PDA

View Full Version : Freeview Dish measurements



Driftwood
05-07-2009, 03:28 PM
I've been searching the net & these pages for some info.
The arm holding the LMD on my dish got blown by the frost.
I have repaired it but need to get it re-aligned corectly on the dish.
I have found specs for my particular dish but don't know to apply them.
For example where exactly is the focal point measured from?
Just how critical is the alignment?
I guess what I am looking for is a picture of a dish, showing where the various angles & measurements apply.
I have posted this on some freeview forums but havent been swamped with help.

tweak'e
05-07-2009, 05:03 PM
i assume you mean LNB arm.
buggered if i know how one would get blown down by frost ;)

but anyway need pic so can get an idea of what dish it is etc. normally if the arm come off you can see where its broken off and simply place the arm back on those marks.

alainment is normally resonable critical but you can normal adjust the LNB to suit. i've seen installers put the arms on inside out, upsidedown and backwould and the dish still works ok.

Driftwood
05-07-2009, 05:15 PM
Thank you for your reply.

Yes sorry, LNB.

The arm filled with rainwater which froze & split the tube, also altering the angle of the bend.

It is a 75cm KU Band Offset Dish Antenna. SK75-PW/G.

As I said, I have the Offset Angle & Focal Length, just need to know how/where to apply them.

Strommer
05-07-2009, 05:22 PM
To align the dish for Freeview:

http://forums.overclockers.co.nz/showthread.php?t=18358

http://www.geekzone.co.nz/forums.asp?ForumId=34&TopicId=15221

http://columbiaisa.googlepages.com/tv_sat_zipcode.htm

Optus D1 (160E) – Freeview, Sky, TVNZ channels, DW, Nasa TV, CCTV9.

Look up the satellite on http://www.lyngsat.com and you can get all the info from there.

Better yet, enter your address here: http://www.satmax.co.nz/support.htm

pine-o-cleen
05-07-2009, 05:32 PM
The arm holding his LNB is bent Steve_L, so none of that is going to help him.

tweak'e
05-07-2009, 07:24 PM
ok i get it. the drain hole in the arm blocked up, filled up with water and froze splitting it. provided you didn't cut the tube you should just be able to bend it back.
if you have focal legth you should be able to measure that off the surface of the dish in several places, where they intersect is roughly where the pickup inside the LNB should be.
if you had a meter you could simply bend back to where ever the signal is the strongest.

otherwise just ask around, there is proberly a few damaged dishes around you could get a new arm off.

Driftwood
05-07-2009, 08:31 PM
There are no spare parts available in this area.
So I either buy a new disk or repair this one.
I can bend this arm to any position, but what I need to know, bearing in mind this is an offset disc.
1/ Does the angle through the centre of the LNB intersect at the centre of the dish?
2/ Is the focal length, the distance from the white face of the LND to the centre of the disc?
3/ What exactly does the offset angle refer to?

Here is a similar dish.

http://www.freetv.co.nz/webapps/site/61418/52840/shopping/shopping-view.html?pid=250599&b_id=&find_groupid=4975

R2x1
05-07-2009, 09:16 PM
You could carefully remove the LNB & replace it with a sausage, spray the dish with oil, rub aluminium foil onto the inside surface, then, aiming the dish at the sun, put the sausage in the hottest bit and when the smoke curls up you will understand why the sausage is the sacrificial target. Don't get your hands near the focal point, or you will find out why you shouldn't have.
Although not as much fun as a sausage, a sheet of paper does not blank out too much sun, and makes it a bit easier to find the focal point.

Driftwood
05-07-2009, 09:50 PM
I wouldn't mind seeing the sun. It would be a nice change. We had snow last week & prior to that 3 weeks of sub zero temps.

R2x1
05-07-2009, 11:44 PM
Snow and ice are fine on post cards or out plane windows. They should not be released near regular peoples habitats lest the lettuces go a bit weird.

ps: I remember sunshine, my memory must be better than I thought. (Or my forgettory is failing.)

Driftwood
06-07-2009, 09:49 AM
Thats great but can you help with my problem.

