De PA0SNY/AM explanation page
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(Deze pagina is dus niet in het Frans of Duits)

Some details of HF on the A330 (747 is similar)

The purpose of this page is to give some background on the HF equipment installation
on the Airbus A330. I will not go into deep details, but will try keep it simple yet informative.

Basically the A330 has 2 HF systems, each consisting of an HF transceiver. This is the
Rockwell Collins model HFS-900 with p/n 822-0330-020.

Both transceivers are mounted in the avionics compartment, an area just forward of the forward cargo compartment.

The HF transceivers are controled from the cockpit. From three so called RMP's.
These are the Radio Management Panels. From these panels the 'radio' is selected
(HF1 or HF2) and the desired frequency is selected in the 'standby' window. After
that this frequency is transfered to the 'active' window. When pressing the PTT on
the microphone, the antenna coupler matches the transceiver output to the antenna.

From the Avionics Compartment, 52 ohm coaxial cabels run to the tail of the aircraft. On the lower part of the vertical tailplane, the HF antenna is mounted on isolating studs on the front spar, behind a composite nose.

The output of each antenna coupler goes directly to a piece of metal: the exiting plate.

	Here a pictorial display of the approximate location of the couplers and the exiting plate, here mentioned 'antenna'. In fact the coupler provides low voltage / high current RF to this plate, which in fact makes the vertical tail or even the entaire aircraft as an antenna. The wing tips on older 747's and the probe on even older 707 vertical fin, have the same principle.
The direct coupling of the two couplers is here well visible. The connecting cable from the coupler  (at the lower side if this picture) is fixed on the isolating stud mechanically, and attaches to the metal piece that we now know as 'the exiting plate' that is fixed to the vertical tail structure
	The situation on the tail's front spar: the whole exiting plate. The length is around three and a half meters (so 10 feet) only Note: on the 747 classic it is the stick in the wingtip! Same size.   The system can be 'tuned' over the range of the system: 3.0 untill 24 MHz This is less than what the transceiver can cover (up to 30 MHz) Also note that the transceiver can provide both USB and LSB, but USB is the only mode that can be selected (aviation standard!)

And finally an overview of the HF system. You see here the 'essentials' of the systems.