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



The optimum frequency range in this part of our galaxy starts at 2 GHz where
the cosmic noise level, due to radiation from one or more black holes at the
center of our galaxy, intercepts the thermal noise floor from the "big
bang." The other end of the range is where quantatization noise exceeds
thermal background noise because the photons are too energetic. If I
remember correctly, this is around 100 GHz. If the astrophysicists are
correct about the source of cosmic noise, 1-2 GHz is not the best spot as we
are closer to the edge of this galaxy than the middle and any civilizations
closer to the galactic center would use higher frequencies.

73,

John
KD6OZH

----- Original Message -----
From: "KC6UQH" <kc6uqh@cox.net>
To: "John B. Stephensen" <kd6ozh@verizon.net>; "William Leijenaar"
<pe1rah@yahoo.com>; <amsat-bb@amsat.org>
Sent: Tuesday, February 15, 2005 04:01 UTC
Subject: Re: [amsat-bb] 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
> ----
> 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.
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