2 signals and modulation

[Electronman]

Hello guys,

First, hope it makes sense.
I need to transmit 2 modulating signals just via a carrier signal.
For instance I want to modulate a 100Hz and a 1000Hz as modulating signals by a 400 kHz carrier signal.
Is it possible doing so? If so what kind of modulation is the best choice for this work? I prefer AM but not sure how to send and mix those 2 modulating signal simultaneity?

By the way, can I use DSB AM (with carrier) and use one of sidebands independently to add another signal on it? I want the other sideband to not be affected by doing so to the other sideband.

Thanks in advance

 

[JimB]

I want to modulate a 100Hz and a 1000Hz as modulating signals by a 400 kHz carrier signal.
Is it possible doing so?

Yes, just add the two audio signals together in an audio mixer (an op-amp summing amplifier should do nicely), and use the resulting signal to modulate your carrier.

If so what kind of modulation is the best choice for this work? I prefer AM but not sure how to send and mix those 2 modulating signal simultaneity?

You can use whatever you like, AM, FM, W.H.Y. each mode has its advantages and disadvantages.

By the way, can I use DSB AM (with carrier) and use one of sidebands independently to add another signal on it? I want the other sideband to not be affected by doing so to the other sideband.

Yes it is called independant sideband, it is used commercially but the transmitter and reciever are significantly more complicated.

JimB

 

[Electronman]

Yes, just add the two audio signals together in an audio mixer (an op-amp summing amplifier should do nicely), and use the resulting signal to modulate your carrier.


You can use whatever you like, AM, FM, W.H.Y. each mode has its advantages and disadvantages.


Yes it is called independant sideband, it is used commercially but the transmitter and reciever are significantly more complicated.

JimB

Wow thanks!


Say using AM, if I add those 2 modulating signals then what I will have at the output of the modulator? I am talking about FFT.

what is W.H.Y.?

Again using AM how can I work with that sideband? How can I make it independent?

 

[JimB]

Say using AM, if I add those 2 modulating signals then what I will have at the output of the modulator? I am talking about FFT.

Do you mean what will the spectum of the transmitted signal look like?
Assuming a 400kHz carrier and 100hz and 1khz modulating frequencies, there will be side frequencies at:
399.0khz
399.9khz
400.1khz
401.0khz

what is W.H.Y.?

What Have You = anything you like!

Again using AM how can I work with that sideband? How can I make it independent?

You cannot use a simple AM modulator.
You need an ISB transmitter which generates the upper and lower sidebands independently for a common carrier oscillator.

JimB

 

[flat5]

What are you trying to accomplish?
You might be better of using three modulated signals
or two transmitters or two modes of modulation.

 

[Electronman]

Well, in reality the carrier which I want to use is just 40 KHz not 400 KHz.
I want to use it with an infrared sensor and transmit 2 independent signals at say 100Hz and 1000Hz I want one of those modulating signals to not be affected by the other at the output of the modulator (AM modulator which I prefer to use)

Is there any way to use the carrier itself for one of those signals? I mean using the carrier for the modulator to transmit modulated 100Hz and again using the carrier with 1000Hz to transmit just 41KHz while just using one IR sensor. Is there any way which help and case the carrier to not be changed when used with the modulator and does change with the other signal? (in the second case the carrier must be summed with the 1000Hz. I think I can use it even if it is modulated too, but I am not sure because I have 2 signals).
Please consider that these signals must be send via just one IR sensor.
I think I am vague yet right?!

 

[Electronman]

The final aim is to transmit those 2 independent signals via an IR transmitter sensor and then receive each of them via 2 other IR receivers sensors at say 2 meters and finally hear EACH modulating signal via a headphone. So I will use 2 separate demodulators and 2 headphones to have 2 different modulating signals at the output of each demodulator
Makes sense now?

 

[crutschow]

Using two modulators is more complex then it needs to be. The simple way is to modulate both signals on a single carrier and then differentiate the signals by using two filters on the demodulated output. The demodulated output will consist of the 100Hz and 1000Hz signals. A 100Hz low pass filter will pass the 100Hz signal and suppress the 1000Hz signal. Similarly a 1000Hz high pass filter will pass the 1000Hz signal and suppress the 100Hz signal.

The amount of suppression is determined by the number of filter poles in each filter. A simple, single-pole RC filter will have a suppression of 20dB/decade (a factor of 10) which is what you have here since the signals are a decade apart.

