MC1496

Have you got the correct signal levels for the carrier and modulating signal inputs to the MC1496?

Leon

here are the pics of MC1496 and carrier oscillator circuitry

both use a 12V single supply

the melody is generated by an UM66 musical IC that i connected its output to "Vs" via a 22K resistor.

this is my first design in AM modulation with 1496 so i need for help please. by the way, what about a sine wave oscillator as a carrier??!

Mohammad, AM produces upper ans lower sidebands. So to start with replace the melody by a simple sine generator of say 1kHz.

Rene

yes it produces upper and lower sidbands, but what is the problem in the circuit?

if the circuit works just fine, there is no difference if i use a melody or a sine wave as modulated signal!

But have you checked the amplitudes of the carrier and modulating signal against the recommended values in the MC1496 data sheet? If they are wrong it won't work properly.

Sine waves are usually used, but mixers like that can often work from square waves. Check the data sheet.

Leon

Don't know yet.

The signals on the scope are simpler to interprete.

Rene

There may not be a problem, if you hooked up the 1496 per the data sheet, you are generating a double sideband suppressed carrier signal. How do you propose listening to it? An AM receiver won't work. Your carrier is too unstable to use an SSB receiver. You need to inject carrier into the output to get an AM signal; or, forget the 1496 and use a 2N2222 or the like, running class C, and amplitude modulate the collector. You could use a voltage regulator (not 3 terminal) as the modulator, and run your audio with DC bias into its reference input.

Tam

i have shown the circuit and think that it is per data sheet, is not it?

well, i have a project by ultrasonic , i have to modulate a signal(melody) with a carrier and send it via a ultrasonic sensor(40kHz) then i have to bulid a circuit as a receiver to get that signals from ultrasonic sensor with a R type of ultrasonic sensor and demodulate it and propagate it via a speaker.

i have built the modulator with 1496 but i can not get a proper output?

are you thinking that i can do the job with 2N2222 ?is not it too noisy ?is it perfect?

The whole job might be easier to do with frequency modulation. Then you don't need a linear amplifier.

Like I said, it probably is working. You are getting double sideband supressed carrier, NOT AM. If you measure the output frequency, it will be all over the place, depending on modulation. You might be able to get the existing circuit to output AM if you unbalace the carrier, and keep the input signal small enough to prevent over modulation. You need to look at the output with a scope.

Presumably the power will be in the milliwatt range, any transistor will work.

Look, with your 3.9k resistors you saturate the output transistors. 2mA of bias makes 7.8V across , but you bias at 6V, so reduce them to 1k5 and the Re to 220R. Check the square wave level to be not higher than 300mVpp and the analog in only 200mV~. You also have to filter the audio or else you get aliasing, which sounds "inverted" frequency response.

i made a new kind of DSB based 1496, i can get an stable 40kHz carrier with a good DSB at now, but there is another problem, i have the melody voice on the output of 1496! i have it even i cut the

But when you make AM and switch off the carrier then you modulate the DC and have your signal as well on the output. Perfectly OK. You can turn the bias pot all the way to the left side an then you have suppressed carrier DSB. But that is difficult to demodulate in the receiver. Why don't you do FM? You can do that with the 555 alone. Also easy to detect. and no sound on the O/P.