A recent discussion on the 147.210 MHz.WB6LFC repeater brought to bear this question. "What side of the "Q-line" of a "J" antenna does the center conductor of the coaxial transmission line have to be connected and why"? The person who asked this question offered that he had seen in certain antenna publications that, "it doesn't matter"! The response answer given was, "it matters if your not going to feed it as a balanced termination, either with a balun, or with balanced transmission line". The reason for this answer is of course that the parallel conductors of the antenna's "Linear Impedance Matching Transformer" provide for balanced currents of equal and opposite phase. So here we are again, discussing the nature of one of the most popular VHF antennas to grace the Ham bands in the last couple decades. To this end the offer was made, "we have the means, and the technology to put this to a test"!

So, how would this test be conducted? First we must state the question or questions to be answered. These questions are:

Is the radiation efficiency of a halfwavelength "J" antenna effected by feeding it with an unbalanced transmission line dependent on whether that transmission line's center conductor is connected to the side of the Q-line that is directly attached to the radiating element? Or, can equal signal performance be attained no matter which side of the Q-line is connected to the coax cable's center conductor?

I should state at this time that one of the statements that was made by one of the "round table" discussion participants was, "it can't make any difference because I can get a good SWR match no matter which way the antenna is connected". The answer to this statement was, as you might guess, antenna impedance matching is not a criterion that would determine this answer! Mike AC6SX, who was part of this discussion offered, "a properly tuned Q-line linear impedance matching transformer would display a good SWR, even if no antenna load was attached to it!". This would not of course though provide a good and efficient antenna!

So, here is the outline for testing that I would propose take place at our antenna test range:

1. Provide a model "J" antenna adjudged to be a good performer. This antenna "standard" should be fabricated in such a way that its coaxial cable connections can be easily reversed!
   
   
2. I would also suggest that a simple Q-line transformer be fabricated to test Mike's statement, and that of course "signal performance data" should be taken and recorded for both of these "test fixtures" for later assessment and publication!
   
   
3. I would also offer that to better validate the test, that the transmission line be kept perpendicular to the test fixtures, and
   
   
4. that an "RF Choke" be provided near the fixture's "feed-point" to further reduce signal radiation on the coaxial cable's shield!

Now all we need to do is sort out who in our group is going to provide the necessary equipment and hardware to perform these tests, and when we are going to travel to our desert dry lake antenna test area to perform the tests?

I might offer as an adjunct to this that maybe we could include some of the 6 Meter band antenna tests that have been recently discussed. I offer this as only a side thought as it would markedly increase the amount of hardware that would have to be assembled.