If you need more suppression you would use a higher order filter. Each increase in filter order improves the suppression by a factor of 10 (20db). An op amp two or three pole active filter would work well. A good design tool for designing active filters is from TI: Active Filter Design Application - FILTERPRO - TI Software Folder.

EDIT: The above won't work, of course, if the two modulating signals are near each other in frequency or overlap in frequency, such as two audio signals.

 

[JimB]

Here we go again!
Only half the story, and the bit we do get has errors in it!

Forget everything I said about ISB, I dont think that amplitude modulation is at all relevant to Infra Red systems.

JimB

 

[kchriste]

What are you trying to build? IR remote stereo headphones?

 

[Electronman]

Using two modulators is more complex then it needs to be. The simple way is to modulate both signals on a single carrier and then differentiate the signals by using two filters on the demodulated output. The demodulated output will consist of the 100Hz and 1000Hz signals. A 100Hz low pass filter will pass the 100Hz signal and suppress the 1000Hz signal. Similarly a 1000Hz high pass filter will pass the 1000Hz signal and suppress the 100Hz signal.

The amount of suppression is determined by the number of filter poles in each filter. A simple, single-pole RC filter will have a suppression of 20dB/decade (a factor of 10) which is what you have here since the signals are a decade apart.

If you need more suppression you would use a higher order filter. Each increase in filter order improves the suppression by a factor of 10 (20db). An op amp two or three pole active filter would work well. A good design tool for designing active filters is from TI: Active Filter Design Application - FILTERPRO - TI Software Folder.

EDIT: The above won't work, of course, if the two modulating signals are near each other in frequency or overlap in frequency, such as two audio signals.

How can I modulate both signals on a single carrier?

I want to have a 'carrier + a side band' and another independent signal (proportional to the second modulating signal) at the output of the modulator (I.e on that IR transmitter sensor).

Anyway I do not like the filtering solution!

 

[Electronman]

Here we go again!
Only half the story, and the bit we do get has errors in it!

Forget everything I said about ISB, I dont think that amplitude modulation is at all relevant to Infra Red systems.

JimB

But maybe ISB is the best solution to go for?

 

[Electronman]

What are you trying to build? IR remote stereo headphones?

I told what I want to make!

I want to transmit 2 signals via just an IR transmitter sensor and then receive each one independently at 2 receivers. I do like a modulator to do the modulation for both transmitted signals.

 

[Nigel Goodwin]

I told what I want to make!

I want to transmit 2 signals via just an IR transmitter sensor and then receive each one independently at 2 receivers. I do like a modulator to do the modulation for both transmitted signals.

Still makes no sense to me either - you're telling us what you think you need to do, not what you're wanting to do.

What EXACTLY are you trying to achieve?.

 

[kchriste]

Describe these two signals better then. I assume they are analog. You still haven't told us what bandwidth you want per channel:
Chan A: 0 - xxKhz?
Chan B: 0 - xxKhz?
etc.
Fill in the xx's above and then we'll talk about dynamic range.
Vague requirements will get you vague answers.

 

[Electronman]

Well I want to transmit the human speech by the IR Transmitter sensor. suppose 2 guys who are talking in front of 2 microphones while one IR sensor transmits those 2 sounds independently.
It is a final project of a friend who wants me to help him.

I thought and specially like to use modulation to do the project.

Yes they are analogue signals kchriste. And the bandwidth is between 300Hz to nearly 3000Hz

 

[crutschow]

If you told us right off that you wanted to transmit human speech it would have saved us a lot of wheel spinning. Why the secrecy?

 

[ronp849]

Are you saying you want a 100Hz or 1000Hz signal to convey human speech with a bandwidth of 2.7KHz???

 

[ronp849]

You could try sampling the human speech at an appropriate rate and TDM the 2 channels onto the carrier.

 

[Electronman]

Well I wrote my main willing when I started this thread but unfortunately when I read it before posting it I noticed that you can not understand me (I am not an english speaker and when I wrote it I was so tired so I changed the message with that example) so I changed the writing with a simple example so that I tell you what I need to do.

Are you thinking that I told you another thing at the first?? I told you that I want to receive the signal by 2 headphones so they can be speech too!

"ronp849"
I want to trannsmitt human speech with IR and if I notice that It is not possible then I will try just those pure 100Hz and 1000Hz signals (no bandwidth is needed so)