Top circuit is radio receiver tuned to one of WWV or NIST frequency standards.
Bottom circuit is device we want to check frequency or calibrate to proper setting.
Using two probes with two channel oscilloscope display the idea was to set bottom circuit closer to standard above than can be done with zero beating two frequencies.
Sound card in my smart phone seems to be limiting device as square waves have ringing waveform to sudden frequency changes and tick pulse of WWV does not display sharply as standard on above circuit.
Later, I will see how Virgins Sound Card Oscilloscope Probe does as signal input device. So far, square waves from software on tablet has been distorted on smartphone smart scope display.
Probe has three step attenuator rated for 24 volts + or - with protective circuit of 3 volts input limits if not over 24 volt range.
I hope to use with breadboard circuits as I learn more about sound card display range.
