# "Adding" Frequencies: 2 input mixer

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Matt Mauro, Apr 2, 2014.

1. ### Matt MauroNew Member

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Good evening all,

I am working on a project that requires the mixing of 2 separate AC signals. I have done a lot of research and have not found any helpful information on how I can "add" these frequencies to produce a new frequency. For example, if I have an input1 of 5khz, and an input 2 of 1khz, I would (ideally) like an output of 6khz. I am not sure if this is possible or not. Even if this new output was not the sum, but simply the difference, multiplication, ect, I would be happy. Can someone please help as soon as possible?!

Thanks!

2. ### magvitronActive Member

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Adding two wave forms of the same frequency may add up their amplitudes if they are in phase. But of two different frequencies, simple addition may result in a complex wave form not the added frequency. for that you need something like frequency multiplier.
PS you can generate one which is the sum of two by finding out the frequency of the 1st wave form and the other and synthesize the new wave form

3. ### ccurtisActive Member

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You can use a frequency mixer circuit, but the output waveform will be a combination of the sum and difference frequencies of the two inputs. You can then filter out the difference frequency component leaving only the sum frequency component remaining.

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5. ### misterTWell-Known MemberMost Helpful Member

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Frequency to voltage converter -> add dc voltages -> Voltage to frequency converter.

6. ### Nigel GoodwinSuper ModeratorMost Helpful Member

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As mentioned you need a frequency 'mixer' (not the same as an audio mixer), this gives you sum, difference, and the two originals - using a double balanced mixer will give you only sum and difference (you then filter the difference out).

However, as always with these vague questions you might do better to tell us exactly what you're trying to do?.

7. ### crutschowWell-Known MemberMost Helpful Member

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To get the sum of two frequencies you don't "add" them, you "multiply" them. At those frequencies an analog multiplier could be used to generate the sum and difference frequencies. You may need to add an output high-pass filter to filter out the difference frequency.

8. ### misterTWell-Known MemberMost Helpful Member

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So, is my idea impractical? I have not done much fancy analog circuits, but I know that FtoV and VtoF circuits and ICs do exist.

FtoV should be easy (within certain dynamic limits). Adding dc voltages should be easy. Then use something like AD654 for VtoF conversion. (+Some filtering if sine-wave is needed, or integrate to triangle and shape into sine)

Last edited: Apr 3, 2014
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9. ### Dick CappelsMember

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This done all the time in different ways for different purposes.

What are the signals you want to combine and for what purpose what do you want to do this?

Have a look:
http://en.wikipedia.org/wiki/Heterodyne

10. ### ccurtisActive Member

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Nah, I think it's a good idea, actually. It certainly has the advantage of performing the task if the input frequencies are variable, since a fixed filter would not work in that case. It's not going to be a perfect multiplication function, but then, the precision required is a matter of what the requirement is. The output response time to a changing input frequency will be relatively degraded, but then, that's also a requirement issue. A linear VCO can give a high quality sinusoid output from the summed DC voltages (scaled as may be necessary), in place of a V-to-F with filter.

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11. ### misterTWell-Known MemberMost Helpful Member

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When ETO members are more active solving the problem than OP