Request for advice: dish wobbling in the wind, alignment & signal quality


Peter Novak
 

Dear group,
we have installed a 120cm satellite dish on a roof of an office building
at a relatively exposed location near the sea coast in the Netherlands.
Things work quite fine, in good weather conditions our signal strength
is at -25/-26dBm and Es/No at 13.0-13.5dB with solid link margins for
both BAS (~7.4dB), as well as HVS (~3.6dB). We are receiving HVS stream
data. That's all fine and well. However, in more windy conditions the
dish wobbles quite a lot (easily by 2-4cm at the top), which in turn
leads to misalignments, occasional loss of lock and subsequent loss of
received files. As an example, I made a short video of the dish moving
in 6 Bft wind here: https://owncloud.hq.meandair.com/s/Zo3mKIsiRk9ByG5

I wonder what solutions other group members are using to mitigate this
problem. I looked at some metal support arms/struts which would affix
the dish sides to the mast better than now, but I don't even know how
are such products called.

I would appreciate any advice, or pointers to improvements of the setup
to mitigate the misalignments in windy conditions we are experiencing.

Thanks a lot for your advice.

Best regards,

Peter.


Barry Smith
 

In message <20210505081740.GS8018@meandair.com>
"Peter Novak" <eumetcast@newsite.meandair.com> wrote:

Dear group,
we have installed a 120cm satellite dish on a roof of an office building
at a relatively exposed location near the sea coast in the Netherlands.
Things work quite fine, in good weather conditions our signal strength
is at -25/-26dBm and Es/No at 13.0-13.5dB with solid link margins for
both BAS (~7.4dB), as well as HVS (~3.6dB). We are receiving HVS stream
data. That's all fine and well. However, in more windy conditions the
dish wobbles quite a lot (easily by 2-4cm at the top), which in turn
leads to misalignments, occasional loss of lock and subsequent loss of
received files. As an example, I made a short video of the dish moving
in 6 Bft wind here: https://owncloud.hq.meandair.com/s/Zo3mKIsiRk9ByG5
I wonder what solutions other group members are using to mitigate this
problem. I looked at some metal support arms/struts which would affix
the dish sides to the mast better than now, but I don't even know how
are such products called.
I would appreciate any advice, or pointers to improvements of the setup
to mitigate the misalignments in windy conditions we are experiencing.
Thanks a lot for your advice.
Best regards,
Peter.
I haven't experienced problems like this. My 1m dish is in a sheltered
location.

What you could try is "guy wires" one end attached to the dish rim
(top, left and right?) the other end attached to the concrete slabs.

I have used https://www.radioworld.co.uk/radioworks-kevlar-guy-rope/ke
vlar-super-strong-guy-rope---50m-spool
on my vertical amateur radio aerial with duplex 3mm rope clamps like
these https://www.ebay.co.uk/itm/363341019743
You could use eye bolts in the concrete slabs and dish rim something
like these https://www.ebay.co.uk/itm/232025047765

Barry
--


Ernst Lobsiger
 

On Wed, May 5, 2021 at 01:17 AM, Peter Novak wrote:
I would appreciate any advice, or pointers to improvements of the setup
to mitigate the misalignments in windy conditions we are experiencing.
Hello Peter

I looked up the mechanical specs of your SAB Satellite (S120/M120) dish here:

https://www.sabsatellite.nl/upload/files/1452181362-SAB%202014%20dishes.pdf

It's 108.2 x 120.6cm in 0.9mm steel. Mast diameter possible 34 - 60mm.

Already the mast diameter span is close to unacceptable for a 120cm dish.
Also the long pillar for the LNB does not look very stable for a 120cm dish.

Your problem seems to be a resonance effect with the natural mechanical
oscillation frequency of the dish. The steel material works like a spring with little
attenuation and the frequency is low because the M120 mount is not wide enough.

