Dish alignment and cabling

bubbles

Ello,

I'm moving up to the attic and I need a couple of things.

First of all I need to get my sky dish, which is mounted on my chimley realigned, every since that real windyday about 3 months ago my signal strenght and quality bar have shot down - and the picture breaking up.

Secondly I'm moving up to the attic and I need the dish wired to the attic. At the moment its just coming down the wall, and in via the air vent into my room. I need to get this wired into the attic, which is about 10ft from the dish.

I was on to sky a few months ago and they advised me that I was better off getting a local person to do it.

So, anyone recommend someone? Or is there someone here who has the equipment and abilty who is willing to earn a few extra eurons?

I'm in the Clondalkin area

Thanks.

Greenman

Why don't you try it yourself!!!!.
Look here http://www.davesull.dabsol.co.uk/
Regards JD!!!

TinMan

I used Dunnes Celbridge to do something similar recently and they were very good and quite cheap. You will find them in the phone book 01 area.

Darby OGill

D.I.Y. (IF you have a head for heights and secure ladder and a healthy attitude to personal safety).

I set up my system (i.e. mounting dish, installing cable and tuning in) in about two hours. It's not difficult and the link mentioned above gives excellent advice.

I am now the satellite installation expert in my area- not much cash received yet though...... :rolleyes:

No way would I pay anyone to do something so simple, but maybe I'm just a miserable b*****d.

Good luck.

bubbles

I'm not spending ages trying to point the dish in the right direction when I don't have a clue, tools or ladder.

Will be looking to get this done Tuesday or Wednesday next week.

watty

I you can see the screen you can be lucky on dish re-alignment.
But on a Chimney it is tricky to have the screen.
In any case a Satellite IF signal strength meter is £20stg and really needed, unless you want to spend a long time on the roof.

So finding someone nearby who is either a professional or a properly equiped DIYer is best

Tony

Originally posted by Darby O'Gill
No way would I pay anyone to do something so simple, but maybe I'm just a miserable b*****d.

Good luck.

I'm glad not everyone shares your view, if its that simple nobody would need a proffessional installer. (i exclude skys contractors from this)

Tony

chernobyl

Aligning a dish is a job best left to the professionals..personally i was never any good at it, and i have more man hours than most installers.

You call a pro out, and assuming hes not a cowboy, then this dish is aligned in 15 minutes (anymore and he upping the clock..but this is usually flat fee) and the cables are installed neat and tidy.

Dr. Nick

I re-alligned mine (with the help of m five-y-o who was looking in the window at the screen) last night. It CAN be frustrating, but it's not actually difficult, just a bit of patience required. Once it locks onto the signal, you're laughing.

Greenman

I agree with you Dr Nick.I've been messing with satellite 10 years and have always done things myself or having the wife looking through the window at the TV or sometimes I brought reciever and portable TV outside.
I get great satifaction knowing I've built up the system myself.
Anyway if you did get a pro out here in Belgium you'd pay an arm and leg.DIY is big overhere.
Regards JD!!! Belgium

Darby OGill

I accept that some people will never tackle a job like this, just as I know grown men who are unable to change a bulb. But my experience (and I would consider myself a reasonably good DIYer) is that this is one of the easiest things I have ever done.

But I'm not afraid of heights......

I think everyone knows that many of the "professionals" in every trade like to make simple things seem a bit mysterious, why else would we pay them? I've paid people to do things which they did excellently, others I've had to do it myself afterwards anyway.

Darby

Greenman

Here here,Darby.

JD!!! belgium

Tony

A spectrum analyser costs 1500 euro, no mystery there.I agree with you though some people are professional in name only.

Tony

Originally posted by Darby O'Gill

I think everyone knows that many of the "professionals" in every trade like to make simple things seem a bit mysterious, why else would we pay them? I've paid people to do things which they did excellently, others I've had to do it myself afterwards anyway.

Darby

chernobyl

Originally posted by Darby O'Gill
is that this is one of the easiest things I have ever done.

I am going to give my previous post some context.
Firstly, Bubbles not only wants a dish aligned he wants a cable installed porfessionaly, i attacked my home once with a drill and was instructed that if i ever did so again, i would be homeless.

Secondly, aligining a dish for Nuclear orbital positions like 28.2/19.2 and 13E is pi$$ easy and i can do it without any point of reference [aside from what time it is..and any sunshine].

