I wish to check dial of my signal generator for accuracy at 600-kc.
Shown in simulator, left signal generator 605-kc output signal is radio frequency only with no modulation, coupled from signal generator through 250 pf (600 volt rating) capacitor to antenna input of AM receiver radio. Right signal is AM receiver radio tuned to a modulated commercial broadcast at 600-kc. Both signal generator and AM receiver are grounded to each other as well as a good common ground connection.
The simulator is showing whistle we would hear of 605-kc minus 600-kc = 5 kc (beat note). At 5000 hertz we hear whistle sound out AM radio speaker.
As I adjust signal generator closer to match AM frequency the pitch of whistle becomes lower and when the frequency is close the beat note sound will disappear (zero beat). If I continue to adjust signal generator in same direction the beat note sounds will appear again.
Now, I want 600-kc on signal generator and area AM broadcast stations closest to 600-kc are 570-kc and 660-kc.
First, zero beat with 570-kc radio station. Signal generator reads 560-kc on dial. We are 10-kc low so set signal generator to 590-kc for 600-kc signal desired. To verify, zero beat upper 660-kc station to make sure we read 650-kc on signal generator dial.