A couple of us use a Gibertini OP 125 L. You find the specs under this link:

https://www.gibertini.it/index.php/en/antennas-uk/op-125-l

Compare: We use the 1.5mm aluminum dish. Mast diameter span is 55 - 100mm.
6 Bft is 40 - 50km/h. I have never seen wobbling with much stronger winds.

I attach two images of my dish. Please note the stable construction of the LNB support.
But also note the mass of concrete plates used to keep my homebrew tripod struts on
the ground. YOUR CONSTRUCTION LOOKS TOO LIGHTWEIGHT FOR A 120cm DISH!

You most probably will not find any commertial cure for a consumer product like this.
This means you have to homebrew your own solution. You will need a minimum
of mechanical tools and skills and get some material from a harware store.

Here is my advice:

1) Make sure your antenna is not blown away. Use another 4 concrete plates.

2) Try to stabilize the dish with 4 aluminum stripe struts to the pole.
   The downside is this makes repointing close to mission impossible.
   Also it's possible that the dish can be distorted by temperature effects.
3) As an alternatve you can try to introduce some mechanical attenuation.
   This could be some thick plastic tube, corrugated electric pipe, garden
   hose or even of these  https://www.flickr.com/photos/rvoegtli/4650067041
   "Fun Noodles" that you clamp H/V accross on the backside of your dish.
4) You can bring down the natural oscillation frequency by attaching left
   and right a 1kg screw clamp to the brim (on your own risk and peril!).

5) Buy a more professional dish and a solid/heavy 80mm mast construction.


Good Luck

Ernst


Youssef Bennouna
 

Peter,
It's an important issue for most amateurs as they generally put their
satellite dishes on top of the roof. The wind patterns on the roof are not
the same as an open field, in some places, the winds are stronger and weaker
in others. The wind strength, gusts, and turbulence vary from place to place
on the roof. It depends on many factors like the height of the building, the
existence and height of neighboring buildings, the direction of the dominant
wind...local winds are not the same as those measured by a weather station.
A better assessment of local conditions is necessary before choosing the
right location for the dish, taking into account of course other factors
like cable distance, clear view of the satellite etc.
Here are some pictures showing wind distribution patterns around and over
buildings (from CFD study, comments are in French). This might help you
figure out a better place for your dish and avoid very installing heavy
mechanical duty to stabilize it.
I hope this will help.
Best regards


Youssef Bennouna
ETUDES ET MESURES LES 5 DOMAINES

Villa 176, Bassatine El Menzeh
12123 - EL MENZEH
MAROC
TEL : (+212) 0537 01 14 41
GSM : (+212) 0661 10 97 43

-----Message d'origine-----
De : MSG-1@groups.io [mailto:MSG-1@groups.io] De la part de Peter Novak
Envoyé : mercredi 5 mai 2021 08:18
À : MSG-1@groups.io
Objet : [MSG-1] Request for advice: dish wobbling in the wind, alignment &
signal quality

Dear group,
we have installed a 120cm satellite dish on a roof of an office building at
a relatively exposed location near the sea coast in the Netherlands.
Things work quite fine, in good weather conditions our signal strength is at
-25/-26dBm and Es/No at 13.0-13.5dB with solid link margins for both BAS
(~7.4dB), as well as HVS (~3.6dB). We are receiving HVS stream data. That's
all fine and well. However, in more windy conditions the dish wobbles quite
a lot (easily by 2-4cm at the top), which in turn leads to misalignments,
occasional loss of lock and subsequent loss of received files. As an
example, I made a short video of the dish moving in 6 Bft wind here:
https://owncloud.hq.meandair.com/s/Zo3mKIsiRk9ByG5

I wonder what solutions other group members are using to mitigate this
problem. I looked at some metal support arms/struts which would affix the
dish sides to the mast better than now, but I don't even know how are such
products called.

I would appreciate any advice, or pointers to improvements of the setup to
mitigate the misalignments in windy conditions we are experiencing.

Thanks a lot for your advice.

Best regards,

Peter.


