Found in old documentation, this circuit is tuned to pass signals below 245 Hz with a level of 0.044 dB above 500 Hz.
In the figure we have a Texas Instruments circuit for TTL interfacing using discrete transistors. The two...
This circuit was found in Radio Electronics magazine from June 1963. The range is small and the...
The project presented in a 2009 documentation is intended for radio amateurs operating in the...