JD-EE
Inefficient and ineffective are two different ballgames.
Iīll use this to say you:
IMO a/c HF antennas could be more effective. Signals from ground stations would "better trigger" a/c receivers SELCAL; Signals from a/c would "better jump" over squelch thresholds of ground station receivers and crew could better communicate when VHF is out of range.
The efficiency of a C47, L1049, C130 (old versions) antennas were better than the "jet age" solutions.
Who compare? Old crews are retired and younger crews didnīt use older solutions.
I had the privilege to hear BOTH types and the difference is clear to me!
The antenna matching elements are not that bad.
We are talking about antennas and NOT ATUīs!
And efficiency of an antenna can be itīs capability to deliver a good signal to the back of your a/c. Itīs not related to "thermal effects".
On transmit it matters a little
Negative! This can be very important in certain situations!
Remember the "Threshold effect" in FM. We can think in an analogy when the ground station is under local QRN, etc. May be the difference in receive or lost the a/c call.
And every pilot know how difficult is HF in many situations. And always you can blame MUF, "propagation condition", noise, etc.
With better antennas at a/c and ground stations this could be completely different.
IMO the jet age, the SAT availability and other factors will not mention now reduced the "effectiveness" of a very good and reliable way of comm, the HF.
I believe the HF antenna is in the leading edge of the "plastic" vertical stabilizer.
FYI, this is not the antenna. Is just the element to "feed RF" to the VS. The other way (the DUAL) would be to "lift electrically)" the VS (through a china insulator) and feed the base of the VS with an ATU (L and C).
Very good engineers (mentioned by Graybeard 26th Apr 2011, 10:18) worked and invented adequate solutions.
Matching might get "dicey" at frequencies near 14 MHz
Voltage feed like in Zepp is "out of question" IMO in a modern airliner.
To be continued by editing.