Question LNB skew problems

gualo

Novice Member
LNB skew problems

Location: Evesham, West midlands (35 miles south of Birmingham)

Equipment used so far: -

Receiver: Echolink EL-888 FTA Super+ (purchased solely to set up the dishes but not DVB-s2 Compliant... D'oh)
Dish: megasat 80cm offset aluminum
LNB: inverto Black Premium Selected Quattro 40mm LNB
Distribution gear: Spaun SMS 91809NF multiswitch
Coax: WF100 shotgun


Hello everyone, This is my first foray into the world of satellite TV and it has been a steep learning curve so if I have made any howling errors... be kind - and when you've finished laughing any help will be really appreciated!

Below is a photo of the story so far: -

DSCF3965.JPG

NB. The photo is taken looking quite steeply upwards so the scaffolding handrail does not actually pass in front of the larger dish. (It is below it)

Preamble: -

The small 60cm dish on the right is aligned with hotbird and my lodger uses it to receive all her Polish channels.

My plan is to replace this dish with two 80cm dishes (one aimed at hotbird 13E and the other at astra2 28E) then distribute the feeds around the house using the multiswitch

As this is my first attempt at messing around with satellite dishes of any sort I thought I would take it one step at a time and so my first step has been to align the dish on the left with hotbird and compare results with the existing smaller dish before moving on to fitting the other one...


The first results I got seemed promising as typical signal levels and signal quality from the 80cm dish seem better than the small one.

I felt a little disappointed about the actual numbers (80cm dish in the west midlands should surely give some pretty high readings) however having read around it seems as though the actual numbers on any given receiver are largely arbitrary and the main point is I saw an improvement. So ready for the next stage then... Or so I thought


Here's where I need some help: -

Before taking down the old dish I did a final comparison only this time I used my lodgers polish receiver to check the HD channels and discovered when tweaking the LNB skew I am getting conflicting sweet-spots from different channels/transponders. Is this normal?

Signal strength is showing 95-99% on everything so I am disregarding that and looking at the quality indications.

TVN HD (TP 11508V) can be tweaked to an indicated 76%ish SQ but...
POLSAT (TP 12264V) then falls to 38%ish

Conversely if I skew the LNB a couple of degrees to favor POLSAT (I then get a rise from 38% to 66%ish) TVN HD then drops to the low 40's.

I realize that without professional Sat meters all these figures are arbitrary and will differ according to varying atmospheric conditions but...

It is as if these two vertically aligned transponders are not in the same plane.

I have currently set the Skew to halfway between the two sweet-spots making a compromise and I await some heavy rain to find out if this is good enough!

Can anyone tell me if this is normal or is it an indication something else might be off?

I have tried a number of things already but there is a danger this post is about to challenge Tolstoy's "war and peace" on the word count so if I have missed out any key information please don't flame me just yet!

Any help or ideas will be greatly appreciated!
 

logiciel

Moderator
Hi and welcome to Satellite.
My only comment is that 28 and 13 should be very easy to get with one smaller dish.
 
Last edited:

TJT1

Member
With two LNBs mounted on the same dish. Why have two when you can have one?
 

pedro2000uk

Distinguished Member
LNB skew problems

Here's where I need some help: -

Before taking down the old dish I did a final comparison only this time I used my lodgers polish receiver to check the HD channels and discovered when tweaking the LNB skew I am getting conflicting sweet-spots from different channels/transponders. Is this normal?

Signal strength is showing 95-99% on everything so I am disregarding that and looking at the quality indications.

TVN HD (TP 11508V) can be tweaked to an indicated 76%ish SQ but...
POLSAT (TP 12264V) then falls to 38%ish

Conversely if I skew the LNB a couple of degrees to favor POLSAT (I then get a rise from 38% to 66%ish) TVN HD then drops to the low 40's.

I realize that without professional Sat meters all these figures are arbitrary and will differ according to varying atmospheric conditions but...

It is as if these two vertically aligned transponders are not in the same plane.

I have currently set the Skew to halfway between the two sweet-spots making a compromise and I await some heavy rain to find out if this is good enough!

Can anyone tell me if this is normal or is it an indication something else might be off?

I have tried a number of things already but there is a danger this post is about to challenge Tolstoy's "war and peace" on the word count so if I have missed out any key information please don't flame me just yet!

Any help or ideas will be greatly appreciated!

might be interference or overload & going 'off' skew reduces overload/ bleed over or the effect of interference, over one - you can push a motorised off best position deliberately to bring about a similar end result.
 

gualo

Novice Member
Hi everyone, thanks for the prompt replies.

My only comment is that 28 and 13 should be very easy to get with one smaller dish.

My thinking for using an 80cm dish was I am using a quattro LNB and distributing to 18 feeds. muxing terrestrial, FM, Dab and CCTV onto the down-leads and re-splitting them all at the faceplates.

DSCF3968.JPG


DSCF3969.JPG

Or at least - I will be!

I (maybe wrongly) assumed that there was a potential for this arrangement to be "more lossy" than a 50-60cm dish with outputs direct to a receiver.

With two LNBs mounted on the same dish. Why have two when you can have one?

I thought two dishes might be less troublesome (particularly in terms of setup and signal loss, especially considering the distribution system) than two offset LNB's - Is my ignorance already so apparent ;)

Hi Pedro, I understand the idea that going "off skew" could help in terms of reducing too much gain but is that consistent with the two vertical transponders requiring a different skew angle in order to be "off skew"?

Finally I was hoping for plenty of "rain headroom" (The little dish is prone to failing in certain poor atmospheric conditions) and I hadn't realized an 80cm dish might be so much overkill.