You guys who claim its easy to align a dish, then try nail 16E, 5E, 1W and 21W and then tell me its simple...

watty

I contomplated moving one of my dishes to Chimney. I've been there changing TV aerial etc. Having it on the Chimney makes it a serious job.

I have 4 Dishes, 2 with 3 LNBs each. I started off lining up dish for BBC OBs in 1977.

The other day I took a Dish down remounted a pole, put dish back and it was picking up Sky before I did anything.... 15miutes of minor adjustments later it was perfect. (With a cheap £20 stg meter and looking at screen).

I had disturbed the pole / dish beside it... That took 2 hrs to fix (3 LNB on that Dish).

You gonna talk on CB or Mobile phone etc and get someone else to watch screen when you on the Chimney? No it needs someone used to Chimneys with a Meter.

Actually the BIGGER the dish the more accurate you have to pint to get anything. the 1m Dish is a PIG, which is why I added an angled pole as a simple "polar" mount. It took AGES to align with help of Telecom2 (Best signal near due south) and 19E (Best analog to east, by nearly 30 degrees, I'm at 11W so a satellite at 11W would be dish at top of "arc"). It only moves by hand, but at least I don't have to readjust up/down.

Most Sky installed dishes are not optimally aligned and they have a £250 meter as apposed to my £20 cheapie, so while it is ABSOLUTELY totally feasible for DIY, I wouldn't dissuade anyone from seeking professional help.

Tony

Originally posted by watty
I'm at 11W so a satellite at 11W would be dish at top of "arc").

Are u sure its 11, seems very far west?

Tony

Dun

Originally posted by Tony
Are u sure its 11, seems very far west?

Tony

The most westerly point is Tearaght Island, which lies in the Atlantic Ocean 12.5 km west of Dingle Peninsula, county Kerry. It lies at longitude 10.70ºW. Of mainland Ireland, the most westerly point is Garraun Point, Dingle Peninsula, county Kerry which is 2.5 km northwest of Slea Head. It lies at longitude 10.51ºW.

Maybe he owns a houseboat

chernobyl

I always thought true south would be the top of the arc?



This "top of the arc" is more prime focus lark anyways.

Tony

Originally posted by chernobyl
I always thought true south would be the top of the arc?

This "top of the arc" is more prime focus lark anyways.

True south (as opposed to magnetic) is top of the arc but the satellite u focus on depends on where you are in the world. Makes no difference whether its prime focus or offset (offset is actually half of a prime focus) if I undertsand u correctly.

Are we off topic yet

watty

Rougly 11 deg.

You can look at OS map or Internet and find where Limerick City is. I can see Limerick City when I look east.

Don't confuse compass bearing for 180 degree, Due South and Degrees East or West.

True Due south is only at 0 Degrees along the Greewich Meridian.

Thor / Intelsat satellite at 1W is only almost due south just abit west of London any place along North South Line.

ALL Dishes have a Prime Focus. That is the optimal place for the LNB. A second LNB on a bracket is not on the Prime focus.
There are lots of kinds of dishes. The common Kind is an Offset Axis Paraboloid, the Prime Focus is not on the centre axis of rotation, but offset, imagine a bigger symetrical dish and you cut a section out of the side and use it. The "Shadow" of the LNB thus falls on the cut away part mostly. The actual refecting part is not shadowed. This is good for less than 1m Dish.

What some people erronously call a "Prime focus" is a symetrical Parabolid where the Prime Focus is along the centre of "rotation " of the Dish. The LNB creates a "shadow" on the centre of the dish. For a small 60cm dish it is a problem. For a 1m dish it is a tiny loss, less than loss of having an Offset design.

No matter what kind of dish you have, no matter where you are, as you track the Satellites 22,500 miles away on the equatorial plane, the Dish will point highest into the Sky when pointing to true Due South (Which is only 0 Degress Satellite position along Grenwich meridian).

Without a polar mount, In Ireland, as you rotate a Dish from 42E(Turksat?) through 28E (Sky) 19E (Astra) 10E (EutelSat) the dish must tilt back, point more upward. At Hispasat (30W) you are well past the apex. The peak is equal to your East/West degrees Around 7 to 11 in western half of Ireland.

The polar mount is simply having the axis of rotation point true Due North South at same angle to ground as a pole at the "north pole", so at equator it is horizontalat north pole it is 90 degrees. Angle depends on distance north.

