real time. The
    local channels that I get just fine come it at about 70% on
    the meter, or close to that. It does detect channel 36, but
    at about 35%, and the tuner just can't make sense of it at
    that point - it doesn't even display the nominal channel
    number.

    But that's with a RCA ANT111, with just the basic single
    loop for UHF. So I thought with maybe a little better
    antenna, I might be able to receive the channel.

    I appreciate all the suggestions. I think I have enough
    information now to build a yagi. And with the wavelength
    being only about 1.6 feet, it shouldn't be that expensive.
    I have some twinlead, and a balun, and maybe even some
    copper wire that would work. It turns out that there is the
    right Blonder Tongue antenna on Ebay for $100 plus shipping,
    but, you know, I may learn something about antennas doing it
    myself.
    That was my thinking. If I build one for cheap, and the
    signal strengh is only marginally better, then it's unlikely
    even a good antenna would do the trick. But if I get major
    improvement, even if not quite good enough, then it may be
    worthwhile to build, or buy, something better performing.

    Just to clarify a couple things - it appears that the
    reflector and the directors are continuous elements - not
    cut in the middle, whereas the driven element is cut. Is
    that right? And does it matter where the twinlead is
    attached to the driven element - does it have to be at the
    inside ends?

    Thanks for all the comments and suggestions.
     
  5. amdx

    amdx Guest

    You're right Channel 36 is 602Mhz to 608Mhz.
    http://www.csgnetwork.com/tvfreqtable.html Mikek
     
  6. Mark Zenier

    Mark Zenier Guest


    There were plans for an easy to build four bay Hoverman on a website
    back a few years ago. This is a broadside array, not a boom antenna.
    But it's basically just some sticks, a couple lengths of bent wire,
    (and an optional screen if you want it to be unidirectional, instead
    of bidirectional). It will probably have as much gain as you can get
    with a convenient Yagi. This would be a low effort try just to see
    if more antenna will help.

    Somebody here in the newsgroup built it, try and see if google groups has
    the traffic (with the URL) from around the time of the digital conversion.
    Or google for terms like "UHF", "Four Bay", "Hoverman". I vaguely
    remember it as being on a Canadian web site.


    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
     
  7. Joerg

    Joerg Guest

    Once you get a Yagi going try pointing it in the opposite direction if
    you can't catch enough signal. May sound weird but sometimes it can pick
    up a station via reflection from a gutter or metal roof far away, from a
    house that can "see" the station.


    That <censored> transition was a major loss for us. Many evenings we can
    barely receive a single station, on account of multipath reception.

    [...]

    Yes, it has to be connected in the center.

    [...]
     
  8. Joerg

    Joerg Guest

    Probably could have glued it but told your wife it's beyond repair
    because you had already mentally repurposed the broomstick piece :)
     
  9. whit3rd

    whit3rd Guest

    I did this very thing a few decades ago, and would offer three more bits
    of info.

    First, the yagi design is very directional; find the correct bearing to your
    transmitter with (for instance) info from antennaweb.org.

    Second, long range transmission is limited by line-of-sight, and the curvature of the
    earth. Higher antennae see farther. If you can't get your antenna high, look for
    high items that act as reflectors (my best reception was with the antenna
    aimed at a nearby ham operator's high antenna mast).

    Third, lots of folk will suggest amplifiers; they do NOT GENERALLY HELP
    because your signal-strength limit is on signal/noise ratio, which is
    not improved by any addon amplifiers. Amplifiers amplify noise just like
    they amplify signal.
     
  10. tm

    tm Guest

    This is certainly not correct. The loss in the feed line adds directly to
    the noise figure. Put a LNA right at the antenna and you establish the
    system NF to that of the LNA.
     
  11. Guest

    Where are you living ? In Americas or the rest of the world ?

    Channel 36 with 602-608 MHz might suggest this is about America.
    In order to have any advantage of a "high gain" (=directional)
    antenna, you _must_ be able to use an outdoor antenna !!
    If you are limited to indoor antennas, there is no point in using long
    (directional) yagis, _unless_ you have a direct view from your window
    towards the transmission station.
     
  12. Guest

    Since the OP was not able to use an outdoor antenna, the issue of
    antenna amplifier gain or feeder losses are quite irrelevant.
     
  13. Joerg

    Joerg Guest

    Tell your boys that this is _not_ a baseball bat and also not for
    playing hockey :)
     
  14. Guest

    Or point the null to eliminate one source of multi-path.
    I probably should try OTA where I am now but there was no hope where I
    was before.
    Yes, the driven element of a yagi is a dipole.
    It is a dipole. ;-)
     
  15. Joerg

    Joerg Guest

    In our case there are many stations such as Fox-40 where there is no
    null. You always have tons of signal but sometimes the TV can't decipher
    any of it, other times it sorta works. 80-90% of the time, at the most.
    That was our "digital dividend" :-(

    DTV, what a joke. I think it means "disrupted television" or something.


    Other than evening news (which you can get on the web), some old movies
    (if you are lucky and the signal path holds for 2h) and Dancing with the
    Stars it's hardly worth it. In contrast to the election our favorite
    candidate won yesterday on Dancing with the Stars.


    Sometimes they are fed a bit off center to find a match compromise. My
    portable EMC antenna is like that.
     
  16. miso

    miso Guest

    If you found the BTY-10-U cut for your channel for $100, I'd get it.
    Worse comes to worse, you put it back on ebay. That price is about half
    of what Solid Signal charges.

    I only build antennas for what I can't buy. It is way more work than you
    think.

    If you don't want to buy the BT antenna, I would suggest building a
    biquad. They don't take long to build. You would probably have to scale
    a biquad designed for wifi.
    Your reflector would be Al screen rather than PCB at these dimensions.

    The thing with yagis or log periodics is that you need to align a lot of
    things for the magic to happen. The biquad doesn't have many critical
    dimensions.
     
  17. Joerg

    Joerg Guest

    Yup. But it backfired on the stations. This is a fairly affluent
    middle-class neighborhood and many people can't see much OTA TV anymore.
    Got miffed, pulled the plug. Now they get the news via Internet and the
    movies via Netflix. Guess what that does to the ad revenue of the stations.

    Until yesterday, that was the grand finale. My wife and I did a lot of
    ballroom dancing so we always thoroughly enjoy that. And ok, the hi-res
    is nice for such events. If the signal holds, that is.

    Now you know why we have neither cable nor satellite TV.
     
  18. Peabody

    Peabody Guest

    says...
    Well, that brings up the issue of what kind of dipole. From
    what I've read, using a folded dipole as the driven element
    has two advantages - it provides a broader bandwidth (which
    isn't really important in my case because I only need one
    channel), and it provides a better match to a standard
    300/75 balun. Apparently a simple dipole presents matching
    problems, although to tell you the truth I don't understand
    why.

    I found a video on Youtube which looks like a good example
    for me to duplicate - adjusted a bit for the difference in
    frequency. It's a 6-element Yagi which uses a folded
    dipole:



    Of course this is an Aussie design, so I'll probably have to
    turn it upside down.
     
  19. amdx

    amdx Guest

    Would it be possible to connect two antennas 180* out of phase then
    find a couple of happy directions to cancel a portion of multi-path of
    the Fox-40 signal.
    Just a thought.
    Mikek
     
  20. tm

    tm Guest

    I think the connections between the top and bottom dipoles need to cross
    over.
     
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