A Simplified Directional Facility (SDF) provides a final approach course similar to that of the ILS localizer although is not as precise as Localizer. It does not provide glide slope information.
The SDF transmits signals within the range of 108.10 to 111.95 MHz.
The approach techniques and procedures used in an SDF instrument approach are essentially the same as those employed in executing a standard localizer approach except the SDF course may not be aligned with the runway and the course may be wider, resulting in less precision.
Usable off-course indications are limited to 35 degrees either side of the course centreline. Instrument indications received beyond 35 degrees should be disregarded.
SDF is not explicitly mentioned in PANS-AIM. Hence, for the purpose of this coding guidelines the specific requirements are derived form those specified for the ILS in PANS-AIM.
...frequency,... zero bearing direction
In addtion PANS-AIM ENR 4.1. and also AD2.19/AD 3.18 require
for VOR, station declination to the nearest degree used for technical line-up of the aid
The diagram below shows the AIXM classes, including the relevant data types, needed to encode that information The main class is the VOR which is a specialisation of the NavaidEquipment.