Peter Novak
 

Hello Ernst, group,
thanks a for your response. It's indeed very useful and informative.

I looked up the mechanical specs of your SAB Satellite (S120/M120) dish here:

https://www.sabsatellite.nl/upload/files/1452181362-SAB%202014%20dishes.pdf

It's 108.2 x 120.6cm in 0.9mm steel. Mast diameter possible 34 - 60mm.

Already the mast diameter span is close to unacceptable for a 120cm dish.
It's 42mm diameter, 2mm steel. From your comment I understand a thicker
one would be better. That is indeed an option.

In fact, we originally designed the setup for a 96cm dish, but that
turned out to produce too weak signal, so we replaced it later on
without changing the mast, hence the diameter.

Also the long pillar for the LNB does not look very stable for a 120cm dish.
Stabilisation of the arm seems like a good idea too.

Your problem seems to be a resonance effect with the natural
mechanical oscillation frequency of the dish. The steel material works
like a spring with little attenuation and the frequency is low because
the M120 mount is not wide enough.
Thanks. That makes sense indeed. Regarding the not enough wide mount you
mean the mast diameter, or generally construction of the dish mount at
the back of it?

I attach two images of my dish. Please note the stable construction of
the LNB support. But also note the mass of concrete plates used to
keep my homebrew tripod struts on the ground. YOUR CONSTRUCTION LOOKS
TOO LIGHTWEIGHT FOR A 120cm DISH!
Those are 2 layers of 4 concrete tiles, each 22.5kg heavy. That makes
180kg anchor weight on the flat roof stand construction. Do you think
it's not enough? I mean, another layer of tiles would make +90kg, that's
easy to do, but will it help?

2) Try to stabilize the dish with 4 aluminum stripe struts to the pole.
The downside is this makes repointing close to mission impossible.
Also it's possible that the dish can be distorted by temperature effects.
We had something like that in mind indeed. It seems this is indeed the
factor which would help most.

4) You can bring down the natural oscillation frequency by attaching left
and right a 1kg screw clamp to the brim (on your own risk and peril!).
As a quick fix that might be a good idea too. From your comments, I also
understand that I need to speak to a mechanical engineer for advice - I
am a software guy :-).

5) Buy a more professional dish and a solid/heavy 80mm mast construction.
That's indeed what I understand from your comment above. Just to
understand it clearly. It seems you think that large part of the problem
is actually the mast bending like a spring and the dish contributes only
in part. Is that correct?

Actually, another idea could be to weld a tripod structure between the
mast top and the stand below similarly as you have it on the high pole
you have there.

Also, I checked out the Gibertini dish you mentioned, but I see it's
also steel material of 1mm thickness, while the one we use is 0.9mm.
Does it make a difference? Apart from a better connected arm, could you
please explain how is that Gibertini dish actually significantly better
than the one we have? As I said, I am not a mechanical engineer, so I am
learning along the way here. To my layman eyes, these are bent metal
plates one like the other :-).

Thanks a lot for your help, I really appreciate.

Best,

Peter.


Peter Novak
 

Thanks Youssef for your response. Those images from simulations make
sense indeed. Unfortunately, for now, repositioning at our site is not
really an option, we are limited by a high rise building to the
south-east from our place. But yes, one thing we are looking at is to
move the whole setup to a different location completely. By now it's
clear that closer to the ground could be actually safer than the 5th
floor we are.

Thanks again for your help.

Best,

Peter.

