The regenerative system was highly non-linear, amplifying any signal above a certain threshold by a huge amount, sometimes so large it caused it to turn into a transmitter (which was the entire basis of the original IFF system). In RDF, the strength of the signal is used to determine the location of the transmitter, so one requires linear amplification to allow the strength of the original signal, often very weak, to be accurately measured.
The regenerative system was highly non-linear, amplifying any signal above a certain threshold by a huge amount sometimes so large it caused it to turn into a transmitter (which was the entire basis of the original IFF system). In RDF, the strength of the signal is used to determine the location of the tr,ansmitter, so one requires linear amplification to allow the strength of the original signal, often very weak, to be accurately measured.