One needs to also realize duration. The time say above 70 degree elevation (where rates are highest) are less than 2% of the total pass times. Not worth worrying about. Similarly, a LEO satellite spends 70% of its time below about 22 degrees. (but it is far away and needs max gain). So simply design for the best operation for most of the time when the link will work.
Remember, the satellite is 3000 km away on the horizon and very weak, but as it gets into say 1500 km it is twice as close and 4 times (6 dB) stonger which is a heck of a lot of gain. When it goes directly overhead it is another 6 dB closer which is more than *ten* times the signal on the horizon, so don't worry about the 2% of the time it is going to be above 70 degrees. The signa is 10 times stronger and easy to deal with.
Bob, WB4APR
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Art McBride Sent: Monday, May 13, 2013 12:44 AM To: 'Roger'; amsat-bb@amsat.org Subject: [amsat-bb] Re: ISS HamTV Frequencies
Roger, A SWAG, (Wild Guess) 1 degree per second at a Zenith of 90 degrees. Anything less than 90 degrees will be slower with several minutes spent near the horizon. You can use an orbital program to get exact numbers. With a wide beam width antenna, the lag overhead may never require the antenna to move with the object, as there will be time for the antenna system to catch up after passing overhead. Art, KC6UQH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Roger Sent: Sunday, May 12, 2013 2:34 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: ISS HamTV Frequencies
Anybody off the top of their heads know how many degrees a second swing are (is?) required for direct aim at the ISS? I know there are beam width tolerances, altitude variations and degree above horizon variations but I'm looking at Bob B's fixed antenna aiming of 15-20 degrees above horizon to evaluate swinging a dish without torque eating up the drive train...
Roger WA1KAT On 5/12/2013 5:01 PM, M5AKA wrote:
The AMSAT-UK page at http://amsat-uk.org/2013/05/12/hamtv-from-the-iss/
provides the links, they are:
Facebook https://www.facebook.com/Hamtvproject
More information at http://www.amsat.it/Amsat-Italia_HamTV_brochure.pdf and http://www.amsat.it/Amsat-Italia_HamTV.pdf
The HamTV.pdf gives the link budget, looks like there's 7dB of
coax/connector losses to overcome between the ISS transmitter and the antenna. That document indicates a 90cm dish should be sufficient.
I believe that it's going up on ATV 4 which is currently slated for June
5.
73 Trevor M5AKA
_______________________________________________ Sent via AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
Hi all, 1 or 2 degree per second is an educated guess for almost all passes. If the pass is "over head" the speed will increase up to 4/5 degree per second (as maximum value), such a speed is not achievable by all rotators.
Hope that helps, 73s
Fabio IZ5XRC www.amsat.it
On Mon, May 13, 2013 at 2:52 PM, Robert Bruninga bruninga@usna.edu wrote:
One needs to also realize duration. The time say above 70 degree elevation (where rates are highest) are less than 2% of the total pass times. Not worth worrying about. Similarly, a LEO satellite spends 70% of its time below about 22 degrees. (but it is far away and needs max gain). So simply design for the best operation for most of the time when the link will work.
Remember, the satellite is 3000 km away on the horizon and very weak, but as it gets into say 1500 km it is twice as close and 4 times (6 dB) stonger which is a heck of a lot of gain. When it goes directly overhead it is another 6 dB closer which is more than *ten* times the signal on the horizon, so don't worry about the 2% of the time it is going to be above 70 degrees. The signa is 10 times stronger and easy to deal with.
Bob, WB4APR
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Art McBride Sent: Monday, May 13, 2013 12:44 AM To: 'Roger'; amsat-bb@amsat.org Subject: [amsat-bb] Re: ISS HamTV Frequencies
Roger, A SWAG, (Wild Guess) 1 degree per second at a Zenith of 90 degrees. Anything less than 90 degrees will be slower with several minutes spent near the horizon. You can use an orbital program to get exact numbers. With a wide beam width antenna, the lag overhead may never require the antenna to move with the object, as there will be time for the antenna system to catch up after passing overhead. Art, KC6UQH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Roger Sent: Sunday, May 12, 2013 2:34 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: ISS HamTV Frequencies
Anybody off the top of their heads know how many degrees a second swing are (is?) required for direct aim at the ISS? I know there are beam width tolerances, altitude variations and degree above horizon variations but I'm looking at Bob B's fixed antenna aiming of 15-20 degrees above horizon to evaluate swinging a dish without torque eating up the drive train...
Roger WA1KAT On 5/12/2013 5:01 PM, M5AKA wrote:
The AMSAT-UK page at http://amsat-uk.org/2013/05/12/hamtv-from-the-iss/
provides the links, they are:
Facebook https://www.facebook.com/Hamtvproject
More information at http://www.amsat.it/Amsat-Italia_HamTV_brochure.pdf and http://www.amsat.it/Amsat-Italia_HamTV.pdf
The HamTV.pdf gives the link budget, looks like there's 7dB of
coax/connector losses to overcome between the ISS transmitter and the antenna. That document indicates a 90cm dish should be sufficient.
I believe that it's going up on ATV 4 which is currently slated for June
73 Trevor M5AKA
Sent via AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
participants (2)
-
Fabio Azzarello -
Robert Bruninga