Can someone explain BER.........?

guv69

OK, I'm aware that BER would indicate the dish is out of alignment. Have no problems with that, but I'm completely baffled by a few things.........

OK, I've just installed a 1m dish, and appear to trac the arc pretty well from 30W round to 42E.

I pretty much get 90% signal strength on most satellites - including 30W, 1W, 13E, 19E and 42E

Now you should note an interesting omission from the above.... 28E

I'm using USALS for positioning and have noticed I'm able to tweak the dish with a slight movement and the signal from sky does increase. This I assume indicates that the arc isnt being tracked 100%, since this movement should make it worse.

Now if the other outer satellites at 42E and 30W were suffering with weak signals, everything would make sense... but they are fine.

The strange thing... If I do make a slight movement, I am able to get the signal strength into the 90% - but in doing so, on some of the weaker channels, I then end up with BER. I'm completely baffled by this. Surely a stronger signal, should decrease BER, not increase it?

So, 2 fold questions....

Can anyone explain why an increase in SNR would introduce BER?

And on the bigger picture, how on earth is the only sat I have problems with is 28E? (I can even get Nilesat - albeit weak!) Whats the likely issue I need to address?

Forgot to say..... There isn't anything blocking the line of sight. the dish is roof mounted.... there isnt anything at all in the way. just realised this could have been given as a reason.... but its not the cause!

Cheers

Apogee

BER measures the number of errors in the digital stream and is the inverse of Quality. The higher BER, the lower the signal Quality.

If a weak digital signal is present among a group of strong signals, the weak one can be drowned out by intermodulation of the strong signals. In that case, introducing an attenuator can lead to an improvement in quality of the weaker digital signal. Alt. moving the dish slightly off peak, with lower overall signal level (SNR), would lead to a decrease in BER.
See page 12 of TeleSatellite 09/2006
magazine.tele-satellite.com/TELE-satellite-0609-eng.pdf

A second scenario would the channels on 26E. Many of the transponders share similar parameters as 28E e.g. MBC 11919, H, 27500 vs Sky 11914, H, 27500. The signal strength of the 26E channels are relatively weak. If you have a small dish with a large beamwidth and nudge a motorised dish away from 26E towards 28E, you can find the signal strength (SNR) appears to increase while the BER also increases i.e. bleeding of the 28E signal onto 26E.

A last example, mostly for C-band, would be the use of a dielectric plate for circularly polarised signals. Introduction of the dielectric significantly reduces the cross-polarization rejection for the linearly polarised signals and the signals on H can bleed through onto V - you can see it clearly on a spectrum analyzer. Again overall signal strength will increase but quality will decrease.

guv69

Apogee wrote: »

BER measures the number of errors in the digital stream and is the inverse of Quality. The higher BER, the lower the signal Quality.

If a weak digital signal is present among a group of strong signals, the weak one can be drowned out by intermodulation of the strong signals. In that case, introducing an attenuator can lead to an improvement in quality of the weaker digital signal. Alt. moving the dish slightly off peak, with lower overall signal level (SNR), would lead to a decrease in BER.
See page 12 of TeleSatellite 09/2006
magazine.tele-satellite.com/TELE-satellite-0609-eng.pdf

A second scenario would the channels on 26E. Many of the transponders share similar parameters as 28E e.g. MBC 11919, H, 27500 vs Sky 11914, H, 27500. The signal strength of the 26E channels are relatively weak. If you have a small dish with a large beamwidth and nudge a motorised dish away from 26E towards 28E, you can find the signal strength (SNR) appears to increase while the BER also increases i.e. bleeding of the 28E signal onto 26E.

I assume that introducing an attenuator, would affect the other satellites as well?

The silly thing here, I have manged to get these weaker channels on 28E (eg Real Live movies) working fine when I was messing about with dish alignment.

If it wasn't for the fact the tracking seems to be fine from 30W to 42E, I'd just put the problems down to poor alignment. Still think it is to be honest, but haven't a clue what I need to be doing to rectify.

Strangely, before I bought my new DM800, I was using my Channel master 1.2m and a sky dish with diseqc. I had exactly the same problem with Live Movies and a couple of the weaker channels. Yet the dish was fine and the signal received in my sky+ box proved that.

Doing my head in!!!

Nehaxak

Just a thought, what image/firmware are you using on the 800 ?
Been a long time since I used my own DM800 but noticed a fair few images about the place at that stage had incorrect settings for 28.2E - some had like 28.6 and 28.4 programmed in which frustrated the tuning process until I noticed what was going on :eek:

If I remember correctly, you can also make minor adjustments to satellite postions within the settings, rather than move your dish. If you're happy your dish is picking up everything else fine apart from 28.2E then I'd make adjustments firstly via the DM800's settings on that position.

Could of course also be your alignment slightly out, but just make sure firstly your DM800 settings are correct for the 28.2E position.

