I have conducted experimental in my lab that required me to up-convert (modulated) my signal being transmitted via transmitter and down-convert (demodulated) after my message received at receiver, I notice my received signal is suffered from serious clipping effect.
Below are some troubleshooting I have done to trace cause of the effect, but everything seem in perfect order.
1. I have confirm that my Digital to Analog Converter (DAC) and Analog to Digital Converter (ADC) working fine, where I able to get back signal that being transmitted. I don't think clipping issues cause from both of my DAC and ADC
2. But, with complete mixer configuration my received signal seriously suffer from clipping effect.
3. I have carefully feed mixer (both up-convert and down-convert) with appropriate power (LO) and take necessary consideration of power losses but none of them reduce the clipping effect.
4. Even after swap with different mixer, antenna and signal generator the clipping effect remain the same.
5. Message signal is recorded without any amplification or auto gain effect.
Have anyone have any idea on how to reduce clipping effect or even better ripped off those clipping effect. Kindly please advise me.
Thanks in advance
Dear Nur,
In order to locate the main cause of clipping one has to see the wave forms of the signals at the inputs and outputs of the modulator and demodulator. especially the modualted signal.
However, i would suspect that the amplitude of the modulating signal at the input of the modulator is too large and you have to reduce it for linear operation pf the modulator.
The same also for the demodulator the amplitude of the modulated signal may be too large and out of the linear range of the demodulator.
The remedy of this is to divide the output signal from the D/A converter by a potential divider. The same can be done with any signal to reduce it.
Best wishes
Dear Nur,
In order to locate the main cause of clipping one has to see the wave forms of the signals at the inputs and outputs of the modulator and demodulator. especially the modualted signal.
However, i would suspect that the amplitude of the modulating signal at the input of the modulator is too large and you have to reduce it for linear operation pf the modulator.
The same also for the demodulator the amplitude of the modulated signal may be too large and out of the linear range of the demodulator.
The remedy of this is to divide the output signal from the D/A converter by a potential divider. The same can be done with any signal to reduce it.
Best wishes
Check the following.
1. Whether there is any DC coupling. In any case, couple the inputs and output by suitable capacitors.
2. If the clippings are symmetric in positive and negative cycles, reduce the inputs to the output amplifier by potential divider. The supply voltage of the final amplifier may also be increased to solve the clipping.
Seems like the modulated signal amplitude went across the linear operational region of some parts of the system. I would suggest to check back-to-back configurations with all the DC coupling components you used in your system without the up/down-conversion part and see the received waveforms as a start. Then if possible do an amplitude sweep of your modulated signal. Also check the transmitted and received signal from the frequency domain may help, since higher order harmonics may appear during modulation/demodulation.
All the above are things you need to consider. Clipping is caused by amplitude over-saturation in one part of the signal chain. If you change your equipment by stepping up the sample rate for the A/D and D/A to say 1M (not as expensive as you might think) you can streamline the signal chain and have better control over signal collection and play back. As a troubleshooting technique step through you apparatus inputs and outputs to determine the offending stage.
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