MSG-1 Dish alignment and wind


Robert Moore
 

I have real problems because my dish is mounted in the only place on my house
where I can see MSG-1. I am going to fix a mild steel rod from the mounting
pole to the wall some way from the bracket so that I have a strong triangle.
Today I have tried to damp the oscillation of the dish on the pole by placing a
light rubber rope around the bottom of the dish and the bracket, there is
hardly any tension on this but I hope it will stop pole and dish oscillating in
sync and thus amplifying small movements. I'll have to see - when the wind
blows.
My unavoidable dish-exposure is slightly compensated for by the fact that I am
exposed from west through north to east, whereas the prevailing winds are from
the south west - even a SW gale leaves my garden calm, though the clouds race
overhead.
SO I'm hoping that with some damping and far fewer NW winds I will not suffer
too much loss over the year. Those of us with similar problems can keep one
another posted through the list.
Robert.

Quoting Arne van Belle <a.van.belle@hccnet.nl>:

David wrote:
Interestingly, during wind and rain, when I have missed segments,
the indicators have not dropped anything like that low, suggesting
perhaps that the indicators average over too long a period to show
problems, and that momentary drops due to wind (moving the dish) may
be quite important.

My findings:
The Signal Quality readout is a 1-second average value that does not detect
short signal drops.
As the name implies it does not show signal level but the quality of the
received signal !
When I put an additional line-amplifier in, the readout remains the same
and during a solar outage the readout dropped where as my Satellite signal
meter showed and increase.

I did some calculations based on receiving Hotbird with an 88 cm dish.
This dish has a "half power" beam-width of only 2 degrees at 11096 MHz. So
if the dish moves in windy conditions, a deflection of 1 degree left and 1
degree right (same applies for up and down movement) could already cause a
loss of half of the signal (-3dB)

When the left rim is pushed back 7mm (and the right rim comes forward 7mm)
you have a 1degree misalignment!
If your mounting brackets are not that stiff (like the one from Robert
Moore) they could bend too much in the wind.
As Robert discovered the dish will start to oscillate and the signal drops
and rises too fast to be detected on the Signal Quality readout.
I have not tried this but I guess you can detect the signal drops using a
Satellite signal meter because this does not average.

But now an interesting case: Suppose the dish is already 0.5 degree
misaligned, normally this will only give a small signal reduction but now
you only have an allowable deflection of 3.5 mm in one direction ! That
really requires a very stiff dish mounting !

I welded a wall mounting myself because I was not satisfied with the
commercially available mounts, they are too long and the bolts fixing the
mounting to the wall are placed very close to each other.
I placed the dish as close to the wall as possible to keep the mount as
short as possible.
Take a look at the file I uploaded to the Files area.
80cmMSGdish.jpg (288 kb)

So if you suffer from missing segments at high winds, watch for movement of
the dish..
Don't mount the dish on a high or unprotected spot if there is no need.
Have the dish re-aligned with a Satellite signal meter because
wind-movement will aggravate any error.
If necessary add additional bracing(s) to a fixed point to prevent the dish
from oscillating in high winds.

Compared to receiving Meteosat 7 on 1691 MHz we need a more accurate
alignment and a stiffer mount.
There is not much difference between receiving digital TV satellites and
MSG over DVB, but every short "freeze" on a TV satellite set will result in
a lost segment on MSG !

Greetings,
Arne van Belle



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------------------------------
Professor Robert Moore
Department of Sociology, Social Policy
and Social Work Studies
The University of Liverpool
Eleanor Rathbone Building
Bedford Street South
Liverpool
L69 7ZA

tel and fax: 44 (0) 1352 714456


Hugh Marnoch
 

The extra rod will give you much more rigidity and should cure any problem you have with dish movement 'if' the pole is moving in the wind enough to lose the signal. One of the satellite dish makers used to do a fitting just like that using a 60cm length of right angled steel with a simple bent plate bracket for the wall end, one hole for the wall bolt and one for a coupling nut and bolt. The other end of the rod bolted on to the dish end of the mounting arm, simple but very effective.

Hugh.

