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Re: Re: RE: Geo Opportunity



The ionosphere does shield us from galactic noise up to about 30 MHz. When
10 meters is open the primary noise contribution is from atmospherics
(lightning storms). When the band is closed the primary noise source is
galactic noise with a tiny bit of atmospheric noise. 18 dB of noise for
terrestrial stations is the best case. It is usually higher.

The galactic noise numbers are for an ominidirectional antenna so there is
not much that you can do about it at HF with a small spacrecraft.

73,

John
KD6OZH

----- Original Message -----
From: "Bob Bruninga" <bruninga@usna.edu>
To: "John Stephensen" <kd6ozh@AMSAT.Org>
Cc: "Keith N6ORS" <k2@pe.net>; "amsat" <amsat-bb@AMSAT.Org>
Sent: Thursday, July 31, 2003 04:35
Subject: Re: [amsat-bb] Re: RE: Geo Opportunity


> >  On Thu, 31 Jul 2003, John Stephensen wrote:
> >
> > > There is background noise at GEO generated by the black hole(s) at the
> > > center of our galaxy. At 28 MHz it is about 17 dB above thermal noise
> > > at 290 K.
>
> I need to understand this more.  IN previous emails you mention
> atmospherics at 28 MHz as being +18 dB above 300K.  Now you are saying
> that there is also a +17 dB contribution from exo-atmospheric sources as
> well?
>
> My experiences with sky noise have always been with pointing a high gain
> beam or dish at the galactic center.  Yes, then you can hear it.  But
> these are also at 2m and above.  I guess we dont hear it down at 28 MHz
> usually because it is masked by the 18 dB of atmosphereic noise.
>
> But if what you say is true, then it sounds like 10m wont work as a 14 dB
> path loss advantage as an uplink any more at geo than it does on the
> ground..   Please confirm.
>
> de WB4APR, Bob
>
>
>


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