Hi all,
I cannot remember this question being discussed before!
If you have a nice array of VHF and UHF antennas - 2 stacked X 8 foot long yagis one ach band plus a 2 foot S band dish, is it best from wind loading and other reasons to park it: vertically pointing straight up (the dish has a hole at the bottom) pointing to the horizon towards the prevailing wind somewhere else?
I know that at SSTL in Guildford they are usually parked pointing straight up but I have never been able to find anyone with a really good explanation for doing so.
If you look at 193.51.07.114 you can see the sort of array that I am talking about!
Many thanks
Graham G3VZV
----- Original Message ----- From: "Graham Shirville" [email protected] To: [email protected] Sent: Tuesday, September 02, 2008 6:35 PM Subject: [amsat-bb] How best to park your satellite antennas
Hi all,
I cannot remember this question being discussed before!
If you have a nice array of VHF and UHF antennas - 2 stacked X 8 foot
long yagis one ach band plus a 2 foot S band dish, is it best from wind loading and other reasons to park it:
vertically pointing straight up (the dish has a hole at the bottom) pointing to the horizon towards the prevailing wind somewhere else?
I know that at SSTL in Guildford they are usually parked pointing straight
up but I have never been able to find anyone with a really good explanation for doing so.
If you look at 193.51.07.114 you can see the sort of array that I am
talking about!
Many thanks
Graham G3VZV
Hi Graham, G3VZV
Pointing straight up with the main supporting boom in direction of the dominant wind is the best because the dish will offer the minimum surface to the wind while both yagi's are aligned in a way to be seen by the wind as about a single antenna.
The above is my experience with less damages into the windy gulf of Naples
73" de
i8CVS Domenico
At 09:16 AM 9/2/2008, i8cvs wrote:
----- Original Message ----- From: "Graham Shirville" [email protected] To: [email protected] Sent: Tuesday, September 02, 2008 6:35 PM Subject: [amsat-bb] How best to park your satellite antennas
Hi all,
I cannot remember this question being discussed before!
If you have a nice array of VHF and UHF antennas - 2 stacked X 8 foot
long yagis one ach band plus a 2 foot S band dish, is it best from wind loading and other reasons to park it:
vertically pointing straight up (the dish has a hole at the bottom) pointing to the horizon towards the prevailing wind somewhere else?
I know that at SSTL in Guildford they are usually parked pointing straight
up but I have never been able to find anyone with a really good explanation for doing so.
If you look at 193.51.07.114 you can see the sort of array that I am
talking about!
Many thanks
Graham G3VZV
Hi Graham, G3VZV
Pointing straight up with the main supporting boom in direction of the dominant wind is the best because the dish will offer the minimum surface to the wind while both yagi's are aligned in a way to be seen by the wind as about a single antenna.
The above is my experience with less damages into the windy gulf of Naples
73" de
i8CVS Domenico
Generally, large radio astronomy or space tracking dishes are parked at zenith because this presents the smallest area exposure to winds. Also, the dish load is balanced on its pedestal. For a satellite array the long yagis present as much wind area as a small 2-foot dish. One could point the array directly into the wind but this would present the full area of the dish to wind loading. If the array is pointed 90-degrees from the wind direction and pointed to the zenith, wind area would be minimized.
For my new 16-foot eme dish there is another consideration (living in Alaska). That is snow loading. A dish pointed straight up will fill with snow and rain definitely overloading it. The best stow position is on the horizon and pointed 90-degrees to the prevailing wind. Large dishes should have tie-down wires for further stablization in high winds.
So it varies with the situation and type of antennas. The idea is to minimize wind area.
***************************************************** 73, Ed - KL7UW BP40iq, 6m - 3cm 144-EME: FT-847, mgf-1801, 4x-xp20, 185w http://www.kl7uw.com AK VHF-Up Group NA Rep. for DUBUS: [email protected] *****************************************************
----- Original Message ----- From: "Edward Cole" [email protected] To: "i8cvs" [email protected]; "Graham Shirville" [email protected]; "AMSAT-BB" [email protected] Sent: Wednesday, September 03, 2008 5:42 AM Subject: Re: [amsat-bb] Re: How best to park your satellite antennas
At 09:16 AM 9/2/2008, i8cvs wrote:
----- Original Message ----- From: "Graham Shirville" [email protected] To: [email protected] Sent: Tuesday, September 02, 2008 6:35 PM Subject: [amsat-bb] How best to park your satellite antennas
Hi all,
I cannot remember this question being discussed before!
If you have a nice array of VHF and UHF antennas - 2 stacked X 8 foot long yagis one ach band plus a 2 foot S band dish, is it best from wind loading and other reasons to park it: vertically pointing straight up (the dish has a hole at the bottom) pointing to the horizon towards the prevailing wind somewhere else?
I know that at SSTL in Guildford they are usually parked pointing straight up but I have never been able to find anyone with a really good explanation for doing so.
If you look at 193.51.07.114 you can see the sort of array that I am talking about!
Many thanks
Graham G3VZV
Hi Graham, G3VZV
Pointing straight up with the main supporting boom in direction of the dominant wind is the best because the dish will offer the minimum surface to the wind while both yagi's are aligned in a way to be seen by the wind as about a single antenna.
The above is my experience with less damages into the windy gulf of Naples
73" de
i8CVS Domenico
Generally, large radio astronomy or space tracking dishes are parked at zenith because this presents the smallest area exposure to winds. Also, the dish load is balanced on its pedestal. For a satellite array the long yagis present as much wind area as a small 2-foot dish. One could point the array directly into the wind but this would present the full area of the dish to wind loading. If the array is pointed 90-degrees from the wind direction and pointed to the zenith, wind area would be minimized.
