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Re: re: QRM 2m, question for sat builders



The optimum Frequency for SETTI is 1 to 2 GHz this is where the decreaase in
niose and the loss from using a higher frequency cross over.

Art KC6UQH

----- Original Message -----
From: "John B. Stephensen" <kd6ozh@verizon.net>
To: "William Leijenaar" <pe1rah@yahoo.com>; <amsat-bb@amsat.org>
Sent: Monday, February 14, 2005 11:55 AM
Subject: Re: [amsat-bb] re: QRM 2m, question for sat builders


> Higher frequencies are advantageous for downlinks as cosmic noise
decreases
> at 6 dB per octave and less power is needed at the satellite. For digital
> amateur satellites licensed in the U.S. there is a bandwidth limitation is
> 20 kHz on 2 meters and 100 kHz on 70 cm. Downlinks usually need to be
faster
> than uplinks.
>
> 73,
>
> John
> KD6OZH
>
> ----- Original Message -----
> From: "William Leijenaar" <pe1rah@yahoo.com>
> To: <amsat-bb@amsat.org>
> Sent: Monday, February 14, 2005 18:39 UTC
> Subject: [amsat-bb] re: QRM 2m, question for sat builders
>
>
> > Hi AMSATs,
> >
> > >I have a question for those "in the know" (this means
> > I'm not interested in
> > >speculation). Why are so many of the newer LEOs
> > designed as Mode J? Is it due
> > >to the commercialization of the Microsat design? More
> > commercial downlinks
> > >available in the UHF range? Harmonic suppression at
> > the satellite end? I truly
> > >wonder what the impetus towards J is....
> >
> > There are several reasons for this:
> >
> > - Bigest reason is that with MODE-J you have no
> > problem with the 3rd harmonics of
> >   the transmitter. This makes your receiver overloaded
> > and less sensitive without
> >   any good filter at the TX side. Its a real serious
> > problem.
> > - Then on 70cm there is much more bandwidth available
> > than on 2m. An downlink on
> >   70cm makes the change smaller of having downlink
> > interference of 2 satellites.
> > - For the groundstation you also need to have more ERP
> > on 70cm compared with 2m.
> >   This is because of more path losses. More power on
> > 70cm is more complicated than
> >   on 2m because of more cable losses, more expensive
> > amplifiers etc...
> >
> > Ofcourse there are also disadvantages with MODE-J
> > like:
> >
> > - Higher downlink doppler effect.
> > - You need a good RX, often LNA is needed and more
> > gain antennas
> > - At the groundstation you need MODE-J filter to avoid
> > TX to RX interference
> >
> > The disadvantages with MODE-J on the groundstation are
> > actually the same as on the
> > satellite with MODE-B.
> >
> > Just wait for P3e, it will have MODE-UV (the old
> > MODE-B) :o)
> >
> > 73 de PE1RAH, William
> > ---
> > All your favorites on one personal page - Try My Yahoo!
> > http://my.yahoo.com
> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
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