MC1496

[[email protected]]

hello,

recently i am working on AM modulation using MC1496.
i want to modulate a melody with a 40kHz carrier,
i used 555 IC as carrier oscillator(the output is a square wave).
it seems there is a problem, because my oscilloscope shows a range
between 29 to 39kHz at the output of MC1496 while the carrier is
stabled at 40kHz?!

i amplified the output of 1496 and connected it to a trasducer,
i can here the noisy melody at the output of amplifier??!
i think there is a problem because i am using ultrasonic as carrier and
expect to have a 40kHz modulated signal but hear the melody at the
output????

can someone direct me what the problem is really?

thanks for any help.

 

[Leon]

hello,

recently i am working on AM modulation using MC1496.
i want to modulate a melody with a 40kHz carrier,
i used 555 IC as carrier oscillator(the output is a square wave).
it seems there is a problem, because my oscilloscope shows a range
between 29 to 39kHz at the output of MC1496 while the carrier is
stabled at 40kHz?!

i amplified the output of 1496 and connected it to a trasducer,
i can here the noisy melody at the output of amplifier??!
i think there is a problem because i am using ultrasonic as carrier and
expect to have a 40kHz modulated signal but hear the melody at the
output????

can someone direct me what the problem is really?

thanks for any help.

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


Leon

 

[[email protected]]

here are the pics of MC1496 and carrier oscillator circuitry
http://www.ebazargani.com/host2/13715LM1496 amplitude modulator1.PNG

http://www.ebazargani.com/host2/241473.JPG

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??!

 

[Rene Tschaggelar]

hello,

recently i am working on AM modulation using MC1496.
i want to modulate a melody with a 40kHz carrier,
i used 555 IC as carrier oscillator(the output is a square wave).
it seems there is a problem, because my oscilloscope shows a range
between 29 to 39kHz at the output of MC1496 while the carrier is
stabled at 40kHz?!

i amplified the output of 1496 and connected it to a trasducer,
i can here the noisy melody at the output of amplifier??!
i think there is a problem because i am using ultrasonic as carrier and
expect to have a 40kHz modulated signal but hear the melody at the
output????

can someone direct me what the problem is really?

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

Rene

 

[[email protected]]

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!

 

[Leon]

here are the pics of MC1496 and carrier oscillator circuitry
http://www.ebazargani.com/host2/13715LM1496 amplitude modulator1.PNG

http://www.ebazargani.com/host2/241473.JPG

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??!

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

 

[Rene Tschaggelar]

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

Don't know yet.

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

The signals on the scope are simpler to interprete.

Rene

 

[Tam/WB2TT]

hello,

recently i am working on AM modulation using MC1496.
i want to modulate a melody with a 40kHz carrier,
i used 555 IC as carrier oscillator(the output is a square wave).
it seems there is a problem, because my oscilloscope shows a range
between 29 to 39kHz at the output of MC1496 while the carrier is
stabled at 40kHz?!

i amplified the output of 1496 and connected it to a trasducer,
i can here the noisy melody at the output of amplifier??!
i think there is a problem because i am using ultrasonic as carrier and
expect to have a 40kHz modulated signal but hear the melody at the
output????

can someone direct me what the problem is really?

thanks for any help.

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

 

[[email protected]]

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?

 

[Tam/WB2TT]

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.

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

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

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.

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

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

 

[Ban]

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?

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.

 

[[email protected]]

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
60kHz oscillator from 1496, so there is an interferences in the output
of 1496?!

 

[Ban]

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 60kHz oscillator from 1496, so there is an interferences in the
output of 1496?!

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.