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Re: Trying AO-40



Ed:

Thanks for your comments about Doppler being positional as well as
rotational dependent. That is an excellent point.

I'm not an orbital analyst either - I was kind of hoping one of them would
wade in also.

I was reading this morning about TCA on elliptical orbit satellites - the
info I read said TCA "could occur at either AOS or LOS" - so this is
another factor that effects Doppler based on position - I seem to remember
the wheel was only good for certain MA's so this must be why.

73's

Don Woodward
KD4APP
AMSAT 33535
kd4app@amsat.org
http://kd4app.webhop.org


----- Original Message ----- 
From: "Edward R. Cole" <al7eb@ptialaska.net>
To: "Amsat Bulletin Board" <amsat-bb@AMSAT.Org>
Sent: Monday, June 02, 2003 15:35
Subject: Re: [amsat-bb] Trying AO-40


Don,

That is why the circular calculator is so nice....it estimates satellite
Doppler as a function of MA.  What I haven't seen discussed here is the
fact that not only is there Doppler due to the orbital movement of AO-40
but there is earth rotational Doppler and all Doppler effects vary with
your latitude.  The circular calculator probably doesn't take into account
earth rotation so there is a small error due to this.  Also we are only
taking into account S-band Doppler and your uplink has Doppler too.  The
complete mathematical problem is pretty complex!  Fortunately, 70cm Doppler
effect is much smaller so one can usually find themselves quickly if they
have the S-band tuned in.  L-band will have three times higher Doppler
effects!  K-Band is really a difficult one!!!

I'm not an orbital analyst so any experts are welcomed to wade into this
discussion...;-)

73 - Ed

At 10:51 AM 6/2/03 -0400, Don Woodward wrote:
>No your chart does not include all usable portions - when Doppler is in
>effect the frequencies slide and all portions shown on my chart per the
>published passband are available under the correct Doppler conditions. The
>S-band frequencies in your chart and mine are the frequency that the
>Satellite is transmitting on and not the frequency you receive on after
>Doppler correction - the U-band TX frequencies in your chart and mine are
>the frequencies that the ground station transmits on.
>
>When you tune in the beacon with Doppler it's not going to display
2401.323
>on your receiver but the uplink on your end will be 435.667 for the
>beacon - so the bands are offset to allow compensation for Doppler - your
>chart and mine _only_ display the frequencies at TCA when there is no
>Doppler.
>
>73's
>
>Don Woodward
>KD4APP
>AMSAT 33535
>kd4app@amsat.org
>http://kd4app.webhop.org
>
>
>----- Original Message ----- 
>From: "David Rush" <david@davidarush.com>
>To: <amsat-bb@AMSAT.Org>
>Sent: Monday, June 02, 2003 10:06
>Subject: Re: [amsat-bb] Trying AO-40
>
>
>Don:
>
>>Your chart does not include the entire passband.
>
>But it does include all of the "intersection" of the published passbands,
>doesn't it?  So it includes the usable portion of the transponder, which
is
>my intent.
>
>>A correct chart which has been published for a long time is at
>>http://www.sunsunsun.net/kd4app/ao40/conversion.htm which includes the
>>whole passband.
>
>Nice chart.  Wish I'd found it a week ago!
>
>73,
>David, ky7dr
>
>
>----
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>
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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