On Wed, May 05, 2021 at 02:48:48PM -0000, Youssef Bennouna wrote:

Peter,
It's an important issue for most amateurs as they generally put their
satellite dishes on top of the roof. The wind patterns on the roof are not
the same as an open field, in some places, the winds are stronger and weaker
in others. The wind strength, gusts, and turbulence vary from place to place
on the roof. It depends on many factors like the height of the building, the
existence and height of neighboring buildings, the direction of the dominant
wind...local winds are not the same as those measured by a weather station.
A better assessment of local conditions is necessary before choosing the
right location for the dish, taking into account of course other factors
like cable distance, clear view of the satellite etc.
Here are some pictures showing wind distribution patterns around and over
buildings (from CFD study, comments are in French). This might help you
figure out a better place for your dish and avoid very installing heavy
mechanical duty to stabilize it.
I hope this will help.
Best regards


Youssef Bennouna
ETUDES ET MESURES LES 5 DOMAINES


Ernst Lobsiger
 

On Wed, May 5, 2021 at 09:57 AM, Peter Novak wrote:
That's indeed what I understand from your comment above. Just to
understand it clearly. It seems you think that large part of the problem
is actually the mast bending like a spring and the dish contributes only
in part. Is that correct?
Peter,

I didn't see the second layer of your concrete plates. In any case you should
expect forces of >=500 N (>= 50 kp) in 120 km/h gusts on the mast clamps. At
some place of the video it even looks as if the plates are lifted (may not be real).

From the video it's rather hard to see how much is twisting of the mast tube and
how much is actually bending of the SAB steel dish itself. The Gibertini OP 125L
is sold as 1mm steel dish but also as 1.5mm aluminum dish. Aluminum is rather
ductile and cannot work as a spring. My idea of introducing some attenuation
to the "eigenfrequency" assumed that the bending of the dish is essential.

Youssef has a good point as well. The video starts with showing a vertial
edge of a huge red and close building. This can produce heavy turbulence.
But as you said moving the dish somewhere to a calm place is not possible.

It's certainly a good idea to let a mechanical engineer or physicist have a look.

Regards,
Ernst


J.W. Davies
 

I agree with Ernst that there is significant wind resonance effects
there. The dish is clearly too flimsy for the windy location.

However, a few things you may wish to try:-

I notice the feed arm has significant movement and this is probably the
source of the biggest impact on signal strength. The position of the LNB
at the focus is very critical.

There is an old trick from the days of Band 1 television where the
hollow aerial elements had a length of rope inserted during manufacture
to dampen wind resonance.
It looks like the LNB feed arm is hollow. So you could try inserting a
piece of rope, tightly fitting in the length of the arm to dampen it.

I agree with the comments of others that the mast is rather weak.
Its not clear how much that is moving from the video but that could also
be packed with pieces of ropes to stiffen and dampen.
If it is blocked at the bottom then even filling it with sand may help.

The flimsy reflector is more problematic. If needed after trying the
above, one possibility is to strengthen the back by applying fibreglass
matting and resin to build up the thickness. The surface being “keyed”
by roughing it with carborundum/ sand  paper first.

The possibility of shielding the back and sides with wooden/plastic
panelling, as a windbreak,  say about 1.5 Metres high, may be another
possibility. The panelling should not be a solid wall as you will get
turbulence downwind, making the situation worse. The panelling should
have gaps in it to make it permeable to the wind, slowing the wind
rather than  stopping it.

Whether its worth the effort is another question and getting a stronger
dish such as the Gibertini OP 125 L may be less hassle.

Regards
James

On 05/05/21 09:17, Peter Novak wrote:
Dear group,
we have installed a 120cm satellite dish on a roof of an office building
at a relatively exposed location near the sea coast in the Netherlands.
Things work quite fine, in good weather conditions our signal strength
is at -25/-26dBm and Es/No at 13.0-13.5dB with solid link margins for
both BAS (~7.4dB), as well as HVS (~3.6dB). We are receiving HVS stream
data. That's all fine and well. However, in more windy conditions the
dish wobbles quite a lot (easily by 2-4cm at the top), which in turn
leads to misalignments, occasional loss of lock and subsequent loss of
received files. As an example, I made a short video of the dish moving
in 6 Bft wind here: https://owncloud.hq.meandair.com/s/Zo3mKIsiRk9ByG5

I wonder what solutions other group members are using to mitigate this
problem. I looked at some metal support arms/struts which would affix
the dish sides to the mast better than now, but I don't even know how
are such products called.

