audioguru said:Similarly, you don't need SSB.
i want to give the IC a 40kHz as a carrier and a 50Hz to 15kHz signal as modulating signal.
audioguru said:The DSB circuit that you attached has a suppressed carrier. So your receiver must re-insert a carrier into the received signal for the modulation to be properly detected. The re-inserted carrier must be exactly the same frequency as the original carrier.
You don't need DSB, the AM that you had is the same except this DSB circuit suppresses the carrier to save transmitting power.
Similarly, you don't need SSB. I made some SSB circuits for voice scrambling and they worked perfectly. I used a switched-capacitor Butterworth lowpass filter IC to filter out the unwanted sideband. With a quartz crystal for the transmit and receive carriers, the unscrambled sound was perfect and the scrambled sound was completely unintelligible.
audioguru said:The modulator IC isn't perfect. A little amount of the modulating signal goes to its output.
.
I'm really not very knowledgeable about ultrasonic transducers. What I meant was, minimizing the amount of bandwidth used is unimportant. See this site for the advantages (and some disadvantages) of SSB over DSB. This article was written with RF transmission in mind. Perhaps some of the advantages would be important enough to try using them with ultrasonic transmission. If your transducer has narrow bandwidth, maybe that would be reason enough to go through the hassle of regenerating the carrier. I don't know.epilot said:Ron:
tonight i reread the whole of this thread, somewhere you said "If you are transmitting ultrasonically, channel bandwidth is unimportant. "
as we know an ultrasonic transducer has a sharp resonant at 40kHz
so it should not be so good for my job, am i wrong?
i know that the carrier is 40kHz but i think i will have something much more than 40kHz at the output of trasducer?!
A transformer is expensive. Look-up Opamp Differential Amplifier in Google. Then both outputs of the MC1496 connect to both inputs on the differential amplifier.epilot said:yes audioguru, i just realized that the problem about having part of unmodulated sound in the output is because of 1496 itself.i found out that i can remove it if i use my chip as a balanced output,
can you let me know how can i use the chip as a balanced output?
i think it is possible using an OP AMP or a transformer with a tap, am i right?
audioguru said:A transformer is expensive. Look-up Opamp Differential Amplifier in Google. Then both outputs of the MC1496 connect to both inputs on the differential amplifier.
epilot said:but i think there is a problem using an OP AMP:
an OP AMP can not be used for ULTRASONIC(please be noticed the output of OP AMP must go to more than 40kHz)
so i think the only way is using a small transformer?
i am not sure what kind of transformer is the best choice?
Nigel Goodwin said:Many opamps are fine at 40KHz, just choose them accordingly.
If going the transformer route you need a specific transformer for the job, which you will most probably have to wind your self?.
A long time back in this thread I suggested ignoring the transducers, and connecting the modulator output via wires to the demodulator - have you ever done this?. There seems little point in worrying about opamps or transformers if the basic circuit doesn't work in the first place?.
epilot said:i have 741, LF411, LF351, LF356 in my hands, what is your idea about using 741 acording to this pic?
Nigel,
i modified the modulator circuitry and could get a good result from its output
and my oscilloscope shows that the circuit works fine except that small sound that passes from the input of the chip to its output,
i have not tried the reciever part yet and i must remove that sound to try the reciever part using another 1496 too.
audioguru said:Like most modern opamps, the LF351 has a power bandwidth to above 100kHz. The old 741 has a max of only 9kHz.
Your opamp differential amplifier has its input pins reversed, is not balanced sincethe values of the 330k and 390k resistors are different and has way too much gain (maybe the modulation level is too low).
I corrected the schematic:
audioguru said:Do you have a 100uF supply bypass capacitor? Maybe the audio is modulating the power supply voltage if the capacitor is missing.
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