Ron H said:If you can handle AC coupling for your modulating signal, this should work down to around 20Hz.
I have used 1496's (many years ago). The modification I posted should work for that range.epilot said:Thanks Ron for your reply,
i want to give the IC a 40kHz as a carrier and a 50Hz to 15kHz signal as modulating signal.
today i spent alot of my time to find a solution for pin 14 of 1496 and a good matched carrier oscillator but there was no success with google!
don't know why there is no solution from IC company!
epilot said:Thanks Ron for your reply,
i want to give the IC a 40kHz as a carrier and a 50Hz to 15kHz signal as modulating signal.
today i spent alot of my time to find a solution for pin 14 of 1496 and a good matched carrier oscillator but there was no success with google!
don't know why there is no solution from IC company!
Nigel Goodwin said:From this, are we to assume you're wanting to send audio via an AM modulated ultrasonic carrier?, perhaps super-imposed on an IR LED?.
If so?, a 1496 seems rather overkill!.
epilot said:Hello Nigel, yes i want to modulate part of audio frequency with a carrier(i prefer 40kHz as carrier)
i can not understand you by "super-imposed on an IR LED"
i am working on 1496 and if i can nopt handle it i'll go for AD633 chip.
i'll try Rons way at first and see what will happen.
i lke to know what will happen if the carrier becomes a square wave
Nigel Goodwin said:Just that IR is often modulated at 38/40KHz, presumably as a left over from the old ultra-sonic days - so you may have been doing either.
I wouldn't expect it to make any difference to the modulation, my main concern is the entire premise of the scheme! - I suspect quality is going to be very poor, and your frequency range is highly optimistic.
What exactly are you trying to do?, and over what range?.
Ron H said:You don't need a sine wave. You only need about 500mV p-p for the carrier, but make sure it is SQUARE (50% duty cycle). You can get 50% from a 555, but not with the "standard" astable circuit.
The modulating signal (audio) will be clipped if you exceed 2V p-p. You should keep it below 1V p-p for low harmonic distortion. (Note: This applies to the balanced modulator.) You can play with making the resistor between pins 2 and 3 larger - maybe 2k to 3k. This will lower the audio gain, but will give you more dynamic range and linearity.
Also - and this is a biggie - this circuit is a balanced modulator,as designed. It just dawned on me that you want an amplitude modulator. See the schematic below.
Ron H said:An ultrasonic transducer has a fairly sharp resonant peak, so it can easily be driven by a modulated square wave. Even if you were using it as an RF modulator (e.g., for an AM transmitter), you could use a lowpass or bandpass filter on the output of the modulator to eliminate the harmonics of the square wave. In fact, a 0.5V p-p sine wave carrier input will overdrive the carrier switches to the point that you will essentially get square wave carrier output anyway.
I just realized that, with a 40kHz carrier, you should change the 51 ohm resistor to 470 ohms. I will edit the schematic to reflect this change.
Since the input impedance of the amplitude modulator is 470 ohms, you can attenuate the 555 output with a series resistor. For example, if you have a 12V p-p output from your 555, you can simply add a series 12k resistor and get approximately 0.5V p-p into the modulator
You don't need single sideband for an ultrasonic transducer. See https://en.wikipedia.org/wiki/Single_sideband
.
epilot said:by the way i think i must modify your first circuit to the second,
but what about an AM with a single sideband?
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