This traditional configuration found in a Radio Shack document can use 2N2646. More keys can be added, and the power can be supplied with voltages from 9 to 15 V.
Found in Exar documentation from the 1980s, this circuit has a 60 dB cutoff at 1800 Hz. The...
We found this circuit in the February 1984 issue of Radio Electronics magazine. It uses an...
In the figure we show how to use a varicap to modulate a signal in frequency. The circuit can be...