Yes, you can see the DF loop. I don't know when NDBs were introduced (non-directional beacons) but the loop in that dome would have been used for getting a QDM. That was a bearing from a ground station, and therefore a heading to steer to get back home. Or, if you had three bearings from different stations you could work out your position. My original question was because I didn't know that radio trainer Proctors had them, until seeing that fine photo of NP229.
Laurence