Good agc/ weak snr

[rinaldi1]

Hi guys,
on astra 19.2 and hotbird my agc is good (roughly 80% on most transponders) but snr on many is quite low (50/55 %) , is this likely to be the skew on the lnbs that's causing this? If so, where can I find out the correct angle to set them to? Many thanks. ps fixed dish with triax multi lnb bracket

[nml52]

Re: Good agc/ weak snr

Hi guys,
on astra 19.2 and hotbird my agc is good (roughly 80% on most transponders) but snr on many is quite low (50/55 %) , is this likely to be the skew on the lnbs that's causing this? If so, where can I find out the correct angle to set them to? Many thanks. ps fixed dish with triax multi lnb bracket

It all depends on what dish size, and the low ones are they v or h you need to be more specific. For example what satellite is the dish centred on, in terms of skew if all the vertical ones are down you know which way to turn the lnb, you wont find angles for a multi lnb bracket you have to do it yourself.

Hope this helps. nml

[aplok]

Re: Good agc/ weak snr

here is a interesting post for you:

Dish adjusting with e2 plugin

http://www.satlover.eu/forum/installation/51378-dish-adjusting-with-e2-plugin.html#post293286

[peremacedonia]

Re: Good agc/ weak snr

Try to turn lnb left and right and see the result

[Mobley3]

Re: Good agc/ weak snr

Unless you are using a very small dish then your Q reading are certainly low, when I was using a Multi Lnb set-up with 1Mtr dish in Ireland I used to have S & Q readings above 85% on both of these sats, if memory serves me correctly I used to have the skew set on both Lnb's roughly around the 7oclock position. If you are happy that your Dish is beamed correctly then you should also try moving the Lnb's forward and back in their holders to focus them on the Dish

Regards Mobley3

PS. The 19E Lnb should also be slightly higher than the 13E one

[rinaldi1]

Re: Good agc/ weak snr

Many thanks for the replies. I have an 80cm dish which should be plenty big enough I think. I can't move the lnbs longitudinally but will try rotating them if it ever stops fecking raining here in Glasgow!!

[Mobley3]

Re: Good agc/ weak snr

Why can you not move them ? there is usually about an inch of play on the throat of the Lnb, is it something to do with the design of the mounting? even a quarter of an inch may make a difference, it is about illuminating the full surface of the dish without getting over-spill which would add noise.

Regards Mobley3

[rinaldi1]

Re: Good agc/ weak snr

Why can you not move them ? there is usually about an inch of play on the throat of the Lnb, is it something to do with the design of the mounting? even a quarter of an inch may make a difference, it is about illuminating the full surface of the dish without getting over-spill which would add noise.

Regards Mobley3

As far as I remember the lnbs I have fitted have very narrow necks...I'll have to check. On many t/ponders my agc is up at nearly 90% so hopefully rotating the lnbs slightly will sort out the snr issues, thanks again for the advice

[fandm]

Re: Good agc/ weak snr

Like mobely3 said in his first post you need a skew to 7 o'clock, unless something is wrong with your lnb.
Also your profile says uk so you should have a signal of 85%.100% quality

If you have easy accsess to your dish, take the sat box and a small tv to your dish then do your adjustments. skew inc and az but don't try this if you have to go up a ladder.

[kalpikos]

Re: Good agc/ weak snr

Hello rinaldi1

The dish you have is a rather small dish , it's not a big dish.
Depending on the satellites you want to get, your dish could be small in most cases.

As about your problem,
first, you have to find if the dish correctly alignment to the centered satellite and then start to check one by one the other lnb.

As @Mobley3 said, you have to find a way to move them slightly in order to find the perfect position.

After that, you have to turn each lnb left or right in order to find the best signal.

[pan1300]

Re: Good agc/ weak snr

hi rinaldi1

extra tip on the above: first find a sat with a strong transponder, and then finetune with a weak one - more info can be found here: http://www.sl-forums.com/forum/satel...nsponeder.html

[Satphoenix]

Re: Good agc/ weak snr

Perhaps a simple technical reason. What is the roll off factor of the lower transponders? Is it 1,2 or 1,35 (the more the better!)?

Normal SD-Transponders have 1,35 with qpsk and the typical hd- transponders have 1,2 (8psk).
8psk is not so easy to recieve than qpsk which means the snr is a bit lower.

[kalpikos]

Re: Good agc/ weak snr

I forgot to mention that the alignment of the dish must ne done while you are watching your tv in order to achieve the best signal.
Moreover you can use a laptop close to you when you will align the dish.

[digicon]

Re: Good agc/ weak snr

Just to Clarify the AGC Automatic Gain Control is done by the receiver's tuner so as not to overload the Tuner itself this is basically the power of the satellite signal and if too much the receiver tuner will either increase or decrease the amount.

SNR is Signal to Noise Ratio in other words the actual 1010101010101 bits of the picture and audio and this needs to be as high as possible out of say 10 bits sent only around 506 are the actual A/V the other 4 are backup in case of BER or any other anomilies.

So to clarify forget all about AGC and concentrate on the SNR alone as this is what will give you a steady and complete picture

[Satphoenix]

Re: Good agc/ weak snr

Perhaps for understanding you can compare the not-so-good signal with "music" on an old audio-tape.
This tape always has a backgroud noise. If the "music-signal" is not strong enough, the complete signal is made louder, but this also makes the background noise louder too so that you have a signal with normaly loudness, but the soundquality is "not the best" because of the (now) louder background noise.
That's the reason why the original signal quality (here the snr) is so important to have errorfree receiving.