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  1. #1

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    Questions concerning broadcast antennas for 88.1 thru 107.9 MHz

    I have created this thread to ask a few questions about antennas for broadcasting in the 88.1 thru 107.9Mhz broadcast band in the USA.

    First, which antenna is better for distance when the terrain around the antenna site contains a higher elevation and large buildings? A vertical dipole or a vertical 1/4 wave ground plain?

    Also, if a two bay vertical dipole was constructed, what formula exactly, is used for the bay spacing? I have always seen these antenna setups with two or more bays, but never seen any type of spacing requirements listed.

    Third question. Antennas are either vertically or horizontally polarized, is there an antenna setup that covers both?

    I am curious If a 4 bay antenna setup was constructed, can they be phased so that they are from top to bottom vertical, horizontal, horizontal, vertical?

    Also is this antenna (pictured below) considered a vertically and horizontally polarized radiator? And how are these wired to the feed line? Are they separate elements, with the hot and shield attached to each (which is hidden from view)?


    Thanks in advance... Bruce.

    ANTENNA.jpg

  2. #2
    andhow's Avatar
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  3. #3
    saint's Avatar
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    The type of antenna will be dictated by the final RF power used. If you going with a part 15 transmitter - you would need several directional antenna's connected to several transmitters to achieve an "extended" signal foot print.

  4. #4

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    bruce

    the "gain" on a bay antenna is doen by "frequency spacing" for example our station uses a 7 bay array, and we have a 100kw signal, i think our main harris tx is only 14 kw though, so stacking gives us the push

    if you are tx ing from an area with high buildings you will need MORE "RF" to "punch" through the buildings, outside they will hear you everywhere but inside you will have no signal received, this is the law of RF and line of sight, very interesting stuff

    we once took a 1 watt pll and a antenna (single dipole) and on a clear "line" pushed it to 10 miles before signal dropoff

    have fun and do the engineering research

    also keep in mind that dipole and ground plane will have different "fresnal radiation patterns"
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