The Dish is NOT pointing at this angle as it points at a point 22,500 miles away on the equatorial plane. A Equator the difference is Zero. Here it is about 5 degrees different.

If you "sight along" the pole idealy angled to rotate Dish on, you'll see the Pole Star!

chernobyl

Originally posted by watty
ALL Dishes have a Prime Focus. That is the optimal place for the LNB.

I would certainly dispute and i think you can argue (at length) for both.
The biggest dish i ever had was a 1.8Offset and it hammered my neighbours 2.0 prime focus but maybe thats because im just great..dunno

You know your stuff so i dont need to list pros/cons but personally i prefer offset as you can have more fun with them.

Originally posted by watty
No matter what kind of dish you have, no matter where you are, as you track the Satellites 22,500 miles away on the equatorial plane, the Dish will point highest into the Sky when pointing to true Due South

This goes back to my original post when i said "evelvation is more prime focus lark".

A Prime focus dish has one state: The LNb is centre firing and thats it.
You said that any dish as it tracks the sats towards true south will tilt back, while this is completely true it is not necessarily the only option.

I could mount my offset dish completely vertical, aim it for 1W and by adjusting the offset of the LNb arm, still recieve that bird.

That is what makes these dish's much cooler from my perspective.

watty

1) On a Center feed dish, what "chernobyl" erronously calls a Prime focus it is obvious where the LNB ought to go.

If fact if the Arm / tripod is missing, you can measure diameter and depth and calculate the position of the "Prime focus"

As you move the LNB higher or lower, the laws of reflection mean you still get a focus, but you are looking lower or higher in the Sky (inverted Image). As you do this the gain is lower.

2) On an Offset feed dish, it is obvious where the LNB ought to go, ONLY if the arm is correcly mounted.

If fact if the Arm / tripod is missing, THERE IS NO WAY to calculate the position of the "Prime focus"

As you move the LNB higher or lower, the laws of reflection mean you still get a focus, but you are looking lower or higher in the Sky (inverted Image). As you do this the gain is lower. The point of highest gain is the Prime focus.

So which is better?
An offset feed is more expensive to design and make properly than a centre feed. On a small dish and offset feed is better.
As the dish gets larger the advantage of an offset dish is less. While perhaps even a 2m Dish might be offset feed, this is more expensive and little advantgage over center feed. The TYPICAL crossover size between offset feed and center feed is 90cm.

Should I tilt the Dish or the Arm?
On an offset dish there may be an adjustment to tilt the arm. For each model of LNB mounting bracket there is only ONE correct position. The arm should NEVER be tilted except maybe as a fine adjustment. Moving away from the prime focus reduces the gain.

The correct method is always to adjust dish elevation on ALL types of dish.

Why does my dish look like it is pointing horizontal?
If it is offset feed, imagine a laser mounted at the LNB and reflecting off. For Sky it is actually pointing upward at about 24degrees. Remember ALL normal offset feed dishes are part of the top curve of a much bigger "virtual" CENTER feed dish. That is why although you can move the LNB up and down, this is wrong.... An offset dish is *REALLY* a little part of a much biger Center Feed dish.

Why would I deliberately *NOT* use the prime focus on my offset dish?
Just as you can get a satellite by tilting the arm up and down instead of tilting the dish (Which is wrong, as it reduces gain), you can get a satellite by moving LNB to right or left instead of rotating dish Left /right. We use this property that a Dish (OFFSET or CENTER FEED) has only one PRIME FOCUS, but an infinite number of non-prime focii. As you move LNB left further, the gain reduces and "sharpness" reduces, but you "see" a satellite more to the right.

This is why an Offset Dish (or center feed) ligned up with LNB at the Prime Focus for 19E (Astra) can "see" 13E Hotbird with a 2nd LNB mounted to right and very slightly down, and also "see" 28.2E Sky with a 3rd LNB much farther to left (looking at face of dish from LNB) and noticably higher (as satellite "appears" to be lower in sky). The two extra LNBs are thus NOT at the prime focus. The lowest gain is on the SKy LNB, but since Hotbird and Astra need 90cm dish here and Sky signal is high so that a small 65cm dish works, even with this lower gain you get more signal than on a minidish.

I have been a professional Computer and Communications Engineer for nearly 25 years. All the time I see things that may "seem" to work, but are much less than optimal because the theory is missing.

