RR_NDB,
We are addressing this within the AF447 frame work. The planes are normally heard adequately loud at DAKAR, judging from what I can hear from planes going out over the Pacific with a poor antenna on my receiver. If DAKAR experiences high noise levels THEN the transmit antenna efficiency makes a difference.
On receive if you can disconnect the antenna, replace it with a dummy load, and then observe a decrease in noise as heard in the speakers or on the signal strength meter, there is no improvement to the antenna that you can make that is meaningful. I know there is ham lore that says you gotta have a preamp on the receiver to get best results even at 160 meters. 'Tain't so, McGee. I've carefully tested it. And actually listening is easier with attenuation cranked in enough to lower the noise out of the speakers if the AGC is tuned right. (I doctored my R-390A to prove this. It has a VERY nice gain distribution in this regard.)
At frequencies above 14 MHz the antenna input impedance may become fairly high. But, come to think on it, the coupler elements should have little difficulty matching the higher impedance at a higher frequency. The circuit element value range needed is well within range of a tuner that can tune down to 3MHz.
Your second message prompts as reply that I am interested in your observation that a non-conductor can make an antenna. Your message is nonsense because the VS is fiberglass with little or no metal in sight, so far as I know.
Please do slow down and think first. (I know, I have the same problem.)