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Reception tips

2old4this

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#1
Here are a few tips for best reception of satellite broadcasts. I invite professionals or keen hobbyists out there to add to the list.
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- use the lowest noise LNB you can get (but beware: some LNBs quote average noise rating, some quote minimum, and they rarely say which...

- rotate LNB to optimum skew position . Optimum angle depends on the satellite and your location: see (eg) the SMWLINK program from Swedish Microwave site - links elsewhere on this board.

- use only high quality sat co-ax cable (don't use standard TV coax)

- ensure there are no breaks/connectors in the co-ax between LNB and receiver

- keep the co-ax as short as possible (any longer than 25m and you should consider installing an in-line signal amplifier)

- ensure there are no sharp bends in the co-ax (different cables have different ratings indicating the severest curvature they can tolerate without signal degredation)

- avoid any possibility of water ingress by (a) not damaging the co-ax sheath anywhere along its length and (:cool: masking the connector at the LNB with waterproof mastik (or similar).

- use solid dish rather than mesh - solid is at least 20% better than a mesh dish of same size

- use a Gregorian dish (those with a sub-reflector) if size is a limiting factor - a Gregorian is 20% better than a normal offset dish of same size.

- check alignment of dish is optimal, using preferably a signal meter or else the "wet-towel method". The latter entails masking off progressively more of the dish using a wet-towel (water absorbs microwaves) so that the reducing signal arriving at the LNB necessitates a finer dish adjustment.

- avoid any intervening objects (trees, windows...). And beware if you have an offset dish and think it is neatly aligned to a gap between/under some trees... a prime-focus dish has the LNB in the middle, but an offset dish has the LNB at the bottom, so receives a signal that comes in from the top (reflected downwards to meet the LN:cool:. So such a dish might appear to be "looking" directly at a blank bit of sky, but actually needs a clear view to the bit of sky ABOVE where it seems to be pointing (ever wondered why when watching sats close to the horizon the dish seems to be pointing at the ground?)

2old
 

rolfw

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#2
I think that covers nearly everything 2old, the wet towel method is most effective when used with an analogue receiver as it induces sparkles but not quite so effective with digital. One of the biggest problems that I've seen on installations is cable clips being hammered in too hard and denting the cable.

One other point that I've noticed is that some older universal LNBs are not stable enough for some digital signals, although they can give an acceptable signal on installation they can deteriorate in temperature extremes.

Rolf
 

p

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#3
Its a bit of a silly one, but happend to me.

Keep the dish clean, from dirt and bird crap.

Got a loss of picture once on analougue, checked all conections, couldn't figure it out then found a bird had left a present on the end cap of the LNB!

Phil
 
V

ViperSan

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#4
I can go one better than that 'p'
totally lost reception on my motorized 1 mtr dish ...couldnt work ou what was wrong ...but suspected a faulty lnb.
Got the ladders out and removed the lnb (universal type with c120 open ended feedhorn,prime focus)..
nearly fell off the ladder laughing when I realised what had happened.
It seems some bird had mistaken the open feedhorn for its siblings hungry mouth...and had been feeding it.
It contained dried up worms,chewed up bread pellets....and of all things a sticky toffee...
lol
 

w hole

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#5
Hello All

This is a great summary of tips, and perhaps it should be a feature of the FAQ's with updates by 2Old of any tips he thinks worthy of inclusison.

It has raised a thought in my poor old brain.

The Lidl's cheap analogue set up advertised recently, and mentioned on a seperate thread, seemed to include a Solid Dish.

My current dish is 70cmH x 65cmW and is of the mesh variety.

How much would I improve my reception by getting the Lidl's kit and using the dish which was described I think as solid steel.

BTW did anyone find out about the LNB, was it dual or sigle.

[Sorry if I have 'crossed the threads' of the two topics, and do feel free to reply to the Lidl's part of this on the other thread.]

Kind regards

W Hole
 

2old4this

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#6
More points for consideration:

- mesh is said to have only 80% of the gain of a same-sized solid. However, this rule-of thumb originates from the time that the most common form of mesh dish was the huge "DIY" types used for C-band. That they would have a lower gain is more likely due to their imperfect form (typically being segmented, rather than smoothly curving) than to the intrinsic quality of mesh vs. solid. Logically, if the mesh surface was perfectly formed and the gaps smaller than the microwave wavelength ("micromesh"), there should be no difference.
Any professionals out there that can clarify...?
In the meantime, read this: http://www.drdish.com/features/mesh.html

- a solid picks up more wind and so is more susceptible to being blown out of alignment in storms.

- so long as the dish is correctly formed and the surface is smooth then the underlying metal (steel, aluminium, whatever) is not of significance (but note: there must be a metal layer somewhere; it is the metal that reflects the microwaves). However, dents or a rough paint job will cause incoming signals to be reflected away from the ideal focal point, so reducing gain.

- The form of both a prime-focus (as used, eg, for C-band) and offset dish (LNB on an arm at the bottom) must be a parabola. However, the degree of curvature is not the same. This link explains it: http://www.mlesat.com/antennas.html
If you were to misuse an offset dish as a prime-focus dish by rigging up your own central LNB mount you would not get a (very good) signal!

- lighter dishes are less likely to damage the mountings/wall/roof, and will cause less strain on any motor used. This may be an important consideration if the size of the dish is approaching the maximum supported by a particular motor (especially for DiSEqC motors)

- some dishes are matched to particular LNBs. The Sky elliptical dishes don't just have any old LNB on them. The internal construction of the LNB is matched to the geometry of the dish. If you were to put any old LNB on such a dish you could expect less gain. See here: http://www.satcure.co.uk/tech/lnb.htm

- A Cassegrain dish looks much like a Gregorian dish inasmuch as they both employ subreflectors and an outward-looking LNB to pick up the refelection back from the subreflector. However, a Gregorian dish has an elliptical subreflector whereas a Cassegrain has a hyperbolic sub-reflector. The elliptical form can be made smaller, so there is less obscuration of the incoming signals. And an offset Gregorian offers the least possible obscuration - hence is the most efficient of all dishes.

- the dish is usually supplied with an arm for the LNB/LNBF, and they can vary in construction. Beware of cheap constructions that may wear/shake loose and cause the LNB to move out of the focal point of the dish - that would more than negate any gain from using a solid rather than mesh dish (for example).

- when all said and done, ask yourself if you NEED the extra gain. After all, a clear digital picture received via a 60cm dish does not get any clearer on a 1m dish (or even a 5m dish...). That is the nature of digital - it is "all or nothing". You would only ever notice the difference when specifically seeking out weak signals or else in severe weather conditions.

More info needed?
Check this out too: http://www.geocities.com/TheTropics/1975/glosarium.html

2old
 

s*t*a*r*m*a*n

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#7
Could bird droppings on the actual dish itself as opposed to the Lmb cause any signal deppreciation or is it negligable?
 

rolfw

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#8
There'd have to be a lot of them, but yes, they could affect the reflected signal. Mind you, with escaping vultures just one would do it :). It's normally more of a problem with prime focus dishes, as the dish angle is shallower and the dirt adheres more readily.

Rolf