We found this circuit in an English publication in 1979. The diode should preferably be germanium and Q1 can be a BF245 or MPF102. The antenna is telescopic and XRF depends on the frequency, typically between 100 uH and 1 mH. The supply is made with 9 V and the zero setting is a 47k trimpot. The indicator is a 100 to 200 uA full-scale microammeter.