# Distinguish two signals of same frequency

Discussion in 'General Electronics Chat' started by Teslafan, Nov 25, 2014.

1. ### Teslafan Thread Starter New Member

Mar 8, 2011
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Hi, I was wondering if there is any possible way to have two sources in series in a circuit of the same frequency but on different voltage and could take distinguish the results of just one of them.
Thanks

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Can you modulate the sources?
Are the signals analogue or digital?
What frequency?

3. ### Teslafan Thread Starter New Member

Mar 8, 2011
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My problem is that i have a voltage source 240 V, 50 Hz and i want to insert a voltage source in series, around 24 V and also 50 Hz. Then i want to have the results from only the low voltage source without the ones of high voltage. The low voltage signal can be of any format i want (square wave, modulated etc).

4. ### Robin Mitchell Well-Known Member

Oct 25, 2009
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You could subtract the two voltages via an op amp.

5. ### alfacliff Well-Known Member

Dec 13, 2013
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no that probably woud not work. unless poth power sources had the same power levels. that would be the same as modulating the 240 volt source with the 24 volt source then.

6. ### djsfantasi AAC Fanatic!

Apr 11, 2010
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Is the high voltage source always present and the low voltage source modulated?

There are four possibilities for the sum of the sources. 0, L, H & H+L. Each case identifies which signal(s) is(are) present.

7. ### Teslafan Thread Starter New Member

Mar 8, 2011
25
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Consider the high voltage to be the voltage source feeding a house and cannot be disconnected. The low voltage is a custom signal of my own that can be of any format and modulation i want. I am asking for a way to measure with my oscilloscope only the 24 V signal without turning the basic supply off..

8. ### GopherT AAC Fanatic!

Nov 23, 2012
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If the signals are in phase, they will add (if there is no significant load on the 24v source because I assume you are operating within some device with a lower-impedence 24v source vs the mains 240 supply.

If there is a slight load, the 24V signal will drop somewhat. If there is a significant load, the 24v signal will drop off considerably.

If you look up X-10 protocol, you will see that mains AC can be a carrier wave for a pulsed communication (5v I think). It is intended for inside a single house - appliance control, for example.

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9. ### djsfantasi AAC Fanatic!

Apr 11, 2010
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You say both sources are 50Hz and safely in series, correct? Are the frequencies synchronized with each other? If so, extracting the signal would be as simple as subtracting the 240vac.

Since you are dealing with high voltages, your circuit needs protection against HV surges and feedback into your LV components.

10. ### kubeek AAC Fanatic!

Sep 20, 2005
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Why does your signal need to be 50Hz? How do you plan to put that signal in series with the mains supply? Can you show a diagram of what you have in mind?

11. ### Teslafan Thread Starter New Member

Mar 8, 2011
25
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X - 10 protocol is a nice thought but it uses an RF signal and that is not going to work in my case. I need the signal to have a frequency of 50 Hz so i can get the total circuit impedance correctly. The series connection part is a hypothesis, i am still trying to figure it out.

12. ### kubeek AAC Fanatic!

Sep 20, 2005
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Huh? Why? What circuit exactly are you talking about?
Twelve posts and still no one has a clue on what you are actually trying to accomplish.

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13. ### GopherT AAC Fanatic!

Nov 23, 2012
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The X10 comment was meant to give you an idea of how to implement your signal on a mains signal - what the physical circuit can look like.

Also note that, if you are operating 50 Hz in phase or 180 degrees out of phase, you may be hindered with false signals as line voltage will fluctuate through the day - even by the minute or second as a motor at a local company turns on/off.

The question is hard to answer because you have placed extraordinary design limitations on your own project. There are do many better ways of doing this (what ever it is you are trying to do).

14. ### alfacliff Well-Known Member

Dec 13, 2013
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how will the 24 volt affect the 240 volt line when a cofee pot isw turned on? unless it has the same current possable to the 240 volt, it will just fade away. how much difference in a 240 volt ac 50 hz line with a few amps when you couple a 24 volt ac, 50 hz in phase or out, at a few ma. into it? not very much at all, I'll bet. it would be better to use a carrier frequency.

15. ### GopherT AAC Fanatic!

Nov 23, 2012
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Exactly what I was trying to say in post #8. I am just concerned that the OP is trying to pump a low impedence signal into the mains line and possibly cause distortion for the rest of his appliances and even his neighbor's mains.

This project seems like a boondoggle to me.

16. ### Teslafan Thread Starter New Member

Mar 8, 2011
25
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I am not trying to sabotage my circuit or my neighbor's one! I am trying to think of an idea of a test signal that can be applied in a house mains and by analyzing that signal to receive information about total impedance, load model etc. I just want to find a way to apply the signal while the mains are still on so it can be more useful in real events. It is a project i am trying to do. Hope everything is clear now.

17. ### alfacliff Well-Known Member

Dec 13, 2013
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like putting a double a battery in series with your car battery, you wil measure 1.5 volts more, till you hit the starter. for power on measurements, use a clamp on ampmeter. there are also clampons for osciliscopes to analyze the load.

18. ### kubeek AAC Fanatic!

Sep 20, 2005
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So, if I get it right, you want to analyze what loads are connected to your home, i.e. if they are capacitive or inductive.
Then why not simply use the mains power as your test signal, measure current at the input panel as well, and then simply do the calculations to measure the phase angle etc.?
I dont see any possible way in which you could add your test signal at 50Hz to your home grid without destroying something in the process.

19. ### Teslafan Thread Starter New Member

Mar 8, 2011
25
0
That was my question too when i first read the project but this was the challenging part and i had to give it a try.. Thanks anw

20. ### BR-549 Well-Known Member

Sep 22, 2013
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What property of a live house mains circuit, can not be determined by measuring the voltage and current?