archive2009-14.pdxradio.com » Portland Radio

Way low power is different engineering than full power

(5 posts)
  • Started 8 years ago by kwvtsalem
  • Latest reply from Kent.Randles

  1. kwvtsalem
    Member

    I missed the comment early on about Low Power and referencing KPDX. KPDX was running just above the LPTV limit I think, and in Dallas and Salem it was coming in okay (not great) even at that power level. The problem is most Full power antenna design is set for 1/2 deg or 3/4 deg of beam tilt. The assumption is that the close population will get the signal just because they are close in. This is the reason I think KPDX was good in the mid valley (not great mind you) but was viewable unless there was a lot of rain or wind. When you design an antenna system for a LPTV it needs 3 or more deg of beam tilt if it is in town because you are NOT looking for the horizon you are looking for close in. Look at channel 5 (was channel 4 when I designed it) it had little gain (thereby a wide beam) and had a good reach into Portland even downtown. The other item that UHF can do because wavelength is so small, so they do it, is to make these antennas high gain that signal comes form somewhere and normally it is by reducing the beam width vertically I have seen antennas with only a 3 db point 2 deg wide.

    So it is not the power you have it is how you use.

    Posted on May 19, 2009 - 11:29 AM #
  2. Stephen
    Member

    Hey Ken...

    I was wondering if you had any recommendation for a decent antenna? I bought a Zenith ZHDTV1 and it's decent but it's no where near pulling in your signal from Beaverton (Kind of a geek that way). I can't place it on the top of the roof so any suggestions will help!

    Thanks!

    Posted on May 19, 2009 - 05:25 PM #
  3. jr_tech
    Member

    "Look at channel 5 (was channel 4 when I designed it) it had little gain (thereby a wide beam) and had a good reach into Portland even downtown."

    Is that the array with the circular reflectors that is about 2/3 the way up the new TV tower at the Sylvan site?

    Posted on May 19, 2009 - 07:55 PM #
  4. Andy_brown
    Member

    Very close in coverage is generally served by adding null fill to beam tilt, especially when located on mountains or tall towers, to prevent too much of the signal from overshooting the nearest part of intended coverage area.

    http://www.eriinc.com/pubs/WP22033.pdf

    Posted on May 20, 2009 - 10:30 AM #
  5. Kent.Randles
    Member

    Wasn't the original channel 4 antenna a Jampro CP panel?

    Posted on May 21, 2009 - 09:28 PM #