Arnaud, all,
Trying to reduce the confusion a bit, let me again summarize the different radio sets as used by the RAF by May 1940.
- The basic set for all bombers was the TRF General Purose radio, consisting of the R1082 and T1083. This set operated at low frequency, so large range, and was intended for communication of the individual a/c with their base. With a rotatable antenna it could be used for direction finding. As far as I know this set was NOT used for a/c to a/c communication.
- For fighters there was the TR9D, consisting of the R1120 and T1119, operating at 4.4-6 MHz. Range of this set was very poor, and was useless a few km away from the air field. So it could then only be used for a/c to a/c communication.
- Around May new fighter a/c were started to be equiped with the much better TR1133 set. I expect that not many units in France already used this radio, probably only home based Fighter Command a/c.
- Coastal Command used a simplified version of the TR9D, the TR9J
- The TR9F was installed into bombers probably from the end of 1940, adding a 2nd channel and possibly a/c to a/ccommunication. So it is pretty impossible to find TR9F in May 1940 a/c.
So yes, from that perspective I'm still surprised you've found a Battle with a TR9D. The question is whether it still contained the standard TRF, with an additional TR9D, or had the first one replace with a TR9D. The best explanation is that Battle pilots valued a/c to a/c communication more than communication back to base, and installed the standard fighter equipment.
Regards, Pieter