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Optimizing signal

ckrys1

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#1
I have been trying to check the alignment of my 1.2m prime focus dish with polar mount and actuator.
It seems to me there are 3 things that can be `tweaked`, and I would be interested to know in which order to do them.
1. LNB position
2. Dish elevation - am I right in saying this is altered by moving a large, almost vertical, pole up and down. An arm from this pole is attached to the back of the dish and there is a nut on either side of the connection, so presumably I loosen the nuts and move the pole up and down?
3. Dish offset angle - is this the smaller sliding nut which is marked on a scale of 1-10, and mine is set to about 6? (I live in East Scotland).

My problem is if I set the lnb to its best position, and then change the offset angle, do I then go back to the lnb which may not now be in the best position. And if I change the elevation angle, does that mean the offset angle should be tweaked again?

Grateful for any help - if anyone can recommend a book on Motorised installation I`d also be very interested

Ckrys1
 

rolfw

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#2
Hi Ckrys1,

Obviously as a start your dish mounting pole should be vertically plumb.

The elevation can be adjusted by slightly loosening the pivot and adjustment bolts on the back of the dish and moving up or down, not the pole height. The satellite is many thosand miles away and so a small adjustment in height will make no difference, it must be in the vertical angle of the dish face.

The best way of achieving optimum position is to stand below or behind the dish and grip the dish on both sides, then gently tilt in one direction (bolts still tightly fastened), if the signal on the receiver rises then move the dish slightly in that direction. Keep doing this until there are no mor signal rises with either side to side (azimuth) or up and down (elevation) movements.

Once you have got the best from that exercise you can then experiment with the LNB skew (rotation) you can find out exact figures from http://www.smw.se/smwlink/smwlink3.zip for ready calculator

http://www.heavens-above.com/countries.asp this page will get your exact coordinates

If your LNB can be moved back and forth, you may need to play with it to get the optimum focal length.

Rolf
 

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#3
Quite a few dealers with shops will sell you an inexpensive meter (runs inline with the signal cable) for about £20 - in the UK that is
The better the signal the higher the pitch of the tone generated, so it can be used for doing both dish alignment as well as the LNB focal position

You will save probably an hour or two in the cold simply by listening to the sound from the meter than running back and forwards to the TV

Then you can keep the meter inline to ensure that the motor returns the dish to the same spot and for peaking those moving satellites
 

wolsty

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#4
I've been fiddling with my alignment over the last few months and have done a fair bit of reading up on it. However, I am still puzzled by the difference between signal quality and signal strength. Can anyone explain, please? Does CH's meter measure strength or quality?

wolsty
 

rolfw

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#5
[updated:LAST EDITED ON 15-Nov-01 AT 08:47 PM (GMT)]The audible meter will only measure strength, but with a perfect alignment will normally follow good quality, providing the cable run is good, the skew is right and there are no obstructions.

I would back up CH on the effectivity and speed of the audible meter, many a time I've had to revert to one when the more sophisicated gear is broken or more commonly has run out of juice. :) The tilt and move method works particularly well with this type of meter.


Rolf

PS. The main difference between strength and quality is that you can have high strength and low quality and get picture break up, but you can have low strength and high quality and get perfect picture performance. The quality aspect is the performance of transmitted signal against carrier noise, the lower the noise the better.

I'm sure Channel Hopper or 2old could put it better though :)
 

wolsty

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#6
That's pretty good! I understand the strength bit now. However is quality just a subjective issue, or is there a way to measure it?

wolsty
 

rolfw

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#7
[updated:LAST EDITED ON 15-Nov-01 AT 10:21 PM (GMT)]Yes Wolsty, it's measured in either signal to noise ratio, or bit error rate. The meter that the Sky installers use measures in bit error rate, but expressed as a quality reading 0 being worst and 99 being best. Some digital receivers express it as noise I believe, so that the scale is reversed.

Rolf
 

2old4this

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#8
ckrys1
there are actually three independent variables in aligning a motorised dish
(a) inclination
(:cool: declination
(c) alignment to south

(c) is obvious.
But (a) and (:cool: are sometimes confused.

Inclination is the angle between horizontal and the mount's axis of rotation.
Declination is the angle between the mount's axis of rotation and the plane of the dish.

If any one of those three are not precisely set, then you will at best get only part of the whole arc of satellites.

2old
 

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#9
Dear 2Old

You forgot

4) True polarmounts - some setups - particularly on offset dishes - do not allow full tracking of the geostationary arc down to the horizon. A lot of fiddling and some filing may be required to ensure you get the lower elevation satellites (which quite often are also weaker)

5) The offset angle - or skew - of the incoming signal. Nowadays it is highly likely the system used will have a Universal LNB with no manual polarisation adjustment - save for the final lockdown into the clamp at the front of the dish. Satellites near the centre of the arc (exception is Telecom 5West) will run 0 and 90 degree polarisation quite well but others away from the highest point will need to have the LNBtwisted slightly to improve one or the other polarisation

And of course there are the satellites that move a bit away from the geostationary arc, Europestar B, Intelsat 31.5W, but thats another story.

Signal quality is simply the maximum signal when compared to the background noise of the rest of the system set up. Minimising noise wherever it comes in to your equipment by any means will help the situation, a larger dish correctly set up has by far the best improvement in one step, replacing of anything else (with the exception of maybe wrongly fitted line amps or cable connectors) will not have as dramatic impact. You could end up replacing almost everything if you find a channel off one satellite is not behaving.
 

ckrys1

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#10
Really helpful comments - I think I`m getting there, but 2 further questions.
1. I have fiddled with the declination of my dish quite successfully, improving signal on all sats, but I have not been able to alter the inclination, mainly `cos I`m not sure which bolts to slacken! - and I`m a bit tentative lest the whole thing collapses! However, am I right in saying that one should set the inclination first by looking for the best signal on 1W, as it`s nearest true south, and only then fiddle with the declination and optimise the signal on a couple of sats either side, and if you`ve done that, all the other sats should `fall into place` (except for the fact that a few are in inclined orbit)?

2. And this may really sound a daft question, but I`ve stared at this dish for hours working out how to alter the inclination - my wife`s becoming jealous of it! Do I have to disconnect the actuator from either the back of the dish or the polar mount, or both, before I can alter the inclination?

Thanks again

Ckrys1
 

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#11
Inclination will normally be a set of two nuts on a long threaded bar either at the front or the back of the dish (usually running more or less parallel to the post)

Setting this is best done when the dish is positioned on a satellite near true South and is adjusted in conjunction with the declination bolts (usually directly behind the dish itself).

There is also the North/South (or azimuth) and all three work together in aligning the movement to the geo arc, however if you are already getting satellites East and West then this should not need any major fiddling
 

ckrys1

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Yep, I know the `long threaded bar`, but when I loosen these nuts and try to alter the inclination, the dish doesn`t move - so should I loosen the actuator bolts on the back of the dish? or are their other bits I have to loosen? or Am I just not pushing/pulling the dish hard enough?

Ckrys1
 

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#13
There will be a large bolt that runs through the main canister that holds everything onto the post. This is horizontal and is usually a 17 / 19 or 22 mm nut and lock washer

Loosen this ever so slightly and then you will be able move the dish up and down