Re: a question about the antenna VERT2450


#1

Hello, Erric

Could you tell me the effective noise temperature for VERT2450? I have
searched the mailing list, but there is no answer for it. Thank you!

Bill


From: Bill S. removed_email_address@domain.invalid
To: removed_email_address@domain.invalid
Sent: Tuesday, April 21, 2009 6:48:34 PM
Subject: [Discuss-gnuradio] a question about the antenna VERT2450

Hello,

I have a simple question about the antenna effective noise temperature
for VERT2450. Does anybody know its effective noise temperature? Thanks
a lot! I hope Ettus could let me know.

Thanks!

Bill


#2

Bill,

The short answer is that there is no answer to your question.

The long answer is that noise temperature is a function of where you
point the antenna, and the ambient noise environment. It is also not
normally specified for low gain antennas, only for dishes and the like.

I would suggest that you read the Wikipedia article on noise
temperature.

Matt


#3

Hi, Matt

I have read that Wiki article and got it! The noise temperature of that
antenna could be ignored. Thank you!

Bill


From: Matt E. removed_email_address@domain.invalid
To: Bill S. removed_email_address@domain.invalid
Cc: removed_email_address@domain.invalid
Sent: Wednesday, April 22, 2009 8:01:48 PM
Subject: Re: [Discuss-gnuradio] a question about the antenna VERT2450

Bill,

The short answer is that there is no answer to your question.

The long answer is that noise temperature is a function of where you
point the antenna, and the ambient noise environment. It is also not
normally specified for low gain antennas, only for dishes and the like.

I would suggest that you read the Wikipedia article on noise
temperature.

Matt


#4

Matt E. wrote:

Matt

Even for dishes, you have to factor in the feed assembly as well (a dish
with a 15dB edge taper feed will have a lower spillover noise than
one with the standard 10dB edge taper).

Ground noise should only be a problem due to spillover, and a mesh
surface that isn’t well-matched to the wavelength of interest.

The ground is a blackbody radiator with an equivalent noise temperature
of about 300K, and how much of this noise leaks
into your feed determines what the effective noise temperature is of a
parabolic reflector antenna. A feed with an aggressive
edge taper, and a good solid-surface dish should push the ground noise
down to under 5K.

For a low-gain antenna, it just isn’t relevant. The antenna “sees” all
noise sources within its 3dBi “torus”. It’s rather similar for
amplifiers in the HF bands. The ambient noise temperature is so high
(100,000K) in HF that specifying the noise temperature of the
amplifier just isn’t meaningful.

Marcus L.
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org