Comparing sensitivity

[Stejc]

Hi

What would be the best way to compare sensitivity of two tuners? I have been looking at the SNR values in Crazyscan but in comparing my TBS QBOX 5922 to the TBS Pro 6903, the 5922 seems to be by .1 or .2 more sensitive.

Can this be right or could it be just the way the tuners are reporting back to the software? The 6903 cost about 4 times as much so I would have thought the tuner would be more sensitive.

Thanks

 

[blademedia]

Best way would be to keep moving the dish very slightly until picture pixelates, then try other receivers without moving the dish,

I have a £18.99 box with a more sensitive tuner than my TBS 5925

 

[Tururu]

The best and most real test.
The meters in the equipment, can be retouched to measure more or less.
The VU + DUO2 results that it badly measures the signal, with the last drivers solve it, it measures like the other VU + equipments, with the new ones I gained almost 2dB, 10% more signal, thanks.
----------------
La mejor prueba y mas real.
Los medidores en los equipos, se pueden retocar para que midan mas ó menos.
El VU+DUO2 resulta que mide mal la señal, con los ultimos driver lo solucionan, mide como el resto de equipos VU+, con los nuevos gano casi 2dB, 10% mas de señal, se agradece.

Best way would be to keep moving the dish very slightly until picture pixelates, then try other receivers without moving the dish,
I have a £18.99 box with a more sensitive tuner than my TBS 5925

As indicated by blademedia, I moved the antenna until I lost the signal in a DreamBox800S-HD as we can see, in that position connect the VU + DUO2, mark the only error when pixelar 3 times during 20 minutes of test, the sound is not heard.
------
Como indica blademedia, movi la antena hasta perder la señal en una DreamBox800S-HD como podemos ver, en esa posicion conecte el VU+DUO2, marque el unico error al pixelar 3 veces durante 20 minutos de prueba, el sonido ni se entero.


Una foto 3.5dB, DB800 señal/SNR 21%. (Cantante: Adele)

Una foto Vu+ señal/SNR 32%.

 

[Channel Hopper]

Hi

What would be the best way to compare sensitivity of two tuners? I have been looking at the SNR values in Crazyscan but in comparing my TBS QBOX 5922 to the TBS Pro 6903, the 5922 seems to be by .1 or .2 more sensitive.

Can this be right or could it be just the way the tuners are reporting back to the software? The 6903 cost about 4 times as much so I would have thought the tuner would be more sensitive.

Thanks

Final receiver specification and cost has absolutely no correlation to the tuner / demodulator used.
Additionally many models will appear deaf owing to default firmware that is not entirely compatible to the hardware it is coupled with.

 

[Terryl]

The best way is to use a calibrated RF signal generator, setup for a 75 ohm inductance, this way you know exactly how much signal is getting to the tuner.

What we used was a RF generator connected to a calibrated transmit antenna, (you know the exact gain of the antenna at that frequency) that way you know one part of the formula (X+Y) and we set the antenna at an exact distance from the dish, LNB and receiver under test, this gives you a calibrated input signal.

You can delete the antenna and LNB and use the frequency of the down-converted IF signals for the transponders, (10200 MHz to 11250 MHz -minus the LO in MHz = IF signal) so for a given IF signal at lets say at -50 dBm into the tuner equals 75% on one receiver (guessing) and 78% on another, then you have a direct calibrated comparison on a known signal.

 

[jeallen01]

And then there is the sample-to-sample variation issue for a wide range of possible reasons - components, assembly personnel, "day of the week", quality assurance thoroughness, etc.

For example: there used to be a long running discussion on LNB sensitivity, with known significant variations in the performance of units all specified as being "0.1dB" whereby they were sometimes even worse than some 0.2dB or higher units. Don't forget that people writing the advertising specs will always try to put their products in the best light as compared with those from their competitors - but generally without stating whether the measurements were taken under comparable test conditions.

So, it's always going to be a bit of a gamble with kit working "right on the edge" of its performance limits - and the best you can probably do is to look for product specs and reviews, and ask for opinions on particular equipment, as well as very carefully adjusting your particular dish/lnb motor setups (unless of course you have the capability and time to carry out back-to-back tests of the possible candidate receivers).

Also, when a very weak transponder signal is right on the "limit" of readability, the weather, or other atmospheric/stratospheric/solar conditions, can come into play for either/both the uplink or downlink signals, and there is also the "satellite orbital wobble" issue which can slightly deflect the beams, and one/many/all of these factors can affect whether the signal is receivable or not at a particular time.

 

[blademedia]

My test are done on the same lnb same make of cable, both runs the same length, monitoring two TV's at the same time, whatever receiver/card maintains a lock has a better tuner,

Signal levels mean nothing there not even a guide most of the time on most boxes, its the lock that counts. I could connect two different boxes up now to the same lines mentioned and see a 35% difference in signal level from one box to the other.

