Frequency adding.

"George Gosbee" a écrit dans le message de news: rqkCf.19294$ snipped-for-privacy@fe1.news.blueyonder.co.uk...

You just need a mixer : Multiply the two input signals (at these frequencies an operationnal amplifier or a transistor will do it), you will get as an output the sum of (3-1,5)=1,5KHz and (3+1,5)=4,5KHz, plus some other mixing signals if the multiplier is not perfect. Why ? Just because cos(A)xcos(B)=1/2 x ( cos(A+B)à+cos(A-B)). Then you just need to pass your signal through a 4,5KHz band pass filter and you have your desired signal.

Cheers,

Thanks for the quick reply, I should have said variable signal i.e. 0.3 kHz to 7.5 kHz with the second signal always half of that. Do I just forget the filter to do this?

George.

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No, you need a tracking filter, it gets a whole lot more complex

Have now solved the original problem with 3 diodes and 1 resistor see, Header -- LPG ecu diode sketch -- in, alt.binaries.schematics.

Thanks for all the help everyone and the lpg now works ok just a little fine tuning to do.

George.

George Gosbee wrote:

No, you need a tracking filter, it gets a whole lot more complex

Yes, a single side band (SSB) mixer does that, moreless. You can add a sideband to a carrier. The carrier and the other sideband are not fully suppressed, though. Depending on the frequency range, the carrier and the other sideband are suppressed 20 dB, 40dB, whatever.

Rene

You can add them by using an FtoV chip on both inputs, adding the resulting voltages, and using a VtoF on the output. This works over a large range of frequencies. If you want to add a constant frequency, you just offset the input to the VtoF with a constant bias voltage.

In article , George Gosbee wrote: [....]

Throw away one of the frequencies and use a PLL on the other.