Calculation of MER through SNR.

[HIREN DAVE]

Hello,

i use FTA satellite box.(i.e. 950 to 2150 Mhz digital communication). I got SNR in the range of 35dB from STB data. Now, I want to calculate MER from this data. As per my understanding, SNR is a function of MER.

In one reading I got, MER 5.7 db when I am checking with MER meter. But I need exact value of MER from SNR only via STB, how it's possible ?

[Maxwell]

An extremely complex subject and why do you need to calculate if you can measure ?
MER is close to SNR but not a function of it,

MER requires you to know the RMS of the error vector power and the RMS power of the ideal transmission signal - MERdB= 10log10 (Psig/Perr)

The basic SNR used in the receiver is derived using an average measurement and not RMS which can be converted to dB's by
SNRdB= 10log10 (Psig/Pn)

the similarity between the actual equations is very close but there is a big difference between them due to RMS and average figures and other factors not mentioned here.

My head hurts now its been a long time since I had any involvement in this sort of thing :coffee::confused:

[HIREN DAVE]

Hi Maxwell. Thanks for your reply.

I have taken reading from MER meter as a reference. My purpose is to take readings from Set top box.

I am getting following parameters from Set top box. Please tell me these can be useful for finding MER or not?
1. BER
2. SNR (signal quality)
3. AGC (signal intensity)
4. Symbol rate
5. FEC (code rate).

[Maxwell]

Hi Maxwell. Thanks for your reply.

I have taken reading from MER meter as a reference. My purpose is to take readings from Set top box.

I am getting following parameters from Set top box. Please tell me these can be useful for finding MER or not?
1. BER - No, you can have a good MER and a poor BER,
2. SNR (signal quality) No as I already explained its an average and you need RMS of the I,Q plane error vector within the constellation
3. AGC (signal intensity) No simplified this is the tuner lock and control
4. Symbol rate Not relevant for what you want (for any pedants I know it could be to achieve a reference but not here)
5. FEC (code rate). No


Just curious as to why you want to do this ?

One other point is STB measurements are nowhere near accurate enough to give reliable results anyway

If you really want to know the basics of BER/MER have a read of this

[HIREN DAVE]

Thanks a lot.