I would appreciate any advice, or pointers to improvements of the setup
to mitigate the misalignments in windy conditions we are experiencing.

Thanks a lot for your advice.

Best regards,

Peter.







Peter Novak
 

Thanks James. Your ideas are also very useful. I found a
mechanical engineer in my close network I will ask him to translate your
and Ernst's ideas into a concrete advice at our site.

I appreciate your help.

Best,

Peter.

On Wed, May 05, 2021 at 09:26:29PM +0100, J.W. Davies wrote:

I agree with Ernst that there is significant wind resonance effects
there. The dish is clearly too flimsy for the windy location.

However, a few things you may wish to try:-

I notice the feed arm has significant movement and this is probably the
source of the biggest impact on signal strength. The position of the LNB
at the focus is very critical.

There is an old trick from the days of Band 1 television where the
hollow aerial elements had a length of rope inserted during manufacture
to dampen wind resonance.
It looks like the LNB feed arm is hollow. So you could try inserting a
piece of rope, tightly fitting in the length of the arm to dampen it.

I agree with the comments of others that the mast is rather weak.
Its not clear how much that is moving from the video but that could also
be packed with pieces of ropes to stiffen and dampen.
If it is blocked at the bottom then even filling it with sand may help.

The flimsy reflector is more problematic. If needed after trying the
above, one possibility is to strengthen the back by applying fibreglass
matting and resin to build up the thickness. The surface being “keyed”
by roughing it with carborundum/ sand  paper first.

The possibility of shielding the back and sides with wooden/plastic
panelling, as a windbreak,  say about 1.5 Metres high, may be another
possibility. The panelling should not be a solid wall as you will get
turbulence downwind, making the situation worse. The panelling should
have gaps in it to make it permeable to the wind, slowing the wind
rather than  stopping it.

Whether its worth the effort is another question and getting a stronger
dish such as the Gibertini OP 125 L may be less hassle.

Regards
James


J.W. Davies
 

Please let us know how you eventually solve your problem.

Your real life experience may be of use to others in a similar situation.


Regards

James

On 06/05/21 08:38, Peter Novak wrote:
Thanks James. Your ideas are also very useful. I found a
mechanical engineer in my close network I will ask him to translate your
and Ernst's ideas into a concrete advice at our site.

I appreciate your help.

Best,

Peter.

On Wed, May 05, 2021 at 09:26:29PM +0100, J.W. Davies wrote:

I agree with Ernst that there is significant wind resonance effects
there. The dish is clearly too flimsy for the windy location.

However, a few things you may wish to try:-

I notice the feed arm has significant movement and this is probably the
source of the biggest impact on signal strength. The position of the LNB
at the focus is very critical.

There is an old trick from the days of Band 1 television where the
hollow aerial elements had a length of rope inserted during manufacture
to dampen wind resonance.
It looks like the LNB feed arm is hollow. So you could try inserting a
piece of rope, tightly fitting in the length of the arm to dampen it.

I agree with the comments of others that the mast is rather weak.
Its not clear how much that is moving from the video but that could also
be packed with pieces of ropes to stiffen and dampen.
If it is blocked at the bottom then even filling it with sand may help.

The flimsy reflector is more problematic. If needed after trying the
above, one possibility is to strengthen the back by applying fibreglass
matting and resin to build up the thickness. The surface being “keyed”
by roughing it with carborundum/ sand  paper first.

The possibility of shielding the back and sides with wooden/plastic
panelling, as a windbreak,  say about 1.5 Metres high, may be another
possibility. The panelling should not be a solid wall as you will get
turbulence downwind, making the situation worse. The panelling should
have gaps in it to make it permeable to the wind, slowing the wind
rather than  stopping it.

Whether its worth the effort is another question and getting a stronger
dish such as the Gibertini OP 125 L may be less hassle.

Regards
James