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Hello.
The idea would be to use Si5351 to generate the frequency to the antenna. After measuring with an impedance bridge.
But the IC has a very low power output ... I'm afraid it's not enough.
What do you think?
Re: Using Si5351 to calibrate antenna (impedance measurement)
Sorry, my mistake :oops:.
It is actually a si5351.
I've been watching too many references ...
Hello.
I'm with some doubts.
I want to build a device to measure the impedance of an antenna (arround 14MHz).
The antenna should have an impedance of 50R.
I can connect the output of the SI5153 to an antenna?
If the antenna has an impedânica of 50R (resistive), 5.6mA is enough?
The impedance...
I've done the measurements.
See the following images.
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I'll do more tests. I noticed that the little TPA6205A puts some noise in the audio output.
I'll test without using this IC.
- - - Updated - - -
Input audio...
Hello.
I recorded the sound (direct to the microphone input) after the low pass filter PWM.
The frequency analysis chart was quite different.
But still some peaks appear without explanation ...
Test with 1kHz input.
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OK, this is true and I understand the Nyquist theorem.
That is why my sampling frequency is 40KHz and I want to do experiments with signal only up to 5KHz. So I guarantee minimum quantity sampling.
But this chart is generated by audacity with recorded sound from the microphone.
The microphone...
Hello.
I dont understand...
I recorded using a microphone ... maybe I should put the sign on the microphone input and record again?
Thus there may be no signal above fs / 2 ....
Hello.
Each time the pulse 1 changes its state, the program began a new cycle.
The PWM pulse is 2.
So:
sampling frequency
1 / (26.5417uS) = 37.677KHz
frequency PWM
1 / (5.3333uS) = 187.500KHz
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Ok, I am still reading about this.
But for now if I change my sampling to 12bit, the noise power will be reduced by 1/256 (-24dB)?
It is what you suggest me to do?
but I still do not find explanation to the peaks of the frequencies of the last post....
Hello.
I apologize for the delay.
I played a frequency of 1 kHz (http://www.youtube.com/watch?v=PyD9cMarVJk) for 30 seconds, then I did the spectral analysis.
On the left of the peak 1kHz, I have 2 peaks at 120HZ and 410Hz, but I have no idea what it might be.
The frequency is 40KHz loop...
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