At 09:16 AM 9/2/2008, i8cvs wrote:
----- Original Message ----- From: "Graham Shirville" g.shirville@btinternet.com To: amsat-bb@amsat.org 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: dubususa@hotmail.com *****************************************************