View Full Version : SNR in info bar in dB
Is it possible, or could it be added.
In other images, for example Nemesis 2.2.1 for the Dreambox, the SNR is displayed in dB which is much more useful than the percentage figure in VIX. dB is what is used in signal meters and most other decent receivers so it would be much easier to cross reference with other people. Also once the percentage reaches 99% it is impossible to decide if there is any improvement, whereas with the dB figure if there is an improvement the number continues increasing.
Is the ability to display SNR in dB governed by the hardware or software? And if it is software would it be possible to add it (at least as an option) so it is accessible from VIX. :thumbsup:
Have a look in menu/setup/system/customize as im sure there is an option in those settings to change SNR from % to dB
No there's not. There are a few things to do with the info bar but not an option to change between dB and percentage. BTW in Nemesis it shows both (dB and %). What really gets me though is what does percentage relate to. 100% is a 100% of what?
No there's not. There are a few things to do with the info bar but not an option to change between dB and percentage. BTW in Nemesis it shows both (dB and %). What really gets me though is what does percentage relate to. 100% is a 100% of what?
Yes there is a DB option, its menu>setup>customise(Expert mode)>2nd page>Swap SNR in DB with SNR in Percentage on OSD....
But now that I've tried it doesn't actually change anything...i.e a channel is 89% Snr before I change the option and still displays as 89% after I change the option!
at best these figures to be used as no more than a rough guide to signal strength, no receiver in existence gives a true representation of signal strength, there just there to get you in the same ball park as your intended satellite network.
Yes there is a DB option, its menu>setup>customise(Expert mode)>2nd page>Swap SNR in DB with SNR in Percentage on OSD....
But now that I've tried it doesn't actually change anything...i.e a channel is 89% Snr before I change the option and still displays as 89% after I change the option!
Have you tried setting then re-starting Enigma 2?
at best these figures to be used as no more than a rough guide to signal strength, no receiver in existence gives a true representation of signal strength, there just there to get you in the same ball park as your intended satellite network.Nothing to do with signal strength, it's SNR, and the Dreambox reads pretty much the same as my 1200€ meter.
Anyway I've had a look and can't find that in my version of VIX (v2.0.3).
I think that option is only available on vix 2.2 upwards
I think that option is only available on vix 2.2 upwardsIs there any chance you could try it to see if it works, if you've got that version running? I don't really want to update my box only to find it doesn't work.
Rob van der Does
04-08-11, 18:02
He guys,
it's realy quite simple: the DUO-chipset doesn't support dB-read-out. So changing the setting makes no difference.
According to VU+ the UNO should be capable of both percentages & dB, but also on the UNO I see no difference.
yeh i noticed on the et i was able to get a db readabout but not on the duo
No there's not. There are a few things to do with the info bar but not an option to change between dB and percentage. BTW in Nemesis it shows both (dB and %). What really gets me though is what does percentage relate to. 100% is a 100% of what?
the dB measurement is a comparisson measurement, there is NO actual set scale for dB measurements, it starts from the amount of background noise, and compares that to useable information (signal) and is measured as a square of itself (it multiplies itsels each time) measured in increments of 3dB
what changes though, is where the useable comparison between background noise and needed signal begins.
a 3dB signal means that the needed signal is at the same level as the background noise, at 6db its twice as strong, at 9 db its 4x stronger than the background noise, at 12db its 8x, at 15db its 16x, and every 3db doubles the strength compared to background noise.
for satellite tuners, the VERY minimum is 65db on a clear sky day, so any onscreen reading that shows less than this, is showing false readings if you still have a picture. bigger dishes dont change this figure much, as even though the bigger area collects more signal from the satellite, it also collects more background noise as well
it's realy quite simple: the DUO-chipset doesn't support dB-read-outThat makes sense.
By the way if you had to choose between your ET5000 and Uno which would it be.
Rob van der Does
04-08-11, 20:47
By the way if you had to choose between your ET5000 and Uno which would it be.The UNO. More memory, VFD, nice housing, temperature controlled fan, room for internal HDD, scart, eSata
the dB measurement is a comparisson measurement, there is NO actual set scale for dB measurements, it starts from the amount of background noise, and compares that to useable information (signal) and is measured as a square of itself (it multiplies itsels each time) measured in increments of 3dB
what changes though, is where the useable comparison between background noise and needed signal begins.
a 3dB signal means that the needed signal is at the same level as the background noise, at 6db its twice as strong, at 9 db its 4x stronger than the background noise, at 12db its 8x, at 15db its 16x, and every 3db doubles the strength compared to background noise.
for satellite tuners, the VERY minimum is 65db on a clear sky day, so any onscreen reading that shows less than this, is showing false readings if you still have a picture. bigger dishes dont change this figure much, as even though the bigger area collects more signal from the satellite, it also collects more background noise as well
Right on Digidude,
I assume where S is signal power and N is noise power that the formulas are:
SNR (%) = S/N x 100
SNR (dB) = 10 log (S/N)
Therefore, as a mathematical genius I submit:
SNR (dB) = 10 log (SNR% / 100)
So it would be possible to make this calculation and display it, even though the direct read out of dB is not available. The calculation overhead may slow things down somewhat...
cheers
Right on Digidude,
I assume where S is signal power and N is noise power that the formulas are:
SNR (%) = S/(S+N) x 100
SNR (dB) = 10 log (S/N)
Therefore, as a mathematical genius I submit:
SNR (dB) = 10 log (SNR%/(100-SNR%))
So it would be possible to make this calculation and display it, even though the direct read out of dB is not available. The calculation overhead may slow things down somewhat...
