[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Receiver Noise temperature



Elaborating on the excellent short treatment of weighted sky 
background temperature by Franklin, I would refer Bob to the plotted
absolute sky temperature contours in H. C. Ko, Proceedings of the
IRE, January 1958.
 
>From that data it's evident that large areas of the sky are very 
noisy at frequencies below 400 MHz.  For example the 64 MHz 
map has large portions over 2000 K.  Even at 250 MHz few directions 
are quieter than 100 K.
 
A graph in ITT Reference Data for Radio Engineers has the dispersed
galactic noise (not including the sun and other major point sources)
decreasing with increasing frequency and crossing the 290 K level at
about 180 MHz.  This represents the signal that would be intercepted
by a half-wave dipole on the earth's surface.
 
So I guess the upshot is that by 400 MHz, it starts to get
fairly quiet, but still nowhere near 4 K for an omni antenna.
To approach that it looks like you'll have to go well above 1 GHz.

Hank

   http://www.geocities.com/capecanaveral/3161/hablic.htm
                                               ^
HABLIC: "All balloon launches, all the time" __|


----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home