This circuit oscillates in the fifth harmonic of the crystal frequency. The circuit is from a 90's documentation. L1 must be according to the desired frequency.
This simple operational amplifier tester was published in the November 1987 issue of Radio...
This squelch or silencer for receivers for the 11-meter band was found in the November 1971 issue...
This reader with TTL logic compatible output uses an LM139 comparator. The circuit was found in...