|Phasing harness for Yagi antennias - 144Mhz and
- . - . - - . - - . . . - . - - . . . . . . . . - . . . - . Jon Finley
|The phasing harness allows 2 or more yagis (beam antennia) to be co-phased
or bound together as if they were one single much larger antennia. By phasing 2
yagis together you can increase your forward gain by at least 3dB, increase your
front-to-back ratio and decrease your pattern width (narrow your beam).
Arrays are stacked based upon the yagi polarization. i.e. if the yagi is vertical the array is stacked horizontally (across from each other), or if the yagi is horizontal the array is stacked vertically (above the other). You'll hear them referred to as a "vertical phased array" or a "horizontal stacked array".
Well... to phase two antennia, you have to "feed" them out of phase. In addition, since you are also combining two 50 ohm antennia together into one, you have to deal with an impedance mis-match.
To solve the phase issue we feed the antennia with feed-line that is an odd number of quarter waves in length. The impedance is solved by using 75 ohm line.
The calculated total length of the phase line is cut in half, then assembled using standard connectors and a "T" connector. The "T" connector connects to your normal 50 ohm coaxial line.
Ideally, to get the most benefit from the phased array, the array members should be 1 wave length apart (this gives you the most forward gain, rejection and narrowest pattern). Holding this in mind, for 2 meters the shortest harness would be approx. 13 feet ( 6.5' + (3' ea. side) to reach each yagi's connector.
For Stacked array 50ohm ant. Use 75ohm RG11 or RG59
Length is measured from connector tip to connector tip with the 'T' connector in place (see below).
Calculate your phasing harness length for 144Mhz (2M) and 440Mhz