Couldn't recommend a good DM800 image though for you as it's been too long since I used my own.

guv69

Nehaxak wrote: »

Just a thought, what image/firmware are you using on the 800 ?
Been a long time since I used my own DM800 but noticed a fair few images about the place at that stage had incorrect settings for 28.2E - some had like 28.6 and 28.4 programmed in which frustrated the tuning process until I noticed what was going on :eek:

Nabilosat Black Hole V0.10 Enigma Head-May 2 2009, Image dev 2009-04-26

If I remember correctly, you can also make minor adjustments to satellite postions within the settings, rather than move your dish. If you're happy your dish is picking up everything else fine apart from 28.2E then I'd make adjustments firstly via the DM800's settings on that position.

Could of course also be your alignment slightly out, but just make sure firstly your DM800 settings are correct for the 28.2E position.

So using the "save position" option within the settings, will mean everything stays with USALS apart from this particular position save?

Nehaxak

guv69 wrote: »

Nabilosat Black Hole V0.10 Enigma Head-May 2 2009, Image dev 2009-04-26
So using the "save position" option within the settings, will mean everything stays with USALS apart from this particular position save?

Honestly I can't remember where exactly the setting is but yeah, you can change one positions settings, tweak it, minor adjustment of motor left or right and save that position. It won't (or at least shouldn't) effect any other positions. That assumes your elevation is also correct of course.

When you say you tweak the dish with a minor adjustment to get the 28.2E in better, do you have to adjust the elevation of the dish at all or is it just a slight movement left or right ?

If it's elevation then it's not the 800's fault, probably just the dish needs a very slight elevation tweak. If you are just tweaking the dish left or right to get 28.2E in better then you can use the DM800 to set this adjustment better, without effecting your other satellites tuned in.

Have you tried downloading one of the mutli satellite settings from the downloads section of that image to see if it makes things better for you ?

If I remember rightly, those black hole images where great for stability but were also one of the images released which sometimes had a quirk in the settings for 28.2E, setting them +0.4 for some strange reason.

Try the basic bog standard latest official dream image and see if that helps at all, at least to rule out the nabilosat image being at fault.

One of the better images I really started to enjoy with the DM800 before I had to move house and forgo my much loved hobby was the dual boot images that were just being released at the time. First (boot) half of the image sat on the box itself as the default, rest of the image sat on the USB drive. These images were very stable and had tons of features along with a load of downloadable (and frequently updated) multi-sat scans/lists you could download and use to start yourself off with. Took a little extra effort to set the images up but after that it was fantastic, load of lovely HD skins were also available for them along with tons of tested and stable plugins/addons.

guv69

Nehaxak wrote: »

Honestly I can't remember where exactly the setting is but yeah, you can change one positions settings, tweak it, minor adjustment of motor left or right and save that position. It won't (or at least shouldn't) effect any other positions. That assumes your elevation is also correct of course.

When you say you tweak the dish with a minor adjustment to get the 28.2E in better, do you have to adjust the elevation of the dish at all or is it just a slight movement left or right ?

Yeh, I mean using the "fine movement" control.

Its really weird though.... Just prior to posting, I had a little got to tweak. On Sky 1 HD, I never really got any signal change at any point until the signal dropped off at each end on the limit. I did the same with True Movies. The difference was quite a fair bit. On the normal position, the channel just breaks up. The signal is very low at about 69%. Moving West, the signal is up to 88%. I saved the position. Looking at Sky 1 HD - the signal strength hasnt changed. I cant understand how it could be like this, but it is - and its not H/V relevant either!

Have you tried downloading one of the mutli satellite settings from the downloads section of that image to see if it makes things better for you ?

To be honest, its a new setup. In fact the image was put on by the supplier. ATM, I wouldnt want to mess with it just yet. I've used images on my Eagle box before, but Ive been told the DM800 is a whole lot harder!

Nehaxak

The signal meter on the 800 I have to say is not very reliable at all, my opinion anyway, found it terrible compared to the last dreambox I had (DM7000) and had similar problems to what you've explained

Anyhow, when you're a bit more relaxed with the units config and how to install/setup images on it etc., plug in a decent sized usb pen drive (even 512mb will be fine), format it and use the "Barry Allen" addon to boot into multiple images. Saves an awful lot of hassles and you can always quickly boot into the internal firmware if anything goes wrong.

Person you bought it from should've just given you the default official image really and left the rest for you to install as the images from nabilosat et all can be troublesome. Always a good thing to only use the official image on the internal firmware/flash and only have other images on the USB drive, again using Barry Allen to boot up into whatever one you like.

guv69

Nehaxak wrote: »

The signal meter on the 800 I have to say is not very reliable at all, my opinion anyway, found it terrible compared to the last dreambox I had (DM7000) and had similar problems to what you've explained

Anyhow, when you're a bit more relaxed with the units config and how to install/setup images on it etc., plug in a decent sized usb pen drive (even 512mb will be fine), format it and use the "Barry Allen" addon to boot into multiple images. Saves an awful lot of hassles and you can always quickly boot into the internal firmware if anything goes wrong.

Person you bought it from should've just given you the default official image really and left the rest for you to install as the images from nabilosat et all can be troublesome. Always a good thing to only use the official image on the internal firmware/flash and only have other images on the USB drive, again using Barry Allen to boot up into whatever one you like.

OK. Many thanks for that. Once I get a bit of time, I'll have a dabble.