Mc1496

[Roff]

Pardon me for shouting, but YOU DON'T NEED SINGLE SIDEBAND! It would only make your job more difficult. SSB removes the carrier from the signal. You would have to reinsert it in the receiver. How would you do that?
If you do transmit DSB, once DSB has been received, SSB is totally useless in the receiver. Are you under the inpression that one of the sidebands is the final output of your receiver? It is not. You must demodulate the received signal, and to do that, you need the carrier.
The purpose of SSB is to conserve power and bandwidth in a transmitted channel. If you are transmitting ultrasonically, channel bandwidth is unimportant.
Go to Google and read everything you can find about SSB.

 

[epilot]

Pardon me for shouting, but YOU DON'T NEED SINGLE SIDEBAND! It would only make your job more difficult. SSB removes the carrier from the signal. You would have to reinsert it in the receiver. How would you do that?
If you do transmit DSB, once DSB has been received, SSB is totally useless in the receiver. Are you under the inpression that one of the sidebands is the final output of your receiver? It is not. You must demodulate the received signal, and to do that, you need the carrier.
The purpose of SSB is to conserve power and bandwidth in a transmitted channel. If you are transmitting ultrasonically, channel bandwidth is unimportant.
Go to Google and read everything you can find about SSB.

Ok , thanks Ron,

i will go and read more and more about SSB and DSB,

my mean on my last post was asking WHY I DONT NEED FOR SSB?
it seems the problem is that i think if i send the info via DSB i will lose my info because of symmetry in the waves carried by carrier or i must demodelate only one side in the reciever, but since i think if i use from a filter(high or low pass) then i will have the carrier and ONLY ONE SIDE OF THE WAVE then i don't need to use from a filter in the reciever to remove the carrier and ONE OTHER SIDE, but since you and nigel are saying that i don't need for SSB so i am thinking of a mistake in my guess about SSB.

let me correct my question,
if i use from DSB then won't i lose my signal because of symmetry in the waves carried with carrier(please dont shout this is a question that i like to know its answer)

what about amplifying the output of 1496,? do you think i can amplify the out put of 1496 at 40kHz using one or two LM3875 or

 

[Nigel Goodwin]

ok, i have buld the second circuit and it seems it works(i can see amplitude exchanges onmy oscope with modulated signal as input and a 40kHz square carrier wave generated with a 555 ic)
anyway i have a square wave in the output(hope it works instead of a sine wave)

ok i think you want me to removecarrier and one sideband in the reciever, and use from a DSB for the transmitter, is this correct?

Nigel, i think it is possible making a SSB using only one high or low pass filter, if so,why you are saying that "is a VERY different technique"?

For SSB you remove the carrier and modulating frequencies (using a double-balanced mixer - like you have). This leaves the upper and lower sidebands, either of which carries all the information you want. So you remove one of them using a very sharp, narrow-band, filter - it's common to do this at 9MHz, and crystal filters are available for this exact purpose.

At the receive side, because it's no longer AM, you have to reinsert the carrier, and also try and make sure it's EXACTLY the same frequency as the original, or the voice will be the wrong pitch. If you reinsert the carrier the wrong side of the sideband you get a completely unintelligible voice - sort of inside out?, mirror image?, which makes quite an interesting scrambler system.

Bandwidth is poor, quality is poor, but it has the advantage that you don't waste transmitter power sending parts you don't need - which is why it's used for long range radio communication. Only CW (morse code) goes further.

As you already have severe quality limitations, the last thing you want to do is cripple it further, which will also add complications and not really help anything.

As you've said 'AM' all along, I would suggest you stick to proper AM, it's the best 'quality' option of the three low quality modes you've mentioned.

i want to amplify the output of 1496, this means i want to amplify the AM signal, i want to use from an amplifier IC ans since i have some of LM3875(it can Handle more than 50W)i want to use them, what is your idea?
i connect the input of amplifier IC to output of 1496 IC and the ouput of amplifier goes to ultrasonic transmitter,is this a good idea to improve the output of 1496 IC?

You don't really need a lot of 'power', you can feed ultrasonic just from a single transistor if you want - depending on the supply voltage you use. If your supply is only low, using a bridged output stage will give twice the voltage swing.

But for a start I would forget the transducers altogether - connect the output of your modulator to the input of your de-modulator, see how it works, and what quality you get. Obviously the transducers will reduce quality further, but I suspect it won't be great even direct?.

What are you using for a de-modulator anyway?.

 

[audioguru]

The sidebands of an AM radio signal are groups of RF frequencies, a little above and below the carrier frequency.
The symmetry of a modulated AM radio signal has a positive-going and a negative going portion that are identical and they have nothing to do with sidebands or frequencies. The AM signal is demodulated with a diode and a filter capacitor to give the amplitude fluctuations (modulation) of the polarity selected by the diode.

 

[epilot]

What are you using for a de-modulator anyway?.

thanks for all directions.

Nigel i have seen some of circuits using 1496 as demodulator so i'll try this IC for demodulator, but i am working on the transmitter yet.

Unfortunately i could not to get any time to read more about AM yet but i'll do it soon.


i have built the transmitter part, i tuned the square wave oscillator at 40kHz
and made a musical sound by a UM66 IC and sent it into input modulating signal ,then i connected the ultrasonic transducer to the output of 1496 via an amplifier(the scope shows 40Khz on the output line of amplifier)
but there is a problem i think, i can here a weak musical sound via ultrasonic transducer! even i can here the sound via a speaker, i think there is a problem because the output MUST BE A 40KHZ AM and i am wondering why i have the musical voice at output????!!

