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joidevie is not online. Last active: 27/05/2014 17:45:20 joidevie



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Re: Astra 2E/2F Technical Thread
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I've never gone down the 'feedhorn' route? Is is a replacement 'insert' for an LNB, and is it a generic interchangeable upgrade? (ie would a particular type be needed for the 'Inverto SCD' for example..). Does the front of an LNB come off and you swap it over?

There seems to be a certain dish type (size) these work for as well...

Like you say, every db seems to make quite a difference..

PS The rain 'umbrella' or 'hood' has also been a revelation - no more rain drops on the LNB front which was blowing my signal every time it rained. I've heard an empty plastic bottle can help too   Wink [;-)]

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Quillan is not online. Last active: 07/10/2014 15:47:50 Quillan



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Re: Astra 2E/2F Technical Thread
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 joidevie wrote:
I've never gone down the 'feedhorn' route? Is is a replacement 'insert' for an LNB, and is it a generic interchangeable upgrade? (ie would a particular type be needed for the 'Inverto SCD' for example..). Does the front of an LNB come off and you swap it over?

There seems to be a certain dish type (size) these work for as well...

Like you say, every db seems to make quite a difference..

PS The rain 'umbrella' or 'hood' has also been a revelation - no more rain drops on the LNB front which was blowing my signal every time it rained. I've heard an empty plastic bottle can help too   Wink [;-)]

Neither have I so it is something new to learn. Basically your 'normal' LNB has a form of feedhorn built in but you can get better performance with a bigger feedhorn specifically when it comes to noise and interference between horizontal and vertical polarisation. So these things come in two parts, the LNB and the feedhorn. I kept seeing C120 being banded around and worked out that this is the 'standard' for the flange mount. Basically the LNB has a flange as does the feedhorn so the two can be bolted together and although it is advisable to buy the two as a matching pair you don't have to so they need a standard so the bolts line up on the flanges which is called C120.

The next bit I learned was that you need the right LNB for the dish as there are three types, Sky wide oval, offset and prime focus (or round). Then it gets a bit more complex because these techie guys also refer to offset dishes as round as well when to us they look oval shaped. That’s because with the offset arm for the LNB they actually present the signal as a round or circular pattern at the focal point. You can get prime focus LNB's to work on offset dishes and the other way round apparently but you loose out on signal quality and strength quite a bit. This apparently becomes even more important when you’re dealing with feedhorns as far as I understand it. So my current problem is to find a feedhorn and LNB that will specifically work with my shape and sized dish which is basically a 130cm although in reality it is 134 x 127cm but at the focal point it is presented as a 130cm round dish.

I am going to phone a couple of guys up in the UK tomorrow firstly to see if how I understand it is correct and secondly to get some ideas on the best LNB and feedhorn to buy for my dish.


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Danny is not online. Last active: 20/10/2014 12:56:53 Danny

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Re: Astra 2E/2F Technical Thread
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plenty of good general advice/explantion here
http://www.satellitesuperstore.com/feedhorns.htm#advice

The main general advice is Dish size is everything. Woot! [:-))]Stick out tongue [:P]

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Quillan is not online. Last active: 07/10/2014 15:47:50 Quillan



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Re: Astra 2E/2F Technical Thread
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And he is of course right. That said he goes on to say that is some cases (and he quotes mainland Spain and the Spanish islands) fitting one has made the difference between some channels getting pixels and not getting pixels. He even goes on further to say that in some cases it has pulled in the signal when there was none before. Seeing as we only have a problem with one or two channels at particular times of the day I thought it might be worth a try especially as the next size up dish is considerably more expensive than the one I have now.
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"When did I realize I was God? Well, I as praying and I suddenly realized I was taking to myself." Peter O'Toole 1932 - 2013
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PaulT is not online. Last active: 11/09/2014 06:28:20 PaulT

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Re: Astra 2E/2F Technical Thread
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Past week or so the reception on an 80cm dish changed from being OK most of the time to being very blocky at times or NO SIGNAL. Just installed a 130cm dish and we now have not just good quality SD channels but also HD channels.

