whats mer plz

iwol

hi if a meter has a MER calculation/value has been added function what does it mean plz thanks iwol

kenny1234

Modulation Error rate, its the measurement of modulation distortion very long winded to explain dont know if i can lol, basically the more MER the better.

Plz feel to correct me if i'm wrong but i believe 20db Mer is the threshold 24db or more is ideal

Poor Mer quality can give rise to corruption making the signal unstable.

I went on an understanding Digital signals course and the chap who took it was struggling to put it in laymens terms and thats his job so i wont try lol

Channel Hopper

There is a Modulation Error Ratio rather than rate

_http://zone.ni.com/devzone/cda/tut/p/id/3652

The modulation error ratio (MER) is a measure of the signal-to-noise ratio (SNR) in a digitally modulated signal. Like SNR, MER is usually expressed in decibels (dB). MER over number of symbols, N is defined as:
where
is the I component of the j-th symbol received
is the Q component of the j-th symbol received
is the ideal I component of the j-th symbol received and
is the ideal Q component of the j-th symbol received.

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There is a very fine line between "hobby" and "mental illness"

rolfw

Same here, the training course on the meter covered it, but they were hard pushed to explain exactly what it was, apart from being a combined measurement. It is however a nice measure for dish alignment, as if this measurement is good, then the rest tend to fall into place.

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satelliteman

I always look at MER simply as a digital CNR (C/N) measurement and will vary on what is being measured

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iwol

thanks guys im even more confused now :-)

Channel Hopper

Just wait until you need to know about Eb/No

There is a very fine line between "hobby" and "mental illness"

iwol

im not even asking:-)

patmos

Thank you guys for the definition of MER. I could find its definition on the web.I see that most meter sold will boast that they can measure this unit. I work in a Earth Station and what we checked is the Eb/No,C/N and BER. This term is never used.

black22

QAM MER — Modulation Error Ratio

The modulation error is a calculated quantity indicating the mean or the maximum deviation of the I/Q values from ideal signal states and thus provides a measure of signal quality.

The following diagram shows the vectors used for calculating the modulation error:

The modulation error is specified as rms and as peak value. To calculate the modulation error, all decisions fields are investigated on after the other.

To obtain peak modulation error, the maximum magnitude of the difference vector (error vector) formed by the vector of the ideal and the actual signal status is determined for each decision field. From the maximum value of these results, the peak MER (modulation error ratio) is calculated using the following formula:



To obtain the rms modulation error, the squares of the magnitude of all differential vectors formed by the ideal-status and actual-status vectors are added up, and the number of symbols is counted. Then the rms modulation error is calculated as follows:



The peak and rms modulation error can also be specified on a logarithmic scale. Conversion is done using the following formula:



For quantized I/Q values, the peak value is output in discrete form only since no averaging is performed in the calculation. The rms modulation error can be calculated within the limit values specified in the following table. The limit values are obtained for quantized I/Q values:

Orderof QAM , MERRMS min, MERPK min, MERPK min , MERdB min

4 , 0.5 % 1.563 % 98.44 % 46 dB

16 , 0.5 % 1.398 % 43.32 % 46 dB

32 , 0.7 % 1.976 % 29.33 % 43 dB

64 , 0.5 % 1.364 % 20.46 % 46 dB

128 , 0.7 % 1.952 % 13.66 % 43 dB

256 , 0.5 % 1.356 % 9.471 % 46 dB

Attached herewith the Vector diagram and Formulas to calculate the MER.

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