VDF and QGH approaches were significantly different.
With a VDF approach, the pilot was issued with a series of QDRs which was interpreted (using the appropriate letdown plate) by the pilot to decide his/her position in relation to the airfield.
With a QGH approach (latterly called CDTC - Controlled Descent Through Cloud) the pilot is instructed to fly a series of QDMs and is instructed when to descend by the controller and it is thus classed as a type of Ground Controlled Approach.
With VDF being mainly at civil airports and QGH being mainly military (one exception was Goodwood before it became AFIS), the QGH was often designed to get the aircraft within the scan of the PAR.
Both types of approach require similar equipment ie some sort of direction finder display which automatically provided a bearing whenever the pilot transmitted either on a VHF or UHF frequency.
This was not available during WW2 as far as I'm aware; the only D/F systems being 'homers' whereby an operator on the ground manually turned the receiving aerial (a loop antenna) until he/she received a minimum strength signal. The bearing was then read off a calibration ring and passed to the pilot.
Sometimes the 'homers' were positioned in a pattern of 3 receiving stations so that the exact aircraft position could be plotted fron the 3 bearings, the three for Farnborough being at Cove, Medstead and Twinwoods Farm.
Additionally, some airfields were equipped with SBA or 'Standard Beam Approach' which worked in a similar fashion to ILS but with the pilot judging his position by hearing a series of dots when he was one side of the localiser or dashes when the other side, with a continuous note when he was on centreline rather than having a dial to refer to
Last edited by chevvron; 7th Oct 2016 at 11:25.