# Frequency doubler for sine wave

Discussion in 'The Projects Forum' started by paw1, Jan 13, 2015.

1. ### paw1 Thread Starter Member

Jan 13, 2015
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Hello people.

I'm working on a project where the goal is to build a frequency doubler. The input signal will be a sine wave that sweeps between 100 - 200 MHz. The output should be a sine wave that sweeps between 200 - 400 MHz.

I've found several frequency doubling circuits online (and in books), but the problem is:
1. the output isn't sinusoidal, or
2. I can't get them to work in simulation (LTspice IV - could be user mistake of course)

One big problem is that the circuits I find aren't complimented by an explanation on how to calculate the component values.

If anyone has suggestions for circuits, please, don't be shy.

Thanks

2. ### MikeML AAC Fanatic!

Oct 2, 2009
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I cant see how you could do this without a tracking oscillator using a sine-wave output VCO whose frequency is controlled by a phase-locked loop.

3. ### alfacliff Well-Known Member

Dec 13, 2013
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if you put a diode or other non linear device between two tuned circuits, thee first at the input frequency and the second at the output frequency, the diode will generate harmonics. keeping things sinusoidial on the output will require tuning a resonant circuit for flywheel effect.

4. ### GopherT AAC Fanatic!

Nov 23, 2012
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The guitar effects pedal guys simply make a full wave rectifier, filter extensively to round out the bottom peak and then amplify. There is some distortion but, hey, that is what electric guitar is all about.

5. ### MikeML AAC Fanatic!

Oct 2, 2009
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At 200MegaHz?

6. ### MrChips Moderator

Oct 2, 2009
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As Mike says, you need a PLL, phase-locked loop.

7. ### paw1 Thread Starter Member

Jan 13, 2015
32
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And, I forgot to mention, the circuit should be made up of all discrete parts (no ICs).

Thank you so much for your suggestions, although I don't have any experience with any of them. It sounds like this is going to be complicated

Forcing a transistor to clip should produce 2nd harmonics, right? What about doing that and filter out unwanted frequencies? Still clinging to the hope that this can be done in a relatively non-complicated way.

8. ### paw1 Thread Starter Member

Jan 13, 2015
32
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Thanks. I'll look into it.

9. ### wayneh Expert

Sep 9, 2010
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Says who? I trump them and declare that the circuit should not contain any discrete parts.

10. ### alfacliff Well-Known Member

Dec 13, 2013
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then step up the voltage, and jump a spark, it is rich in harmonics.

11. ### MikeML AAC Fanatic!

Oct 2, 2009
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Yes, but you requested a sine-wave, harmonic free, output. It is easy to make a frequency doubler at a single VhF frequency, where you can put an LC tuned circuit at the output tuned to the second harmonic of the input. It is a different matter entirely to make something that produces a clean sine wave at any frequency between 100 and 200Mhz.

12. ### GopherT AAC Fanatic!

Nov 23, 2012
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Ok, so I missed the M in megahertz. Sorry for the confusion.

Apr 5, 2008
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Hello,

Here I got some ideas from a german magazine (FUNK-AMATEUR, I translated the text):

Bertus

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14. ### paw1 Thread Starter Member

Jan 13, 2015
32
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I see.

Been looking into PLLs this evening, and it seems to be all good, but I'm unsure if it can stay locked unto a signal sweeping over a 100 MHz range (can it?).
Also, do VCOs output sine waves?

By the way, I may have misunderstood about only being able to use discrete components. I'll have to make sure.

P.S.: What are the boxes?

15. ### paw1 Thread Starter Member

Jan 13, 2015
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Hey, you tried to help. Appreciate it!

Apr 5, 2008
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Hello,

The boxes are mixer modules.
These can be ring mixers with buffers on the inputs.

Bertus

Oct 2, 2009
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18. ### Lestraveled Well-Known Member

May 19, 2014
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Wait a minute....Harmonic free??......... Nothing is harmonic free. The spectrum of a sine wave is composed of only even harmonics. The spectrum of a square wave is composed of odd harmonics. The shape of the fundamental wave predicts the spectral content and visa versa. Saying you want a sine wave, means you want the spectral content to be rich in even harmonics.

Why do you need a sine wave?

19. ### GopherT AAC Fanatic!

Nov 23, 2012
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I'll bet 10 op amps that your last question is not answered by the OP (or, if it is addressed, the answer won't make sense).

20. ### MrChips Moderator

Oct 2, 2009
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Not quite sure where you're coming from. I thought that a sine wave had only one frequency, the fundamental.