The site that Q referenced earlier says the important things are, dish size, dish size and dish size.
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AnOther is not online. Last active: 15/10/2014 08:06:36 AnOther



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Re: Astra 2E/2F Technical Thread
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 Quillan wrote:
A good LNB is equally important as you are also probably aware.


But what is a good LNB ?

Lowest noise figure you say - think again !

http://www.satcritics.com/sc_tech_lnb.pdf

And those who were seen dancing were thought to be insane by those who could not hear the music.
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Quillan is not online. Last active: 07/10/2014 15:47:50 Quillan



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Re: Astra 2E/2F Technical Thread
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A good LNB performs better all round than others and of course to get better you pay more money which is what he is saying when he compares different LNB's on pages 6, 7 and 8.

If you lived in the UK most if not all the LNB's meet the standards he mentions even though they are now out of date and he should be looking at the Astra 2 specification rather than the old, to be retired, Eutelsat satellites.

You also have to keep in mind that the maximum disk size specified is 60cm for the Astra satellites servicing the UK after which your on your own and as we have seen there are no guaranteed results. Somebody 15km away can get excellent reception on a 100cm dish where as you could be struggling with a 130cm one. When you get to this level it is worthwhile looking at a better performing LNB like the Invacom which has definitely helped people who have been having reception problems.

In theory it is all down to the dish size and won't find anyone who disagrees. You should be able to any standard LNB but just increase the dish size till it works. However a good LNB can effectively add a couple of cm to the size of your dish and perhaps when used with a feedhorn of good quality you can make a 130cm dish perform the same as a 140cm. It all comes down to the price of the dish and practical side of mounting it. A 130cm dish will cost around 130 Euros, move up to a 150cm dish of reasonable quality and your looking at about 600 Euros, should you need to go even bigger to say a 180 cm dish you're looking at a grand. Then there is the installation cost, a 130cm dish will bolt to the side of your house, move to a 150 and 180 and you are looking at constructing a ground mount on a concrete pad which adds serious cost to the installation. So if you're on the edge of reception and suffer from a bit of pixelation now and again or you only need light rain to lose your picture it may pay to look at a better quality LNB and even a feedhorn.

One thing I didn't see him mention is length of cable. As he says you want the right amount of gain but if you have a long cable run due to where you can mount your dish even with a quality cable you may need a high gain LNB so that when the signal arrives at your decoder it is at the right level with maximum signal quality and lowest noise levels.

Other than that it is an excellent bit of work with some simple explanations which certainly helped me as I am sure it will others.


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"When did I realize I was God? Well, I as praying and I suddenly realized I was taking to myself." Peter O'Toole 1932 - 2013
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Jako is not online. Last active: 12/08/2014 10:12:49 Jako

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Re: Astra 2E/2F Technical Thread
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With the new 8PSK transmissions the phase noise is more important than previously. If the SD channels are ok, but the HD channels are not and the LNB is new it might just be a production 'glitch'. According to the skyinmadrid website the quality control at Inverto's is poor and the consumer might end up with a mediocre LNB.  Their advice is to use an Invacom LNB in fringe areas and a reader comment of "Gordon, Frejus, France" seems to confirm this:

"Re your news item of March 15th where you recommended Invacom LNB's.
As Astra 2E came into service I re-cabled my 1.2 meter dish and bought a new Sedea LNB. However I was still losing my 'local' BBC1 and all BBC HD channels from tea-time onwards. Following your rercommendation I bought an Invacom twin LNB from Amazon France for €43, and the difference is remarkable.
I can now get ALL channels both SD and HD at all times of day and night, the signal strength on my weaker feed has gone from 40% at best time of day, to 70% for Quality, and 85% for strength. I live in a forested area in South Eastern France."

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