R2x1
06-07-2009, 10:48 AM
Well, if yours is the same brand and diameter (SVEC, 750mm) as mine, I could give you the measurements from my dish.

seltsam
06-07-2009, 01:06 PM
With a signal meter (Satellite finder - $30 from tricky Dicky) you could use trial and error until the best signal strength is obtained.

Driftwood
06-07-2009, 02:23 PM
I have actually got one of those but it wouldn't tune in properly.
That's when I realised what the problem was.
I have bent the arm back roughly to where I think it was but I would rather get it correct before putting the thing back up on the roof.

tweak'e
06-07-2009, 03:00 PM
i'm a bit rusty but offset angle is generally angle off centre line.
with offset disk focal length from dish varies.

unfortunately you took the whole dish down which makes it harder. if you had just taken the arm off you could have fixed it then bent it into place till the signal was the best.

frankly unless you can find a dish to copy from it may be easier to buy another.
otherwise just get it roughly right and hope you can get it lined up ok with the sat. with a bit of mucking around you should be able to get it in the ballpark.

its disgusting that they call the Satellite finders signal meters :(

Driftwood
06-07-2009, 04:19 PM
I wasn't too worried about loosing the setting by taking it down.
It was never mounted properly in the first place.
Because of the slope of the roof it wasn't possible to mount the base plumb wthout modifying it.
We just bolted it down & lined it up with the meter.
It's worked fine for 18 months until this happened.
I'm going to use this opertunity to modify the base correctly.

Driftwood
06-07-2009, 04:26 PM
Well, if yours is the same brand and diameter (SVEC, 750mm) as mine, I could give you the measurements from my dish.

If it's the same as this one, then it is identical.

http://www.trademe.co.nz/Electronics-photography/TVs/Other/auction-224677907.htm

tweak'e
06-07-2009, 06:04 PM
I wasn't too worried about loosing the setting by taking it down.
It was never mounted properly in the first place.
Because of the slope of the roof it wasn't possible to mount the base plumb wthout modifying it.
We just bolted it down & lined it up with the meter.
It's worked fine for 18 months until this happened.
I'm going to use this opertunity to modify the base correctly.

i wouldn't worry about it. having the mount plumb simply makes it easier to line up to the sat (and it looks neater). much more important to have it mounted securely. I've seen too many houses with badly installed dishes that have damaged the house.

R2x1
06-07-2009, 11:08 PM
If it's the same as this one, then it is identical.

http://www.trademe.co.nz/Electronics-photography/TVs/Other/auction-224677907.htm
Mine is probably even more identical than that - I'll measure 'er up in the morning, weather permitting.

Driftwood
06-07-2009, 11:50 PM
That would be great.
Weather permitting I will be modifying the mount tomorrow.
It's mounted on the side of a valley on a tiled hip roof.

Driftwood
08-07-2009, 10:22 AM
I guess the weather is not the best in North Shore.

R2x1
08-07-2009, 10:25 AM
OK, sorry about yesterday, a Dragon quest used up nearly all the spare daylight, and since I do not wish to experience her Kung Fu, I complied with the directives from the nearest source of menace.
From the rim of the dish at the top, on the formed ridge that is nearest the sattelite to the satellite side of the LNB mounting ring (top edge) is 843 mm. From there to the ground is 2.2 R2's, but it seemed further. (The dish overhangs the roof edge.)

Driftwood
08-07-2009, 01:53 PM
Thanks for doing that & I'm glad there wern't any accidents.
With a bit of luck I'll get this thing back up & tuned in today.
It's still only 3 degrees here.

Driftwood
09-07-2009, 06:17 PM
Well we had some sun today which melted the frost off the roof, so we are back in business.

R2x1
09-07-2009, 06:59 PM
Naturally today was fine and calm here since I did not have any outdoor tasks to catch up on. The Dragon was complaining about the time it takes her to cut the lawns, so I took pity on her and pointed out that if she runs with the mower she could be finished in half the time. As a result of my kind assistance she can now get all the other little jobs done too.
If it wasn't for the distance involved I'ld send her down to rig the dish for you. No point in you risking a fall and harming the garden when she is so small and wouldn't hurt the plants at all. ;)