 

[audioguru]

The modulator IC isn't perfect. A little amount of the modulating signal goes to its output.
Maybe your power supply needs better regulation.
Maybe your amplifier produces even harmonics distortion which attenuates one polarity of the modulated waveform. So the amplifier is performing like an AM detector.

 

[epilot]

The modulator IC isn't perfect. A little amount of the modulating signal goes to its output.
Maybe your power supply needs better regulation.
Maybe your amplifier produces even harmonics distortion which attenuates one polarity of the modulated waveform. So the amplifier is performing like an AM detector.

since i am a beginner in modulation, i am not able to think if this i s a problem or not.


anyway if this is a problem like you are saying, i am sure that the problem is not because of power supply because i am using a commercial regulated power supply(i bought it 100$ so i think it is a good power supply).

i made a test without amplifier, but i had that sound too.

i am using Ron's schematic(the second here) and a 555 square wave generator at 12V.

i think i can put the whole circuit here if it is necessary?

 

[epilot]

Ron:
i used A 10k resistor in series with output of 555 and the modulation input of 1496, is this good?
perhaps there is a problem with this part?
yes i know you said i should use a 12k resistor at 12V but i thought it should work ok with 10k too?

 

[epilot]

i used from a 12k resistor in series with output of generator and input of modulatiing signal input of 1496 but i have the problem yet with alot of noises.

by the way perhaps this helps to find the problem,if i cut the generator output wire, i have the clear voice(loudly)on the output of 1496

 

[audioguru]

i have the problem yet with alot of noises.

The lousy quality of AM produces noises. Noises are amplitude changes. AM is amplitude modulation.
Maybe your circuit isn't shielded and has wires too long and picks-up mains hum and other interference.

if i cut the generator output wire, i have the clear voice(loudly)on the output of 1496

Maybe the audio input level is too high for the MC1496.
Maybe the audio at the output will be cancelled if you use the MC1496 with a balanced output.

 

[epilot]

here are 2 pics of the scope output at 40kHz carrier and a melody as modulated signal

the scope was connected to pin6 of 1496,
you can see that i had 22kHz and 39kHz as output!
but the output seems as an AM.

i don't know i trhink i am becoming confused with the output,
i connected a 22K resistor between the output of melody and the modulating ubput pin but i can here the melody at output???

 

[epilot]

here are carrier oscillator, and modulation that Ron put here

 

[Roff]

OK, here's my suggestions: Set the modulating voltage (the information signal) to 0.5V peak-to-peak. Change Re to 2k. Set the voltage on pin 4 to 3.8V by adjusting the 10k pot. You should get a waveform similar to this one. I used a 1kHz modulating frequency. You can make this whatever you want. Note that by varying the voltage on pin 4, you can change the depth of the modulation.

 

[epilot]

OK, here's my suggestions: Set the modulating voltage (the information signal) to 0.5V peak-to-peak. Change Re to 2k. Set the voltage on pin 4 to 3.8V by adjusting the 10k pot. You should get a waveform similar to this one. I used a 1kHz modulating frequency. You can make this whatever you want. Note that by varying the voltage on pin 4, you can change the depth of the modulation.

Hi Ron,

i did what you said but the result in all tests was gain reducing, and i had the voice at the output of 1496 but weaker and it was because of gain reducing in the chip.

i made a test and saw that i have the amlitude modulation in output of chip (40kHz and modulated signal) this is good but i have that voice too.

don't know perhaps it is normal having that sound at the output with 40 or 50kHz. perhaps i must use from a filter to remove it?

anyway,i have no solution for this chip to remove that sound perhaps it is better i go for AD633 IC,

 

[audioguru]

You hear a weak audio voice signal from the ultrasonic transducer that has 40kHz AM modulation because the transducer has even-harmonics distortion and is acting like an AM demodulator.

The 1496 also has even-harmonics distortion that could be cancelled if you use both outputs as a balanced signal to the amplifier.

 

[Roff]

Your "square wave" carrier oscillator does not produce a 50% duty cycle, which could cause problems. I would change the circuit, or double the frequency and then divide it by two with a toggle flipflop.

 

[epilot]

You hear a weak audio voice signal from the ultrasonic transducer that has 40kHz AM modulation because the transducer has even-harmonics distortion and is acting like an AM demodulator.

The 1496 also has even-harmonics distortion that could be cancelled if you use both outputs as a balanced signal to the amplifier.

i can not understand why and how it acts like a demodulator?!

i have that voice on the output when i cut the carrier pin from the 1496.

sorry but don't know how to use both output?

 

[epilot]

Your "square wave" carrier oscillator does not produce a 50% duty cycle, which could cause problems. I would change the circuit, or double the frequency and then divide it by two with a toggle flipflop.

such as i said before i have that voice even if i cut the carrier oscillator,

can you let me know how can i get that 50% duty cycle for carrier and information pins ?

 

[audioguru]

i can not understand why and how it acts like a demodulator?!

If the transducer moves in one direction a little more than in the other direction then it has even-harmonics distortion and its average movement follows the modulation.
If the input transistors of the MC1496 are not perfect then its output will swing a little more in one polarity than in the other polarity. Then the average will have the modulation.

 

[epilot]

i found this circuit at the data sheet of 1496.

its output is DSB and it works with a single supply(12V)

Ron won't you think i can solve the problem with building this?