Trying to reach Astra 2D from 63 latitude Sweden

lloowen

Hello all and merry Christmas.

I live in mid Sweden and I am trying to reach the Astra 2d satellite.

Perhaps I should give some information about my hardware. The satellite dish is 1.8m and is 45cm deep. From what I can see the tripod mount that holds the lnb is a bit of a home made job! The dish it's self has been lying around for quite some time and I had to replace the lnb.
Based on the formula below, it looks like the tripod is set at the right focal length, which is (50cm):

(diameter x diameter)
------------------------------ = focal length (50cm)
(16 x depth of dish)

The lnb I used is a 0.2db, I figured this would do as

(50cm focal length)
------------------------- =0.28
180cm diameter


I am using a digital satellite meter (Horizon HDSM USB) to find the Astra 2d satellite. When I do a sweep, I get a strong signal on

h Astra 2d lo 28E tp51 dbu
v Astra 2d lo 28E tp52 dbu
I am getting 99%-100% signal strength on these, however when I try and get

h Astra 2d lo 28E and v Astra 2d lo 28E I can't get a lock!

Please have a look at the attached photo. The focal length sits just behind the face of the old lnb in this photo. The same is with the new lnb. Does the focal length have to be right at the front of the lnb? Also if you look at the photo you will notice the angle of the lnb is not 90degrees to the dish. Should it be angled at 90degrees to the dish?

Grateful for any help. I can't figure out why I get a really strong signal on the transponders, but I can't pick up any channels.

thanks
lloowen

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Channel Hopper

Is it a prime focus or offset dish ?

There is a very fine line between "hobby" and "mental illness"

lloowen

It is a prime focus dish.

pedro2000uk

If it's a prime focus the LNB has to be 90 degrees and with both types... it's aim has to be to the centre of the dish. After you have modified the feed support arms so they hold the lnb level (if it's a prime focus), stand behind the lnb or the holder without the lnb in place and eye the aim of the LNB down its body through the feed horn or holder... we use a laser in place of the LNB that fits the holders.

You will need to fine tune the focal length not just rely on the calculation ...

...and you also need to match the F/D ratio for that dish... an LNBf will be completely wrong for a prime focus dish.. too shallow and cut a large area of the dish off. A C120 flanged lnb and an adjustable c120 flanged feed horn is probably your best bet to illuminate the whole dish if it's a prime focus.

The calculations for focal length & f/d ratio are not the same if it is an offset..

BTW... I would fine tune that dish on another satellite (23.5e?) or stronger beam on 28e first before attempting 2D.

lloowen

Thanks for the advice. When you mean a prime focus dish, you mean a dish that is perfectly round with a curve that is the same all the way round the dish.

lloowen

Please could you recommend any of these if any will do. I have translated the site using google translate.

_http://translate.google.com/translate?hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.satpro.se%2Fdefault.asp%3Fid% 3D10401&sl=sv&tl=en&history_state0=

Very grateful for the help.

pedro2000uk

yes... and the LNB is held in the middle... usually by three arms but there are other designs.

lloowen

Now I have altered the angle of the lnb so that it is now 90 degrees to the dish. I managed to get a lock onto the Astra 2d satellite, though the best I can get is 11% signal quality. A lot of fiddling about with the distance and skew of the lnb to the dish. I actually managed to get a number of channels with quite a good reception, though the reception is not consistent, as the lnb is not sitting firmly in place. I had to take one of the legs of the tripod mount away so that I could align the holder to sit 90 degrees to the dish!

Looks like I'm going to have to get one of those if I want to increase the signal strength. I can foresee a problem in how I set one of these up on the dish.
I mean the distances and angles have to be perfect. Any tips n tricks on how to set up a tripod mount for the lnb on the dish?

I can see that would be very useful for alignment, but how do align the tripod mount so that the holder is perpendicular to the dish? How does one decide where to drill holes in the dish for the tripod mount? The spacings for the tripod mount on my dish are a bit suspect and don't look symetrical in relation to the distances between each leg and to the center point of the dish. A total home made bodge job!

Also with my dish, I assumed the focal length was 50cm, but I notice that the signal strength increased when I pushed the lnb nearer to the dish, though this would mean the lnb is not sitting at the focal point of the dish. The focal point would be at the neck of the lnb instead! So if the focal point is 50cm for my dish. Where should the lnb be in realation to the focal point? Just in front of the lnb, on the face of the lnb, just behind the lnb?

thanks again,

lloowen

pedro2000uk

Sounds like excellent progress lloowen!

Could you upload a photo that shows the whole dish face and those arms?

Sounds like you should start again with those support arms... before you do that you must establish it's best position focal length wise and work from there.

Where the focal point is exactly on an LNBf is one of life's mysteries... it's about 40mm in from the face and then allow for fine adjustment.

To aim the LNB holder to the middle of the dish is easy.. just look down it and sight it in line... a small length of 40mm plastic waste tube in the holder is helpful..

The main thing is the F/D ratio once you have the focal length OK and remade those arms ... with an LNBf (most with an f/d ratio of .6) on a dish with a 50cm focal length that is about the same as some 60-70cm dishes and that's all it might see.

If you don't mind trashing a cheapo LNBf (5 euro etc..) as an experiment (before buying an adjustable feed horn and C120 LNB)... you could try sawing the feed horn right off one... that plate that holds the LNB will help act as a bit of a scala ring and you can make a better one later...(and seal the lnb sawn off front)

EDIT ... I would do all this on an easier satellite or beam first.

lloowen

Here's some photos. Any comments?

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pedro2000uk

Nice pictures...(we love pictures)...

If you calculated the focal length as 500mm then you should gain a mile if you can get that LNB in another 30mm or so by that tape... except the .6 f/d feed horn will chop a bit more off round the edge too the nearer it gets until you cut it off...

That looks like it might be about right for a C120+ feed horn though so I wouldn't modify it too much without considering being able to fit both LNBfs & C120s/ feed horns.