Re: Vor V-Shaped Tail Antenna Physics
Posted: Wed Jul 18, 2018 3:25 pm
Gary,
I'll try to explain. As mentioned in the beginning of this message stream, the the purpose of the Balun is to help electrically match the antenna (which is a balance load because both sides are the same) to the coax cable (which is not a balanced load). The name "Balun" is the two words "Balanced" and "UnBalanced" combined to make one word. The idea of using a Balun on the airplane is that the net effect is that it helps the antenna receive better in all directions when mounted on the airplane. IS THIS REALLY NEEDED?? Probably not if using a newer solid state radio because the VOR receivers are normally more than sensitive enough to pick up signals while in the air but if using an older radio, the Balun might be needed to give the radio a little higher signal strength in all directions.
So how does the Balun do its job? On the antenna side of the Balun (Balanced section) the two leads are driven 180 degrees apart by the loop section of the Balun. The loop is 1/4 wave down and then 1/4 wave up to give a total delay (phase rotation) of 1/2 wave (or 180 degrees). The actual physical length of the loop is reduced by about 20% because the signals inside of the coax are slowed down by that much. The net effect acts sort of like a transformer in that the unbalanced coax cable coming from the radio is transformed from a unbalanced load to a balanced load and one side is rotated 180 degrees and then connected to the antenna. If I had a blackboard and you where here, I think I could do a much better job of explaining. By the way, I think in your 3rd drawing, there is a type-o. I am not sure the 3rd drawing would work. I used the 4th drawing because that was what was in the airplane originally and it is easier to make because you do not have to solder at the bottom of the loop.
Jim Collins
I'll try to explain. As mentioned in the beginning of this message stream, the the purpose of the Balun is to help electrically match the antenna (which is a balance load because both sides are the same) to the coax cable (which is not a balanced load). The name "Balun" is the two words "Balanced" and "UnBalanced" combined to make one word. The idea of using a Balun on the airplane is that the net effect is that it helps the antenna receive better in all directions when mounted on the airplane. IS THIS REALLY NEEDED?? Probably not if using a newer solid state radio because the VOR receivers are normally more than sensitive enough to pick up signals while in the air but if using an older radio, the Balun might be needed to give the radio a little higher signal strength in all directions.
So how does the Balun do its job? On the antenna side of the Balun (Balanced section) the two leads are driven 180 degrees apart by the loop section of the Balun. The loop is 1/4 wave down and then 1/4 wave up to give a total delay (phase rotation) of 1/2 wave (or 180 degrees). The actual physical length of the loop is reduced by about 20% because the signals inside of the coax are slowed down by that much. The net effect acts sort of like a transformer in that the unbalanced coax cable coming from the radio is transformed from a unbalanced load to a balanced load and one side is rotated 180 degrees and then connected to the antenna. If I had a blackboard and you where here, I think I could do a much better job of explaining. By the way, I think in your 3rd drawing, there is a type-o. I am not sure the 3rd drawing would work. I used the 4th drawing because that was what was in the airplane originally and it is easier to make because you do not have to solder at the bottom of the loop.
Jim Collins