Is there any way of attenuating the signal from the bigger dish in "fine" conditions whilst retaining "rain headroom"?

Thanks again all.
 

logiciel

Moderator
On second thoughts you'd probably be best with them both on the one 80cm dish.
 

pedro2000uk

Distinguished Member
Hi everyone, thanks for the prompt replies.



...
Hi Pedro, I understand the idea that going "off skew" could help in terms of reducing too much gain but is that consistent with the two vertical transponders requiring a different skew angle in order to be "off skew"?

...

you do get things like that - more obvious on C band, had a customer alter an lnb settings & improved one [which had plenty of margin] and lost others

I'd do the same and get the best average if another answer can't be found - trying other lnbs would be one thing


with multi-switches- the rule is, keep it much cleaner & up the input signal a dish size or two but not so you are overloading the system.

multi lnbs on a dish add noise & drop signal as soon as you put an lnb off the focal point - they work only to a degree and ideally you avoid adding noise into multi-switches & IRSs
 

gualo

Novice Member
Thanks for the further replies.

I'd do the same and get the best average if another answer can't be found - trying other lnbs would be one thing

Hi Pedro -when you say try other LNB's This is the one currently in use

Inverto - IDLB-QUTL40-PREMU-OPP -

I have another identical one (intended for the other dish) - should I try that or do you mean a different make etc?

with multi-switches- the rule is, keep it much cleaner & up the input signal a dish size or two but not so you are overloading the system.

It sounds as though I should stick with the 80cm dish then. and that is consistent with some of the professional installations such as this one I have seen in the same town.
DSCF4045.JPG


You mentioned interference - is there any way I could find out more about the likelihood (or possible preventative measures)

Thanks all.
 

pedro2000uk

Distinguished Member
try a different make lnb

the dish or quattro chosen on that IRS doesn't necessarily say professional
 

gualo

Novice Member
Hi Pedro - and thanks for your time.

the lnb I mentioned: -
Inverto - IDLB-QUTL40-PREMU-OPP -
is listed as part of their proline range so I was wondering what you meant?

I can see from your other posts you are a respected professional so I was wondering if you might suggest any LNB/Dish combinations that will improve things.

Thanks.
 

pedro2000uk

Distinguished Member
you could use any lnb - maybe even a quad if the Spaun can switch a quad -just to test it for that but Inverto are one of the most respected consumer LNB manufacturers, so I'd still use those & average it out.

It's easy to make a dish as cheap as possible & look the same as any other, a cheap, soft steel or [soft] ali' face can be cheaply pressed but will also distort easily, a poor azel will not grip as well & can bend & there's the quality of rust treatment on steel parts versus painting un-prepped steel.

I worked on a prime example of one someone had bought a few days ago- I just wanted to swap it for a Triax. Triax = higher tensile steel face with a % of spring steel characteristics that takes strong winds & retains it's shape, zinc phosphate treated steel then positively charged x powder coated that stays rust free for well pushing 15-20 years. An AZEL that probably has the best AZ pole grip & EL lock in the business.
 

gualo

Novice Member
Hi Pedro,

I have just tried (gently) distorting the dish with my hand whilst looking at the signal and it very rapidly degrades (The dish is a Megasat Aluminum).

When mounting the dish to the backplate I made sure the metal tabs placed no distortion forces on the parabola and as you can see from my first post I have mounted it in a position to minimize wind loading . (It helps having a south facing wall)... But you've got me wondering!

I am now thinking it might be worth trying a triax. Do they have different quality options or is a triax - a triax? I have found an anthracite TP78 for £32.95 (am I allowed to say where from on a forum?) but they don't seem to stock it in terracotta can you get hold of them?

Regards
 
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pedro2000uk

Distinguished Member
I've never tested that dish so can't say, pure aluminium is very malleable but alloys of it can be incredible. Triax td 50 64 78 88 dish faces do flex quite a bit on their own, but that changes when bolted to Triax's long, curved flanged AZEL. You can't tell too much off a picture of a dish face- a shallow angled rim is usually not a good sign, the AZEL & feed arm design can be a good indicator.

Make sure the face is true.

You can paint satellite dishes, the general rules are to keep it thin & even with a silk finish & don't use metallic.
 

gualo

Novice Member
I have now found a triax TD78, TDS78 and TDA78 with the S & A standing for Steel and Aluminum which I guess would explain why some suppliers describe the TD as a steel dish and others describe it as an aluminum dish.

Which one would you recommend?

Terracotta or Brick red triax's seem to be popular in Germany but besides finding some on amazon for over £100 each I have had no luck - so my thoughts turn to painting...

I can see from trawling the forums that the subject of paint comes up regularly and the (sensible) advice seems to be: -
  • Keep it thin and even... therefore spray rather than brush.
  • Avoid metallics/metal flake because of the possibility of increasing interference and signal noise.
  • Avoid high gloss because of increased light and heat transmission to the LNB
  • Avoid matt because it encourages the build up of other deposits and it takes longer to shed snow and water.
That narrows things down a bit!:facepalm:

Do you know what sort of (silk or mid sheen) paint is likely to adhere long term to the factory polyester finish of a triax dish?

Flaking DIY painted plastic car bumpers come to mind - yuk:thumbsdow
 

pedro2000uk

Distinguished Member
..
Do you know what sort of (silk or mid sheen) paint is likely to adhere long term to the factory polyester finish of a triax dish?

Flaking DIY painted plastic car bumpers come to mind - yuk:thumbsdow

You are very thorough & ask all the right questions. The dish you have might be OK though,

The same basic rules of painting apply, dry, free from grease & dust, key the surface, thin, even coat/s & make sure the base won't react etc..
 

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