Talk:Modulation error ratio

SNR?
In what way is MER different from post-receiver-filter 1/SNR? According to this article, they are identical; therefore this article should really just be a redirect to Signal-to-noise ratio. Oli Filth 23:05, 3 January 2007 (UTC)


 * The external link you've given actually defines "MER" as (received signal)/(error), i.e. the reciprocal of what this article current says. Oli Filth 00:18, 4 January 2007 (UTC)


 * You're right, MER in decibels is usually a positive number. And as you probably already realized, MER includes all ipmerfections, only including noise. Especially in older analog implementations there are many non-stochastic nonidealities as IQ phase and amplitude error, carrier suppression, or amplitude compression at the corners (ETSI ETR 290). Thanks for reviewing, I'll fix. Alinja 07:57, 4 January 2007 (UTC)

The difference between MER and 1/SNR is that MER includes static, systematic errors in the location of the constellation points as well as those related to noise. MER is, if you like, an overall figure of merit for the system. —Preceding unsigned comment added by 87.85.137.100 (talk) 07:52, 8 April 2011 (UTC)

Sign of dB and Percentage
There seems to be actually 2 versions of the MER definition. Early drafts seem to define it as a negative number (in a similar way that EVM is defined and now correctly fixed in the EVM article), but it was changed to signal/error at some time before ETR 290 Errata 1 (May 1997). But when a percentage representation is used, it is in the less than 100% format, so I'll change that one more time. Alinja 19:52, 9 January 2007 (UTC)


 * By the current definition, we now have that MER(%) is inversely proportional to MER. This is clearly not sensible; it's either (signal/noise) or (noise/signal).  We need to choose one or the other.  However, the fact that "modulation error ratio" brings up only 9 results on Google Groups implies that is MER is not a commonly-used term, and therefore implies that there's probably no "standard" definition; therefore we're at liberty to choose our own.  I would vote for (signal/noise).  Oli Filth 01:02, 10 January 2007 (UTC)


 * 9 results? I get 2250 (MER) vs. 2300 (EVM).


 * gives me 9 results. The fact that no-one talks about it implies that its usage is really not all that common.  However, I could well be wrong - I don't work in the cable tv industry.  I've never come across the term before; my field is wireless DSP in general.


 * Similar search for error vector magnitude gives 19 results.


 * MER is a commonly used term, at least in the cable tv industry. I agree that this is a somewhat strange situation, but we can't change it merely by choosing. ETR 290 clearly has a definition for MER in dB, and the current state of the article is correct (signal/error). ETR 290 doesn't specify MER as a percentage, but in reality it is shown by measurement devices. Examples of such are Rohde-Schwartz EFA test receiver and Agilent PSA spectrum analyzer (although calling it EVM but the definition can be chosen to be like MER).


 * I don't understand. Are you saying that they call the measurement EVM?  In which case, isn't that different to calling it MER?


 * There's a separate setting that lets you choose the average rms power as the reference, but it doesn't change the text 'EVM' in the display. I probably doesnt change the sign of the dB number either, but this is really not important for understanding. It's a kind of shame that ETR 290 defines it in a inconsistent way


 * The numbers shown are always < 100% (as would be in error/signal) as in EVM. The most rational and consistent definition would be to always use error/signal, but that's not the case. Maybe a note could be added to the article about this strange definition, but unless there are sources that show otherwise, I don't see a reason to change the definition itself. Alinja 18:10, 10 January 2007 (UTC)


 * Do you have a link/reference to some documentation/user manual which defines MER as (error/signal)? Oli Filth 20:00, 10 January 2007 (UTC)


 * MER is error/signal when displayed as a percentage (it would not even make sense to display it as thousands of percent). It is specified in the manuals but none of them seem to be freely available. You can see screens of EFA though. Maybe we need a third opinion on this? Alinja 06:58, 11 January 2007 (UTC)


 * The screenshots do indeed confirm what you are saying. This is a strange situation; as one value of MER goes up, the other goes down!  Oli Filth 08:24, 11 January 2007 (UTC)

Special use by catv industry?
Being a wireless digital guy, I too had never heard of MER until someone mentioned it to me in a recent email. If it's a specialized term used only in the CATV world, shouldn't there be a note to this effect in the article? Also, if there's this much confusion over whether it's error/signal or signal/error, that too should be explained in the article and a [sic] placed next to the formulae. Karn (talk) 01:10, 25 April 2009 (UTC)

RMS power...
... as well defined root mean square values is passible of calculation, but do not have any phisical meaning and, so, no practice use. There is no such a thing called "RMS power", as expressed by 'square root of average value of squared function' with phisical meaning and useful pratice. Although RMS value for any given power function may be evalueted — and this is correct! — such an encountered result shows no meaning and useful pratice. IF ANYONE CAN PROOF I AM WRONG, PLEASE, I AM WAITING FOR. THANKS FOR ALL. Aainitio (talk) 19:14, 23 December 2015 (UTC)

You are correct - "RMS power" is a non sequitur in this case. RMS usually refers to a voltage (or electric current or e-field strength, etc.) and is the square root of the mean square voltage, so in this sense, RMS voltage is related to the average power because average power is proportional to average squared voltage. RMS power, on the other hand, wrongly suggests squaring the power, averaging, and then taking the square root. Instead of "RMS power", this should be written as "average power" throughout the article. There is no need to bring RMS into this discussion unless MER is defined in terms of voltage levels instead of power. 96.45.216.240 (talk) 21:02, 25 April 2016 (UTC)