*********** REPLY SEPARATOR ***********

On 12/10/2003 at 17:55 Robert Moore wrote:

I have real problems because my dish is mounted in the only place on my
house
where I can see MSG-1. I am going to fix a mild steel rod from the mounting
pole to the wall some way from the bracket so that I have a strong
triangle.
Today I have tried to damp the oscillation of the dish on the pole by
placing a
light rubber rope around the bottom of the dish and the bracket, there is
hardly any tension on this but I hope it will stop pole and dish
oscillating in
sync and thus amplifying small movements. I'll have to see - when the wind
blows.
My unavoidable dish-exposure is slightly compensated for by the fact that
I am
exposed from west through north to east, whereas the prevailing winds are
from
the south west - even a SW gale leaves my garden calm, though the clouds
race
overhead.
SO I'm hoping that with some damping and far fewer NW winds I will not
suffer
too much loss over the year. Those of us with similar problems can keep one
another posted through the list.
Robert.

Quoting Arne van Belle <a.van.belle@hccnet.nl>:

David wrote:
Interestingly, during wind and rain, when I have missed segments,
the indicators have not dropped anything like that low, suggesting
perhaps that the indicators average over too long a period to show
problems, and that momentary drops due to wind (moving the dish) may
be quite important.

My findings:
The Signal Quality readout is a 1-second average value that does not
detect
short signal drops.
As the name implies it does not show signal level but the quality of the
received signal !
When I put an additional line-amplifier in, the readout remains the same
and during a solar outage the readout dropped where as my Satellite
signal
meter showed and increase.

I did some calculations based on receiving Hotbird with an 88 cm dish.
This dish has a "half power" beam-width of only 2 degrees at 11096 MHz.
So
if the dish moves in windy conditions, a deflection of 1 degree left and
1
degree right (same applies for up and down movement) could already cause
a
loss of half of the signal (-3dB)

When the left rim is pushed back 7mm (and the right rim comes forward
7mm)
you have a 1degree misalignment!
If your mounting brackets are not that stiff (like the one from Robert
Moore) they could bend too much in the wind.
As Robert discovered the dish will start to oscillate and the signal
drops
and rises too fast to be detected on the Signal Quality readout.
I have not tried this but I guess you can detect the signal drops using
a
Satellite signal meter because this does not average.

But now an interesting case: Suppose the dish is already 0.5 degree
misaligned, normally this will only give a small signal reduction but
now
you only have an allowable deflection of 3.5 mm in one direction ! That
really requires a very stiff dish mounting !

I welded a wall mounting myself because I was not satisfied with the
commercially available mounts, they are too long and the bolts fixing
the
mounting to the wall are placed very close to each other.
I placed the dish as close to the wall as possible to keep the mount as
short as possible.
Take a look at the file I uploaded to the Files area.
80cmMSGdish.jpg (288 kb)

So if you suffer from missing segments at high winds, watch for movement
of
the dish..
Don't mount the dish on a high or unprotected spot if there is no need.
Have the dish re-aligned with a Satellite signal meter because
wind-movement will aggravate any error.
If necessary add additional bracing(s) to a fixed point to prevent the
dish
from oscillating in high winds.

Compared to receiving Meteosat 7 on 1691 MHz we need a more accurate
alignment and a stiffer mount.
There is not much difference between receiving digital TV satellites and
MSG over DVB, but every short "freeze" on a TV satellite set will result
in
a lost segment on MSG !

Greetings,
Arne van Belle



To unsubscribe from this group, send an email to:
MSG-1-unsubscribe@yahoogroups.com



Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/





------------------------------
Professor Robert Moore
Department of Sociology, Social Policy
and Social Work Studies
The University of Liverpool
Eleanor Rathbone Building
Bedford Street South
Liverpool
L69 7ZA

tel and fax: 44 (0) 1352 714456


To unsubscribe from this group, send an email to:
MSG-1-unsubscribe@yahoogroups.com



Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/


a_van_belle
 

Hello Robert and Hugh,

Finding the right spot to mount your dish is not easy.
But with some simple re-inforcements you can stiffen the existing
mount. Placing a rod "triangling" the existing mount will help a lot
and does not put in much weight.
You could also try to use a pre-tensioned steelwire from a fixed
point to the pole just below the dish mounting to dampen.
Don't think that a mesh dish is a solution here. At this high
frequency the mesh should be minimum 2mm and won't be very open when
hit by a gale.
You could try a bit smaller dish, this has less surface and a wider
beamwidth, relaxing a bit on the stiffnes of the mount.

Greetings,
Arne van Belle