45 replies to this topic

[jpuigs]

Xtrend ET 8000.

All transponders show AGC level of 37 %, regardless of SNR level

[Erik Slagter]

AGC and SNR are not related. What are you expecting?

[jpuigs]

I'm expecting different values.

Since a few days ago, I got AGC values from 60 to 95%, different for each channel (transponder) and they were changing slowly (+ - 2%) but constantly.

Now, EVERY channel has 37 % all the time,

[jpuigs]

I've made more tests.

I've flashed a backup which I had from last year, and AGC value works fine, each transponder has its own value.

I've gone back to today's backup, and now AGC is stuck at 37% in all transponders again.

So there is a bug anywhere.

Look at the screenshots.

Same  frequency, different images.

 

 

Correct values:   agc_ok.jpg   57.26KB   15 downloads

 

 

Wrong values:   agc_ko.jpg   56.56KB   14 downloads

 

 

[Erik Slagter]

There is no "correct" AGC value. What do you think to learn from the AGC value?

[littlesat]

I'm already thinking for years to simply remove it.... Is doesn't indicate any concrete thing.... But when we remove it, this forum get stormed that users are missing this non valuable information.

 

The only thing that is concretely valuable is the bits that are received falsely.... so the BER.... This is also the only way to indicate the signal quality which can be compared between different receivers. The SNR in dB is still something that just tries to do that, but is far from ideal.

 

At this moment for Enigma2 boxes there does not exist a driver that gives that information... Far way ago in the Enigma1 time on a DMM7K box I did add it to E1 as that time we could directly manipulate the tuner as it was always the same tuner... I also added that time an algorithm that adjusted the AGC to optimize the BER... That makes the tuner more sensitive at that time... But since Enigma2 this was not possible anymore

Edited by littlesat, 29 May 2016 - 09:39.

[Rob van der Does]

'AGC' gives you some information in the first step of a dish setup. But that's all, and in most cases a mobile readout (Android/IOS) is much more handy for that.

So indeed: why not delete it from the GUI? Will prevent people from misinterpreting it as well

 

IIRC there are some USB-tuners (Sundtek?) that do provide BER; but not sure if this is the value before correction. If not, it isn't useful either.

[jpuigs]

OK.....

But let's change the question.......

Why I had AGC different values in each transponder, and  since some weeks ago I have the same fixed value everywhere ??  Driver change ? enigma 2 change ?

 

The BER value is not usefull, it gives information after correction, the AGC value was usefull, becauseit wassimilar to a BER before correction.

[arn354]

Nothing changed in Enigma2. Probably new drivers/kernel of et8000.

[athoik]

You can use dvb-fe-tool and femon to read values from tuner directly using dvb api.

You need to install v4l-utils and femon to get tools. Use the correct adapter and frontend parameters to those utils.

That will shown us if drivers return dummy values.

Edited by athoik, 29 May 2016 - 12:55.

[Rob van der Does]

Why I had AGC different values in each transponder, and  since some weeks ago I have the same fixed value everywhere ??  Driver change ? enigma 2 change ?

Driver change. Apparently the last drivers are not capable of supplying AGC-values.

But it's cosmetic; what would you want to learn from a correct value?

[Erik Slagter]

The AGC value is 100% obtained from the driver and copied verbatim. That also mean that the actual meaning of the value is also completely imposed by the driver. If someone has complains about the AGC value, they can report it to the manufacturer directly.

 

But besides that, AGC is both meaningless and completely unsuitable for comparison between different tuners. For one,  AGC should decrease when the signal gets stronger. In practise most (!) tuners report a value that increases on stronger signal. Or, and that's in the majority of the cases, they report a value that's more or less meaningless.

 

So okay, can we now stop the endless AGC discussion. Ignore it and everybody's happy.

[jpuigs]

Erik, I know it's cosmetic, and of course that two different tuners show different values.

My dreamboxes, as you said, have decreasing values when signal gets good and strong, and Xtrend receivers have the cokpletely opposite behaviour, I know it, and I give it real interpretation based on each receiver.

(The DVB-T Tuner on my ET8000 shows always 0 value on DTT channels, but as I've always seen the same value, I don't worry)

 

The real usage I can get it from AGC value, is to know if I have a problem with any dish.

If I know I have an AGC value of 75% since ages.... and one day I see it has heavily decreased, I'll check wether the LNB has a hole (and has water inside it), the diseqc is broken down, the dish has moved due to a heavy wind, etc....

It's only a fast way to see if everything continues to be right.

[littlesat]

The Agc does not even tell nor indicate the strength of the signal...

[Dimitrij]

This is very important value.

For example:

ET8500

LNB 36E --> 20 meters of cable --> Agc 81%-85%

At one point, the value was Agc 30%-40% --> reason --> cable was broken in it is exposed to water

[mrvica]

seems that AGC is not just related to satellite Equipment
https://en.wikipedia...ic_gain_control
this could be interesting too
https://en.wikipedia...-to-noise_ratio

[littlesat]

The only real factor that depends and is measurable comparable is ber and no receiver driver does offer this.

[athoik]

Os mini offers BER, but i don't remember what BER it offers (post ber i think)

[littlesat]

Sorry indeed one ber is given... But I mean thr other ber.

[Matrix10]

The AGC value is 100% obtained from the driver and copied verbatim. That also mean that the actual meaning of the value is also completely imposed by the driver. If someone has complains about the AGC value, they can report it to the manufacturer directly.

 

But besides that, AGC is both meaningless and completely unsuitable for comparison between different tuners. For one,  AGC should decrease when the signal gets stronger. In practise most (!) tuners report a value that increases on stronger signal. Or, and that's in the majority of the cases, they report a value that's more or less meaningless.

 

So okay, can we now stop the endless AGC discussion. Ignore it and everybody's happy.

 

Eric AGC should not decrease when the signal gets stronger.

But increase.

 

Which means, with stronger signal , higher AGC
whose function is to reduce the strength of strong signals to the input of the receiver to minimize the possibility of creating harmonics and other additional products in front of the receiver.

 

You are right.

AGC has no practical value for the user and antenna measurements.