 

[jeallen01]

My test are done on the same lnb same make of cable, both runs the same length, monitoring two TV's at the same time, whatever receiver/card maintains a lock has a better tuner,

Signal levels mean nothing there not even a guide most of the time on most boxes, its the lock that counts. I could connect two different boxes up now to the same lines mentioned and see a 35% difference in signal level from one box to the other.

bm
Although I don't have the facilities to replicate your setup, I pretty much agree with your comment as above. I was simply pointing out the to OP that comparing the "quoted sensitivity" of various receivers (as opposed to their lock-up capabilities) has a whole lot of possible pitfalls that might not be obvious at first, or even second, glance, especially when looking at performance at the sensitivity threshold - and you, of course, are pointing out to him the equally, if not more, critical lock-up capability issue.

BTW: w.r.t. the Freesat 7D (the £18.99 receiver), I found that the Opensat V8S was pretty much it's equal in terms of lockup on 31.5W, whereas the Freesat V8 Super would not lock up any channel on that bird (and so that receiver went back to the supplier).

 

[blademedia]

bm
Although I don't have the facilities to replicate your setup, I pretty much agree with your comment as above. I was simply pointing out the to OP that comparing the "quoted sensitivity" of various receivers (as opposed to their lock-up capabilities) has a whole lot of possible pitfalls that might not be obvious at first, or even second, glance, especially when looking at performance at the sensitivity threshold - and you, of course, are pointing out to him the equally, if not more, critical lock-up capability issue.

BTW: w.r.t. the Freesat 7D (the £18.99 receiver), I found that the Opensat V8S was pretty much it's equal in terms of lockup on 31.5W, whereas the Freesat V8 Super would not lock up any channel on that bird (and so that receiver went back to the supplier).

Hi jeallen, your input was very useful and based on facts, I wasn't disputing any of it because its true, I was just pointing out how I do my testing, I would recommend the way I do it but as you say not everyone has this arrangement, reason I suggested swapping boxes,

High signal levels are a good selling point/money making racket, look through the old Technomate posts from years back, though there receivers was good way back when sensitivity was not the best, but costumers was happy seeing 100% levels most of the time and was a good selling point,

 

[jeallen01]

bm

I think we agree! When I was doing those comparisons, I did use the box-swapping approach - one receiver sat literally on top of the other and everything else was the same.

 

[Tururu]

bm
I think we agree! When I was doing those comparisons, I did use the box-swapping approach - one receiver sat literally on top of the other and everything else was the same.

In my case, just change the antenna cable, the rest is duplicated/En mi caso, solo cambiar el cable de antena, resto esta duplicado.

Here we are playing with the equipment and the quality of the receiver's tuners, if we look at the data, from one photo to the other I put, only 7 minutes, which later on the satellite dish connection and take the photo.
February 7, 2014 20:13:05 ===> February 7, 2014 20:20:37.

Better comparison of the quality of the tuners at zero cost, I do not know.
If you want to do well, nothing better than a signal generator directly to the receiver tuner (with calibration a day, of course), years ago very expensive equipment from € 18,000 to € 36,000, used to adjust the tuners of the equipment in the Work, are now cheaper.
------------------------
Aqui estamos jugando con equipos y comparar la calidad de los sintonizadores del receptor, si miramos los datos, de una foto a la otra que puse, solo pasaron 7 minutos, lo que tarde en cambiar la conexion de la antena parabolica y hacer la foto.
7-febrero-2014 20:13:05 ===> 7-febrero-2014 20:20:37.

Mejor comparacion de la calidad de los sintonizadores a coste cero, no se.
Si lo quieres hacer bien, nada mejor que un generador de señal directamente al sintonizador del receptor (con la calibracion al dia, claro), hace años equipos muy caros de 18.000€ a 36.000€, usados para ajustar los sintonizadores de los equipos en el trabajo, ahora son mas baratos.

138M--4.4G SMA signal source,generator,simple spectrum analyzer +Tracking source

 

[Terryl]

Most (if not all) satellite receivers use an off the shelf tuner module from another supplier, this could be a stand up soldered in place or plugged in module, or one that is integrated into the main PCB as a drop in sweat soldered in place.

All these are factory tested in bulk, and use what is called an RSSI* voltage from the tuners AGC* circuitry to see if they meet specifications.

A known signal at several different levels (low medium high) is applied to the module under test, The RSSI voltage must fall withing a certain percentage and range to pass the test.

It's this RSSI voltage that is sent to the systems processor and converted by an internal A to D and by software to give you the "S" reading on your receivers display.

The best way to test for direct sensitivity is to find this RSSI voltage output from the tuner and compare it to a second receiver of the same make/model, this way your going around all the conversions and getting a direct reading.


*RSSI= Receive Signal Strength Indication.
*AGC = Automatic Gain Control.