What do the T4 Signal Strength & Quality Indicators Measure

[jplouis]

I recently had some reception issues with the T4 - now sorted - splitter in the roof problem

However on the way I found difficulty interpreting what was being reported by the T4 - I've searched the forums, but some clearer explanation of the signal quality measures would be appreciated.

After my hardware fix I have around 70 dBuV, measured independently, into the receiver, so reasonable signal level.

Using Webif to catch the numbers I get [These correspond to those reported by the T4 display, but where no indication is given as to what the two measures reported actually are? ]

Tuner Type: DVB-T Tuner Number: 0 Tuner Signal Quality SNR: 100
Tuner Signal Quality SNR_DB: 100 Tuner Signal Power AGC: 26 Tuner Bit Error Rate BER: 0

So bit error rate BER = 0 : Great, easily understandable

SNR = 100 : I assume this means Signal = 100 x Noise?? Or is it some other scaled? or percentage? value - if so what?

If SNR = 100, I would expect SNR_DB = 10 * LOG10(SNR) = 20 dB for voltage [or 40 dB for power] So I'm not sure what is being reported here?

Signal Power AGC = 26 : This appears to be related to some form of automatic gain correction?
Is it measuring the amount of gain applied to the signal? or the power of the incoming signal from the aerial [70 dBuV in my case]?
What are the units for this measure and what would be an acceptable reception threshold using this measure?

A clear understanding of what these signal strength & quality measures were, and whether they were acceptable was what I wanted but could not glean from my T4 display - I'm sure a lot of other T4 owners would like this information more clearly explained as well.

Thanks

John Louis

[MrQuade]

A clear understanding of what these signal strength & quality measures were, and whether they were acceptable was what I wanted but could not glean from my T4 display - I'm sure a lot of other T4 owners would like this information more clearly explained as well.

I wouldn't think too hard about it. The numbers are "magic" and can even change with different drivers.
They are there to simply be treated as a measure of strength and signal quality that is *relative only*. You can compare the values between the four different tuners, or compare the values from your T4 to someone else's T4, but they are somewhat meaningless beyond that (ie. you can't even compare the values that you'd see on a T2, T3, U4 or V2).

[prl]

It's generally unclear exactly what any of those numbers represent (including BER).

The signal strength figure is usually indirectly measured by calculating it from the tuner's setting for the AGC gain. The lower the AGC gain, the higher the signal level.

The SNR is again derived in the tuner, but I'm not sure how.

In general, those two are not comparable between different tuner models (and hence between different Beyonwiz models), and some USB tuners don't report them at all.

I think that the BER is the rate of errors detected in the Reed-Solomon forward error correction, and that it includes both corrected and uncorrected errors. What I'm less sure of is the period over which the errors are counted (but 0 is always excellent). I don't think it includes errors corrected by the lower-level convolution code in the signal.

Only the Signal strength and SNR percentage are displayed in the pre-loaded skins. IanSav's OverlayHD skin also shows BER. Ian's BER display flashes if the BER is over 375, but I don't know how he arrived at that threshold.

[dRdoS7]

Hi,

I think the signal strength & quality meters are the like the piece of string used for weather forecasting, only prettier.

I don't remember any device, except for a dedicated meter, that gives actual readings. If we knew what they were, how would it help? Can they tell you if it's cabling/connectors/antenna/transmitter that's the problem?

dRdoS7

[jplouis]

Thanks for the responses - I get the picture [no pun intended] - I'll just stick with my external signal strength meter for troubleshooting reception problems.