The biggest dish i ever had was a 1.8Offset and it hammered my neighbours 2.0 prime focus but maybe thats because im just great..dunno

This is such an erronous statement. I presume the neigbour's dish is a center feed. Both dishs BY DEFINITION have only a single main or best focus point... called the Prime Focus.

Dishes vary hugely in quality. Similar size dishes can vary hugely in gain, and of course not every dish is equally well aligned, especialy by some of Sky's less expert installers!

Did you know also that the LNB often has metal rings or plastic parts or shape of horn that limits (or focuses) the angle or "cone" of "vision" of the LNB? A special Sky Minidish LNB for UK smaller minidish has such a set of metal rings. Mounted on a 2m dish (offset OR center feed) it will "only see" about 60 or 70cm dish size.

LNB and Dish manufacturers are unwilling to talk about such issues.

If the f/d ratio of a small dish and a big dish are the same, then the LNB will be much father from the dish on the big dish than the "prime focus" on the small dish (even if both are offset feeds), and the "Sky" LNB may be OK.
My 1m dish has the LNB as close as many 65 cm dishes to the dish, so a Sky LNB is no good on it. A really old 1db noise figure LNB gives 4dB better s/n on Thor than the LNB off a UK minidish!


I think it is sad so few schools let all the students do Physics and Chemistry "practicals". A few weeks messing with pins, slit light sources and mirror / lenses gives one such a intuitive understanding about Satellite Dishes.


So I'm not saying offset feed is better or worse than center feed. All I'm saying is that the SAME principles apply to both. They are different designs. There are a three more common designs, but you'll only see them on Cable Head End systems or very large dishes.

ALL designs of dish have only one optimal place for the LNB the Prime Focus. There is NO type of dish called a "prime focus Dish".

bubbles

Jesus lads, I just wanted a contact of someone good to do the cable and allign the dish - thats all!!! So, does anyone know someone?

Tony

Sorry Bubbles we got carried away. Send me an email and i'll try and help.

Tony

chernobyl

Originally posted by watty
1) On a Center feed dish, what "chernobyl" erronously calls a Prime focus it is obvious where the LNB ought to go.

I obviously do not understand what a "Prime Focus" dish is.
It has always been my understanding that a prime focus dish is more "curved" than an offset dish, and has a higher inclination when mounted as it points towards the satellite.
..so what i call "prime" is a centre feed.(mental correction made..hmm)

Originally posted by watty
This is such an erronous statement. I presume the neigbour's dish is a center feed. Both dishs BY DEFINITION have only a single main or best focus point... called the Prime Focus..

I dont know, your quite welcome to survey both dishs although i live in Dublin now..so its a bit difficult to organise.

Originally posted by watty
Did you know also that the LNB often has metal rings or plastic parts or shape of horn that limits (or focuses) the angle or "cone" of "vision" of the LNB? A special Sky Minidish LNB for UK smaller minidish has such a set of metal rings. Mounted on a 2m dish (offset OR center feed) it will "only see" about 60 or 70cm dish size.

This was a point i made only last week (i was wrong then too).
It is important to distinguish between LNb and LNbf...although i cannot imagine anyone cellotaping a Sky LNb to their shiny 2.0M dish..

LNB and Dish manufacturers are unwilling to talk about such issues.

For the most part the LNbf and dish pair is a "non issue".
Most people are aiming for a bird and are also located within the hot spot of the satellite beam, so filtering noise for useable signal is not really an issue.

oh yeah..and you spelt erroneous wrong..nanana

Tony

Originally posted by watty
1) . There is NO type of dish called a "prime focus Dish".

Well of course there is, I have one in my back garden, perhaps Prime focus type dish is a better way to describe it but talk to anyone in the industry and they will recognise what a prime focus dish is as opposed to an offset type dish.

Tony

watty

Sorry Bubbles... about the lecture. If Iwas closer I'd sort it.


Tony..
Because SO MANY people have called a Center Feed dish a "Prime Focus" dish, of course delaers know what you mean. Also many dealers are good at running a business. They are not qualified Communications Engineer.

Look at top 1/3 of a centre feed dish. That is the offset dish. That is why the inclination of an offset dish "looks" less than an centre feed dish. For the same satellite, at the same place, the actual Inclination for all types of dish is the same. The apparent inclination is different. Excluding a Mini Dish I have 4 different offset dishes (3 in use). They all would sit at slightly different apparent angles because they are all different phyiscal parts of different "virtual" center feed dish.

