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Where are the points of a receiver circuit signals waveform that can be seen by an oscilloscope?
- Thread starter BRL6
- Start date
- Tags circuits receiver seen by scope signal waveform
This schematic is small and hard to see.
TP8 at the output will have a signal you can see by an oscilloscope. (output of audio amplifier)
TP6 is a very small audio signal you can see. (input of audio amplifier)
Signals on T1, T2, & T3 are very small and are 455khz IF frequency and Audio together. T3 you probably can see but T1 is so small that a oscilloscope probably can not find it.
Signals at the left most transistor are at RF frequencies, very very small. (micro volts)
TP8 at the output will have a signal you can see by an oscilloscope. (output of audio amplifier)
TP6 is a very small audio signal you can see. (input of audio amplifier)
Signals on T1, T2, & T3 are very small and are 455khz IF frequency and Audio together. T3 you probably can see but T1 is so small that a oscilloscope probably can not find it.
Signals at the left most transistor are at RF frequencies, very very small. (micro volts)
Radio signals that appear at the terminal of your antenna can vary in strength from zero to as high as a few millivolts, depending on how far away the transmitter is and how much power they transmit. Most radio signals that you receive are well below one millivolt. Oscilloscopes are simply not sensitive enough to show these signals. It is not unusual for the most sensitive range on an oscilloscope to be 1 mV per division, and in this range there is often some noise on the trace even with nothing connected to the probe. It is difficult or impossible to see a radio signal of, for example, 50 microvolts, in this noisy trace.
At the antenna there a are millions of radio stations all at the same time. (ok maybe 1000s or 100s)
It will look like noise. If you can see anything.
Hope you can see this picture. The top signal is audio. The middle signal is what a AM radio station transmits. The bottom signal is what a FM radio station transmits.
It will look like noise. If you can see anything.
Hope you can see this picture. The top signal is audio. The middle signal is what a AM radio station transmits. The bottom signal is what a FM radio station transmits.
Thread starter
#8
Very thanks for your useful answers.special tanks to ronsimpson for his great modulations animation.So, in fact,if I want to localize points of a receiver in which we can see a reasonable
signals , which points are there?
Could you please get me those points even at a typical receiver block diagram ?
signals , which points are there?
Could you please get me those points even at a typical receiver block diagram ?
wow, that's a pretty cool kit. i ought to get one for my youngest son. who makes that?
one way to see what's going on in RF and IF circuits is to feed an AM signal from a signal generator. i think most oscopes will be able to see a 100uV signal. so that would allow you to trace the signal all the way through from RF input to audio output. another often used test point would be the local oscillator output
one way to see what's going on in RF and IF circuits is to feed an AM signal from a signal generator. i think most oscopes will be able to see a 100uV signal. so that would allow you to trace the signal all the way through from RF input to audio output. another often used test point would be the local oscillator output
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The problem you might be having is called TRIGGERING.
To get a trace across the screen, the cro needs to look at point on a waveform (called an amplitude) and then start to show the incoming signal.
If you want the TRACE (the waveform on the screen) to be steady, the incoming signal must be exactly the same as the previous cycle or cycles. With most signals in an AM and FM radio circuit, the signal is changing all the time due to voice or music being processed.
The CRO will have a hard time "latching onto" the signal and it generally results in nothing being shown.
You have to firstly read the output of an oscillator that has a completely stable and reliable waveform and get to know how to adjust the TRIGGER LEVEL control.
It has a manual and automatic setting and the difference is normally obtained by pulling the control and thereby clicking the switch that is connected to the shaft.
Once you know how to get a steady trace you can probe higher and higher oscillator frequencies and then go to audio amplifiers that are connected to a signal generator.
You will then the able to read very low amplitude signals.
Once you all this ability you can go to a radio tuned into a TONE and finally you can look at reception signals.
To get a trace across the screen, the cro needs to look at point on a waveform (called an amplitude) and then start to show the incoming signal.
If you want the TRACE (the waveform on the screen) to be steady, the incoming signal must be exactly the same as the previous cycle or cycles. With most signals in an AM and FM radio circuit, the signal is changing all the time due to voice or music being processed.
The CRO will have a hard time "latching onto" the signal and it generally results in nothing being shown.
You have to firstly read the output of an oscillator that has a completely stable and reliable waveform and get to know how to adjust the TRIGGER LEVEL control.
It has a manual and automatic setting and the difference is normally obtained by pulling the control and thereby clicking the switch that is connected to the shaft.
Once you know how to get a steady trace you can probe higher and higher oscillator frequencies and then go to audio amplifiers that are connected to a signal generator.
You will then the able to read very low amplitude signals.
Once you all this ability you can go to a radio tuned into a TONE and finally you can look at reception signals.
