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

Mon May 13 05:52:27 PDT 2013

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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