A multi-purpose signal generator circuit

....The circuit is as shown in the figure. IC1 and C1 form a low-frequency oscillator of about 400HZ; IC2 and C3 form a high-frequency oscillator of about 37MHZ; the low-frequency signal output by C2 modulates the high-frequency signal. C4 and the antenna constitute the transmitting system. The harmonics of the high-frequency oscillator can be received on the third channel of the TV (or other channels) and display black and white bar signals. The output signals at point A and point B are used as detection signal sources for low frequency and image channels respectively. Replacing C3 with a quartz crystal can stabilize the oscillation frequency, as shown in the dotted line in the figure. If a pair of binding posts or sockets are used to connect C3, and C3 is replaced by a crystal respectively; the frequency is selected as 465KHZ, 10.7KHZ, 6.5KHZ, 4.43MHZ, 37MHZ, it can be used as an intermediate frequency signal source for radio recorders and televisions.