[amsat-bb] Re: ISS HamTV Frequencies (range gain)

[Fabio Azzarello]

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 at 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 at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Art McBride
> Sent: Monday, May 13, 2013 12:44 AM
> To: 'Roger'; amsat-bb at 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 at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Roger
> Sent: Sunday, May 12, 2013 2:34 PM
> To: amsat-bb at 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
> >
> >
>
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