Omni Antenna Actually Semi-Directional

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ridgescan

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wasn't there some conversations in here about this? Well I improved my peninsula agencies from western SF 2 bars on the meter by spinning the d130j antenna so that the 10' mast it's side-mounted to is behind it in relation to the direction of those agencies. Back to the roof to tighten everything up:) Wow-go figure:rolleyes:
 

nd5y

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If the antenna is mounted on a horizontal arm attached to a vertical mast you are moving the antenna around in a circle.
The higher the frequency shorter the wavelength gets so the greater the distance the antenna appears to move in relation to wavelength. You only need to move 1/4 wavelength to go from a peak to a null. 1/4 wavelength is only 20" at VHF high band down to 3" at 900 MHz so you don't need to move the antenna that far to see effects on weaker signals. The same thing happens when you move a hand held around or drive a vehicle.
If you kept the antenna in the center of the circle and rotated the mast around the antenna you would not notice as much difference.

A certain manufacturer advertizes that their cheap omni scanner antenna acts like a yagi when you rotate it around the mast like that.
I don't buy it. I would like to see somebody test it properly on an antenna range or at least with antenna modeling software to see how much directivity it really has.
 
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ridgescan

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Tom-thanks for making it so comprehendable. Good info. So true with regards to the hanheld example-my little pro-62 will actually receive all those agencies with good voice copy off the dukkie..IF you place it in the bathroom on the sink counter, 3 tiles from the edge:D or in the kitchen on top of the fridge 1 inch from the hinge lol
 
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