Frequency adding.

[George Gosbee]

Hello all,

Is it easy or even possible to add 2 low level frequencies? i.e. if I have
3kHz and 1.5kHz outputs can they be
added to give 4.5kHz?

George.

 

[Robert Lacoste]

Hello all,

Is it easy or even possible to add 2 low level frequencies? i.e. if I have
3kHz and 1.5kHz outputs can they be
added to give 4.5kHz?

George.

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,

 

[George Gosbee]

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.

 

[[email protected]]

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.

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

 

[George Gosbee]

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.

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.

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

 

[Rene Tschaggelar]

Hello all,

Is it easy or even possible to add 2 low level frequencies? i.e. if I have
3kHz and 1.5kHz outputs can they be
added to give 4.5kHz?

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

 

[Bob Monsen]

Hello all,

Is it easy or even possible to add 2 low level frequencies? i.e. if I have
3kHz and 1.5kHz outputs can they be
added to give 4.5kHz?

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.

--
Regards,
Bob Monsen

"I cannot persuade myself that a beneficent and omnipotent God would
have designedly created parasitic wasps with the express intention of
their feeding within the living bodies of Caterpillars"
-- Charles Darwin

 

[Ken Smith]

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?

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