Thus 3dB which is a ratio of 2 implies 66% signal and 33% noise.
and 6dB gives 80% signal and 20% noise
and 6.5dB gives 82% signal and 18% noise.
and 65dB gives ..... no noise to speak of.
Currently my satellite dish set up is yielding 49% which is a lousy 0.2dB but I'm still getting a picture.
Hmmm... my maths might be bullshit!
Anyone prepared to correct my formulas?
cheers
Due to the way dB is measured, there would be countless variables, from system to system, lnb noise figure, attenuation of cable and length of cable, external noise from other equipment connected to the same ring main, tuning of the receivers PSU, loads of things can change the dB reading. quite how this could be converted to a reliable percentage scale, im not too sure.
The signal intensity (power per unit area) can be converted to received signal power by multiplying by the square of the wavelength and dividing by 4π [Pi] (see Free-space path loss).
The dBm is not a part of the International System of Units and therefore is discouraged from use in documents or systems that adhere to SI units (the corresponding SI unit is the watt). However the straight decibel (dB), being a unitless ratio of two numbers, is perfectly acceptable.
You can use the unit of Watts to quantify the dB for transmitted signals, but the maths changes for received signals
Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt. To express an arbitrary power P as x dBm, or vice versa, the following equations may be used:
x = 10 \log_{10}(1000P) or, x = 10 \log_{10}P + 30\
and
P = 10^{(x/10)}/1000 or, P = 10^{(x-30)/10}
where P is the power in W and x is the power ratio in dBm.
there will ALWAYS be noise, and the more signal you collect with a bigger dish etc, the more noise you introduce into the system
This is turning into a classic as a satellite enginneer by trade I find this thread fasinating.
1. 3dB decrease in power will equal 1/2 power loss and 0dBw = 1 Watt therefore 30dBw = 1KW
2. All link budgets for satellite links actually use Eb/No as the measurment for link quality.
3. Noise in the system can be affected by a number of factors for instance you can raise the noise floor just by using the wrong paint on the dish.
4. The larger the dish of the same type the more gain you get.
5. The better the quality of the LNB the less noise you will have in the system.
I could get real technical here but as this is just for interest I am keeping it simple so use the shortest length of RG6 you can get away with use the best quality RG6 you can afford and buy the best LNB you can find, finally go for the largest dish you can fit on your roof :).
This is turning into a classic as a satellite enginneer by trade I find this thread fasinating.
1. 3dB decrease in power will equal 1/2 power loss and 0dBw = 1 Watt therefore 30dBw = 1KW
2. All link budgets for satellite links actually use Eb/No as the measurment for link quality.
3. Noise in the system can be affected by a number of factors for instance you can raise the noise floor just by using the wrong paint on the dish.
4. The larger the dish of the same type the more gain you get.
5. The better the quality of the LNB the less noise you will have in the system.
I could get real technical here but as this is just for interest I am keeping it simple so use the shortest length of RG6 you can get away with use the best quality RG6 you can afford and buy the best LNB you can find, finally go for the largest dish you can fit on your roof :).
paying the extra 15p/M for quality cable like CT100 or WF100 will improve things, i never use RG6
Rob van der Does
06-08-11, 10:53
1- A percentage will always be a very rough figure. But it is useful as long as you use the same receiver, for comparison between lnb's and for dish-alignment;
2- a larger dish will for sure provide a higher SNR-level. After all that's what a big dish is for........
The drawback is of course, that the opening-angel will decrease with dish-size, thus making a correct alignment more important.
Currently my satellite dish set up is yielding 49% which is a lousy 0.2dB but I'm still getting a picture.
Hmmm... my maths might be bullshit!Definitely something wrong with your maths. 50% SNR is somewhere between 8 and 9dB. That is according to a Satlook Color HD, and a Dreambox. Any difference between the figures yielded by the two devices is normally within 0.1 dB.
paying the extra 15p/M for quality cable like CT100 or WF100 will improve things, i never use RG6
So called RG6xx and so called CT100 can be:
* all copper decent braid
* All copper but braid too light is a problem when foil cracks
* core steel or aluminum with copper plating
* alumium foil & copper Braid (bad electrochemical corrosion)
* aluminium foil & tinned copper braid (bad electrochemical corrosion)
* plastic foil with metalisation and aluminum briad (yuch).
* Air core (best but easily damaged by kink)
* Old type foam (absorbs water badly and attenuates terribly)
* New type foam (no water absorption)
Variatons of
* Soft PVC outer (cracks in UV outdoor and porus to moisture)
* uPVC
* Trunk quality plastic, very stiff and mechanically strong, UV and water proof.
Unfortunately a lot of electrical wholesale have only 3 kinds of cable.
1) Skinny coax like RG59, except alumium and may or may not have foil. Like Chorus indoor cable in appearance.
2) So called low loss coax (maybe a choice of colours). very little braid and no foil. Virtually no screening effect.
3) Cable that might even be labelled RG6 or CT100, but more often simply has satellite printed on the drum. Copper plated steel or aluminum core, poor aluminum braid and plastic metalised foil.
The quad shielded RG6 from belden I have used in the past is as good as they come
If you want a real difference look at RG58 versus RG223 yes I know its 50 ohm.
I rest my point funny thing is I just let my master cabler licence lapse :)
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