QBox S2 Signal Level Reporting

[sfdataguy]

Just received QBox S2 and it works well - I found that it came with a support file for TSReader which is very useful.

The only problem I have found is with the signal level reporting, when locked both Signal Level and Quality report 98% at all times in both TBS Veiw or TBS IP Data apps.

I am running Windows 7 Pro, 64 Bit with S2QBOX.SYS version 2.0.4.0 dated 1/5/2011

[cody]

maybe, your signal is just very strong and over 16 dB. also, i will check the drivers, because it could be that we re-introduced in the latest version an old bug in signal quality measurement, but if not then 98% are reported only when the signal is over 16 dB, if the signal is less than 16 dB let's say for example 10 dB then (10/16) * 100 = 62-63% in percent is reported.

[sfdataguy]

Thanks for the quick response

I'd agree that's likely if the Eb/No was 16dB or higher. However the Eb/No on both signals I tested with is around 11dB - I'll see if we can run some lab tests to see what's reported with a lower Eb/No level.

[sfdataguy]

OK - It does vary but the point where the readings max out is lower than 16 - not sure if you were referring to C/N or Eb/No in your note but either way in my tests the point where it 'rails out' is an Eb/No of 11.5dB

I testedin a lab with a 30Msps QPSK R=5/6 carrier and measured the reported Quality as the C/N into the receiver was adjusted, then the Eb/No was calculated from the C/N data. Don't know how this varies at other combinations of symbol rate, FEC, DVB Type and modulation.

The results are in the table below.

Code: Select All Code

Eb/No   Quality
   
1.34   0
2.34   45
3.41   50
4.54   56
5.27   62
6.21   68
7.34   75
8.45   81
9.53   88
10.60   93
11.54   98
12.58   98
13.61   98
14.54   98
15.66   98
16.37   98

Didn't test the Signal Level reporting yet

[cody]

ok, i checked the driver - it's currently set to 14 dB C/N for 98% in version 2.0.0.4

[jw300]

I have found the receiver will not lock to any signal with quality below 30%. I don't recall seeing any signal over 94%.

Signal level is always 98% while the LNB is connected, even pointing at empty space. My other receiver reports 99%.

[sfdataguy]

Cody - thanks for the confirmation

14dB C/N corresponds to an Eb/No of 11.96dB with DVB-S QPSK R=5/6 - on the downlinks I was initially trying the box on the Eb/No is 11.8dB and 12.6dB which explains why I was seeing 98% on both.

You might want to think about setting that scale a little higher such that 14 or 15dB Eb/No corresponds to 100% (C/N of 16 or 17dB respectively)

[cody]

yes, actually, it's really very stupid that Microsoft made Windows BDA to require the signal quality to be reported in percents, because there is no way to convert dB to percents and provide accurate information that can satisfy all customers - for example initially for 100% signal quality it was set 16 dB C/N in the driver as you're suggesting, but then more not-technically-skilled customers start complaining that the signal quality is too low and that's why we decreased it to 14 dB C/N for 100%.

[sfdataguy]

Ha - I actually thought that might be the reason it's set where it is ! (kind of like the number of bars on an iPhone..)

As long as I know what the rough calibration is then that's the most important thing.

I appreciate the technical detail and the openness of your responses.

[cody]

BTW, if you look to get some signal statistics - our Linux drivers provide comprehensive details about that, because Linux API support it - for example the latest USB box model:

http://www.tbsdtv.com/english/product/qbox3.html

has such driver and it can report, dBm, dB in C/N, actually/effectively tuned frequency (i.e. frequency offset), actual/effective symbol rate (i.e. symbol rate offset), detected FEC and modulation of the signal, etc. in short - almost all details you can think of about the locked signal.