In both Boeing and Airbus airplanes there is one HF antenna shared between 2 HF transceivers. It is located just behind the leading edge of the Vertical Stabiliser.
There are 2 other components between the HF transceivers and the antenna. One is a coupler that connects the transmitting HF to the antenna. The other is an antenna tuner that optimises the antenna to the transmitting frquency.
While only one HF is able to transmit at a time, both HFs are able to receive simultaneously.
You are correct. The physical antenna is about a metre long.