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I do not have too much knowledge background of RF knowledge.

Background:

I am using Arduino board to record and interpret RF analog signals. There is an 10-bit analog-to-digital converter.

Questions:

  1. I saw many people use "threshold voltage" to describe the levels of analog signals (convert to digital). In the case of Arduino's 10-bit ADC, it is level 1-1024.

    So what this "threshold voltage" actually refer to (e.g. strength of analog signal or something else)?

  2. Continue Q1. If the threshold is low than certain value (e.g. 80), it is defined as LOW signal. Similarly, HIGH signal for threshold higher than 100.

    For example, remote control signal (e.g. air-condition) consist of a series of (LOW, HIGH) pairs. This is what I saw from some Arduino projects. Is it a common way to define LOW and HIGH signal?

  3. What means the length of analog signal? Time?

  4. If you convert digital signal back to analog signal, and send them through a transmitter. You need to set certain delay between each (LOW, HIGH) pair. Why there is such delay?

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    \$\begingroup\$ Q1/2: You're confused between a number of things. In the analog world, a defined threshold is meaningless - it's just a choice you make to say something is high or low depending on your application. Threshold in digital refers to the actual voltage a gate will change or be indeterminate. 3. Yes, time. 4. Would need to know more about your setup. \$\endgroup\$ – awjlogan Oct 31 '17 at 7:27
  • \$\begingroup\$ @awjlogan: I understand Q1-3 already. For Q4, this is the application arduinobasics.blogspot.sg/2014/06/…. it said "the signal alternate between LOW and HIGH" is this common for RF remote control? \$\endgroup\$ – TJCLK Oct 31 '17 at 7:35
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    \$\begingroup\$ If you understand Q1 to 3 already why put them in the question so people spend time answering them? \$\endgroup\$ – Solar Mike Oct 31 '17 at 7:42
  • \$\begingroup\$ Q4 then. Yes, the output from a remote is a digital signal (HIGH = ON, LOW = OFF) usually using Manchester encoding. Reason being that the signal to noise is much better than an analog signal. It is usually modulated as well to reduce the effects of ambient light. \$\endgroup\$ – awjlogan Oct 31 '17 at 7:59
  • \$\begingroup\$ @awjlogan: very clear! \$\endgroup\$ – TJCLK Oct 31 '17 at 8:01
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Why is there such a delay, between Hi and Lo, etc? because the various filters will only settle with certain bandwidths. A single RC filter, of time constant 159 microseconds, has bandwidth of 1KHz == 1/(2 * PI * 159uS), Each Tau of settling brings the output voltage 67% closer to the final/steady_state value. I use Signal Wave Explore to demonstrate this

enter image description here

In this example the "system" is just a R+C low pass filter, with bandwidth of 2MHz. The time constant is (1 / 6.28) * 1/2MHz = 0.159 * 500 nanoseconds = 40 nanoseconds.

The time-per-division is 100 nanoseconds; thus in 40% (40nanosecond) of one horizontal division, the output waveform (the lower waveform) moves another 67% closer to final steady-state value.

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