All center feed dishs pointing at the same place will of course look as if pointing higher (but arn't or it wouldn't "see" the Satellite).

If you mount an Offset dish upside down it would be nearly flat (and fill with water or snow) (to point at same place) as it would then be effectively the bottom portion of a large "virtual" center feed dish.

Check the books (and Uni sites with google). Or Ask Martin Pickering www.satcure.com (Though he gets more sarcastic than me).


Actually I *HAVE* got a LNB for UK sky minidish tied on the arm of a 90cm offset dish. I gave away my minidish to a caravan owner and was adding a second Digibox. The 90cm dish was free as it had no arm. I fitted one by "trial and error" as only with Center feed you can calulate "prime focus". It isn't very good for hotbird, but fine for a digibox. My "good" 90cm offset dishes each have 3 LNBs each.

(A quad LNB would be nearly £70stg, to feed PC and two Digiboxes. I got some single LNBs for £7 each)

Tony

Originally posted by watty
Sorry Bubbles... about the lecture. If Iwas closer I'd sort it.


Tony..
Because SO MANY people have called a Center Feed dish a "Prime Focus" dish, of course delaers know what you mean.

Not only dealers but manufacturers. When I went to seminars with astra they even called them that. We seem to be going round in circles here discussing interpretation of terms so perhaps we should leave it be now:cool:

Tony

watty

I'll try and be less pedantic
and Shorter!
Urlan TV are fairly expert in the Limerick / Clare area (though I havn't used them). I'm sure there must be decent & reasonable Installers in Bubbles area.

jmcc

Originally posted by watty

2) On an Offset feed dish, it is obvious where the LNB ought to go, ONLY if the arm is correcly mounted.

If fact if the Arm / tripod is missing, THERE IS NO WAY to calculate the position of the "Prime focus"

It is difficult but it is not impossible. The simplest method would be to ring the distributor and get the dimensions.

The proper term is 'prime focus parabolic dish' but as with any commonly used term, it get shortened in use. Therefore people end up calling it 'prime focus'.

On the 1.8M offset versus 2.0 dish, I've seen such variations. The early Trac dishes were well designed and used to give very good results. However the spun aluminium dishes that were common around the same time used to flatten in transit. The other factor on this was that the scalar feed horn used on many of the cheap knock-off polarotors was not that well engineered and did not illuminate the dish properly. Going back even further, a copy of a scalar feedhorn that was in circulation here prior to polarotors did have an impedance matching problem.

ALL designs of dish have only one optimal place for the LNB the Prime Focus.

All designs of parabolic dishes. It is easy to fall into the trap of truncating terms. Even the polar mount is actually a modified polar mount as it has to incorporate a declination angle to tilt the dish forward so that it would hit the arc.

Aligning a modified polar mount when there is a satellite at or very near the True South position is actually very easy though it does require two other satellites at the extremes of the arc as markers. (I think I wrote it down somewhere. If anyone wants it, I can post it. ) It should take only a few minutes to do it but if you follow the bullsh1te methods in some textbooks you would be there all day.

Regards...jmcc

watty

Yes, I used Telecom 5W for near top and Sky 28.3E and Hispasat 30W to align. I used the original elevation adjuster on my dish to do the "declination" adjsustment.
Basically I cut a piece of pole long enough to mounthe the Dish mount on.
I mounted that pole on the top of a pole using a second old pole /dish mount to allow the short length of pole to be tilted around 50 degrees and rotated to point true North (not magnetic north).

I mounted dish on it and ensured the Dish mount would rotate on pole and tilt on pole. A Satellite at 8W is too Weak so I used 5W to roughly setup top of arc.

The idea is that when you swing it round in the dish mount (The mount with angled pole is NEVER rotated once it points true nortH), you do not have to retilt the dish.
You can use any kind of dish, except a minidish is a bit small for most satellites and more than a 1M dish is going to need serious concrete, poosibly guy wires and very stong pole. Offset or Center feed is irrelevant.

There is a sequence to adjusting to get it smooth pointing at correct arc.

Next I'll add a wiper motor and an old 286 PC to control position by joystick port (put Joystick connected sensor to sense Wiper motor angle, use 2nd joystick "volume control" to set position)