Hi
I'm trying to make measurement of MER value of a DVB-C source (setup: QAM16, symbol rate 6.9 Msymbol/s, center frequncy 850MHz, bw 8MHz ). I have measured the MER value with an other instrument (R&S EFA) which measure 42dB, but with my EXA with the VXA sw i'm only able to measure 29.4dB.
My questions are:
Is a MER value of 29.4dB the limit of the instrument?
Is it a mean value or a minimum value the instrument outputs?
I'm trying to make measurement of MER value of a DVB-C source (setup: QAM16, symbol rate 6.9 Msymbol/s, center frequncy 850MHz, bw 8MHz ). I have measured the MER value with an other instrument (R&S EFA) which measure 42dB, but with my EXA with the VXA sw i'm only able to measure 29.4dB.
My questions are:
Is a MER value of 29.4dB the limit of the instrument?
Is it a mean value or a minimum value the instrument outputs?
The EXA MER value is not limited to 29.4 dB. For the QAM signal you are measuring, it will be > 40 dB. See attachment from the EXA specifications guide.
There is a minor difference between SNR and MER:
Signal to Noise Ratio (Modulation Error Ratio) is the signal-to-noise ratio, where signal is the average symbol power of the transmitted waveform and noise power includes any term that causes the symbol to deviate from its ideal state position, such as additive noise, distortion, and ISI (inter-symbol-interference). The following formula shows how SNR is computed:
SNR and MER are equivalent as long as noise is the only source of error (or at least the dominant one). There are impairments that would affect an MER calculation without affecting a true SNR measurement. But usually people assume MER equals SNR as long as no obvious impairments show up during demodulation (IQ imbalance, carrier feed through, compression etc).
Having said that, without knowing the actual setup for EFA and EXA, I will be unable to explain why the difference. I will need to know the details of how the EXA was setup and also the input power level of the input signal. The fastest way for you to resolve you queries for this question will be to call the Agilent contact Center number for your country with the details I have asked you above. You can find the number at http://www.agilent.com by selecting the right country.
I hope this was helpful -