Forum: GNU Radio Re: a question about the antenna VERT2450

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Bill S. (Guest)
on 2009-04-23 03:54
(Received via mailing list)
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
Matt E. (Guest)
on 2009-04-23 04:02
(Received via mailing list)
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
Bill S. (Guest)
on 2009-04-23 05:17
(Received via mailing list)
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
Marcus D. Leech (Guest)
on 2009-04-23 05:48
(Received via mailing list)
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
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