# How is the frequency multiplied by four here?

Since I don't have all the parts, I modified the circuit diagram:

I have edited this circuit diagram.

When I add the Zener the sound improved. The Zener is a 1N4742 (between crystal and inductor to ground.)

Circuit shown in the YouTube video

What I don't understand is how the 25 MHz frequency became 100 MHz. Also I can hear a blank sound in 100 MHz tune in (digital) radio. The 20 nf capacitor is there to get output. I am not sure if it is the output. Notice that the inductor and capacitor (near collector) are completely irrelevant as shown in the video.

According to the equation,

$$\R = 1/(2πFC) \$$

20 nf capacitor should be enough to pass 100 MHz wave.

• Do you know what harmonics are? Jul 12, 2021 at 5:49
• No I am just a electronic hobbyist. Jul 12, 2021 at 5:50
• Adding a zener is probably not a good idea as it has significant capacitance and you’ve put it in the rf path. The inductor in series with the crystal is to make it oscillate on a harmonic. Jul 12, 2021 at 6:18
• @Kartman the zener may be acting as a varicap to pull the crystal slightly and produce deviation based on the audio input - a crude FM modulator.
– user16324
Jul 12, 2021 at 10:32
• In your spare time watch a few videos on basic electronics. They probably will not answer your question but you will better understand the answers we give you.
– Gil
Jul 12, 2021 at 19:43