For my new 16-foot eme dish there is another consideration (living in Alaska). That is snow loading. A dish pointed straight up will fill with snow and rain definitely overloading it. The best stow position is on the horizon and pointed 90-degrees to the prevailing wind. Large dishes should have tie-down wires for further stablization in high winds.
So it varies with the situation and type of antennas. The idea is to minimize wind area.
73, Ed - KL7UW
Hi Ed, KL7UW
I am happy that you agree with me so please read the following.
A flat reflector with diameter D = 1.128 meters has a surface S = 1 square meter
At a wind speed of 120 Km/h with the wind perpendicular to it the force applied to the mounting frame is 70 Kg (kilograms)
If the reflector is a deep dish the above force must be multiplied by K=1.6 and it becames 112 Kg / square meters
If a wind at 120 Km/h is applied perpendicular to standard antennas with a net total metallic surface of 1 square meter K= 1.4 and the force applied to the mounting frame becames 98 Kg / square meters
With Passive Reflectors and Antennas with flat radome K=1 and for antennas with aerodynamic Radome K= 0.8
It follow that the force applied to the mounting frame of a deep dish with D = 60 cm when pointed directly into a wind direction at 120/Km/h is about 31 Kg
Consequently pointing straight up with the main supporting boom in direction of the dominant wind as I suggested that is the same that you suggested using different words:
If the array is pointed 90-degrees from the wind direction and pointed to the zenith, wind area would be minimized.
it seems to be the best parking position because the dish will offer the minimum surface to the wind while both yagi's are aligned in a way to be seen by the wind as about a single antenna.
In addition the wind will see the main supporting boom as a single point wich surface is only the small diameter of the pipe.
In the above conditions the torque applied by the wind to the Elevation rotator is the minimum possible and the same for the Azimutal rotator.
Infact if you point the antennas stright up at 90 degrees elevation and 90 degrees from the wind direction if you disconnect the mechanical joint between the azimuthal rotator and the mast you will see that under wind conditions the antenna will search the minimum load against the wind positioning itself as naturally did a flag or as suggested by you Ed and by my self in the above messages.
73" de
i8CVS Domenico
On 2 Sep 2008 at 19:16, i8cvs wrote:
----- Original Message ----- From: "Graham Shirville" [email protected] To: [email protected] Sent: Tuesday, September 02, 2008 6:35 PM Subject: [amsat-bb] How best to park your satellite antennas
Hi all,
I cannot remember this question being discussed before!
If you have a nice array of VHF and UHF antennas - 2 stacked X 8 foot
long yagis one ach band plus a 2 foot S band dish, is it best from wind loading and other reasons to park it:
vertically pointing straight up (the dish has a hole at the bottom) pointing to the horizon towards the prevailing wind somewhere else?
I know that at SSTL in Guildford they are usually parked pointing straight
up but I have never been able to find anyone with a really good explanation for doing so.
If you look at 193.51.07.114 you can see the sort of array that I am
talking about!
Many thanks
Graham G3VZV
Hi Graham, G3VZV
Pointing straight up with the main supporting boom in direction of the dominant wind is the best because the dish will offer the minimum surface to the wind while both yagi's are aligned in a way to be seen by the wind as about a single antenna.
The above is my experience with less damages into the windy gulf of Naples
73" de
i8CVS Domenico
Hi Domenico and Graham
Under your latitude it's probably the best way to park a dish but if you lived at an higher latitude things can be quite different...
Look at the first 3 pictures on my web page www.qsl.net/ve2dwe
You will understand why radome are built for. and a bit pricey for an amateur stand point.
This event happens in December first 2006 one of numerous mother nature bad effect but we don't have hurricane here and no palm trees...
"-"
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
Thanks for all the comments...and apologies for the link error ...it should have read 193.51.107.114
73
Graham
If you look at 193.51.07.114 you can see the sort of array that I am
talking about!
Many thanks
Graham G3VZV _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Looking at the picture, Domenico's suggestion of going vertical and sideways is still going to put all of the antennas broadside to the wind. Instead, how about just aiming them at wind direction (either at it or directly away), horizontally? That way the only wind load would be from the antenna's end-on area, instead of the whole length. This is what I do, and it seems to have worked. If I go vertical, my worry is that the height of the antenna gets to be a good bit longer than the width of the tripod base, and I'm concerned the whole thing will tip over.
But, Domenico does have an interesting idea about aiming at 90-degrees from the wind, but horizontal. That would put the dish edge-on to the wind, at the expense of putting the beams sideways to the wind. Given the modest size of my dish, I would expect that it's not going to be better that way.
How does one calculate such a thing, given that I don't know the manufacturer's wind loading of anything, and don't care to earn a degree in fluid dynamics? Any very simplified back-of-the-envelope way to get a rough idea?
My picture at: http://home.wavecable.com/~ko6th/IMG_0141b6.jpg
Greg KO6TH
----------------------------------------
From: [email protected] To: [email protected] Date: Tue, 2 Sep 2008 18:26:20 +0100 Subject: [amsat-bb] Re: How best to park your satellite antennas
Thanks for all the comments...and apologies for the link error ...it should have read 193.51.107.114
73
Graham
If you look at 193.51.07.114 you can see the sort of array that I am
talking about!
Many thanks
Graham G3VZV _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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participants (5)
-
Edward Cole -
Graham Shirville -
Greg D. -
i8cvs -
Luc Leblanc