This circuit is from an old publication from 1973, intended to measure signals in the range of 40 meters from radio amateurs. The coil L1 has 5 turns and L2 30 turns of wire 22 in a ferrite core. The transistor can be BC558 and the germanium diode can be 1N34. The coil can be modified for operation in other ranges. The antenna is 7-inch telescopic.
