dBmV?

Ricky91t

Hello all,
I was just trying to help out a user on the irish isp forum by comparing our "RF parameter stats",The user is closer to the mast so therefore should have a better signal but can you just tell me if that's right?

Him: Signal to Noise Ratio: 25 dB
Me: Signal to Noise Ratio: 26 dB

Him:Upstream
/Power: 30 dBmV

Me: Upstream
/Power: 34 dBmV

Him Downstream
/Power: -4 dBmV

Me: Downstream
/Power: -5 dBmV

Can anyone tell me if his/mine are better.

watty

1dB in SNR is very little difference and not significant.
your 26dB is better.
SNR can vary by 1dB to 4dB for different Radio Sets depending on design & technology apart from any real received Noise & Signal. Hence Satellite LNBs have a quoted NF (which is usually meaningless on it's own). Equipment noise is simply added to link noise.


Upstream.
Lower power means better as the base adjusts your local TX to give a desired SNR at base RX.
your Upstream is 34dBmV, i.e. 4dB higher, thus 4dB more loss on link.

Downstream
A larger -ve is LESS signal, thus -4dBmV is better than -5dBmV, but 1dB is very little. From downstream you would expect your SNR to be 1dB worse than his. He is 1dB worse, the 2dB discrepency is within the test limits of some makes/models/technologies of Wireless WAN gear. Also there are other sources of noise and measurement inaccuracies.

Conclusion
His Rx is 1dB better, his TX is 4dB better, his SNR is 1dB worse. Not significant unless the QAM is very high or FEC low etc and you also are on edge of working SNR.

Without more information I don't know what the minimum SNR is. Once you have enough SNR (which depends on QAM, FEC, bandwidth/symbol rate) then more makes no difference.

my signal (likely a different system so irrelevant):

RF Parameters
Downstream
Frequency		Power	0 dBmV
Signal to Noise Ratio	29 dB	Modulation	QAM64
Upstream
Frequency		Power	46 dBmV
Upstream Data Rate	2560 Ksym/sec	Modulation	QPSK

Most systems use bigger steps than 1dB for changing upstream power and have hysteresis, so the upstream power is not interesting or relevant unless it has reached your local TX maximum (very bad).

Ricky91t

watty wrote: »

1dB in SNR is very little difference and not significant.
your 26dB is better.
SNR can vary by 1dB to 4dB for different Radio Sets depending on design & technology apart from any real received Noise & Signal. Hence Satellite LNBs have a quoted NF (which is usually meaningless on it's own). Equipment noise is simply added to link noise.


Upstream.
Lower power means better as the base adjusts your local TX to give a desired SNR at base RX.
your Upstream is 34dBmV, i.e. 4dB higher, thus 4dB more loss on link.

Downstream
A larger -ve is LESS signal, thus -4dBmV is better than -5dBmV, but 1dB is very little. From downstream you would expect your SNR to be 1dB worse than his. He is 1dB worse, the 2dB discrepency is within the test limits of some makes/models/technologies of Wireless WAN gear. Also there are other sources of noise and measurement inaccuracies.

Conclusion
His Rx is 1dB better, his TX is 4dB better, his SNR is 1dB worse. Not significant unless the QAM is very high or FEC low etc and you also are on edge of working SNR.

Without more information I don't know what the minimum SNR is. Once you have enough SNR (which depends on QAM, FEC, bandwidth/symbol rate) then more makes no difference.

my signal (likely a different system so irrelevant):

RF Parameters
Downstream
Frequency		Power	0 dBmV
Signal to Noise Ratio	29 dB	Modulation	QAM64
Upstream
Frequency		Power	46 dBmV
Upstream Data Rate	2560 Ksym/sec	Modulation	QPSK

Most systems use bigger steps than 1dB for changing upstream power and have hysteresis, so the upstream power is not interesting or relevant unless it has reached your local TX maximum (very bad).

Cheers for the reply watty!



My signal,Looks like the same status menu anyway:

RF Parameters
Downstream
 	Power: 	 	-5 dBmV 	 
 	Signal to Noise Ratio:  	26 dB 	 
 	Modulation:	QAM64	 
Upstream
 	Power:		34 dBmV 	 
  	Channel Type: 	DOCSIS 1.x (TDMA)	 
  	Symbol Rate: 	2560 kSym/sec	 
  	Modulation: 	QPSK

I'm guessing those stats are from a Permanet modem? If so I see they switched to 64QAM, they were always on 16QAM before, at least from Knockanore anyway.

Ricky91t

Karsini wrote: »

I'm guessing those stats are from a Permanet modem? If so I see they switched to 64QAM, they were always on 16QAM before, at least from Knockanore anyway.

Funnily enough,It's now been moved back to 16QAM,Something to do with the new packages i guess.