RE: [SARA] System Equivalent Noise Temp ?

[edhar...@gmail.com]

What you are measuring is the variability of the system noise in your image, not the system temperature.

 

We have the following sources:

 

1. Antenna noise due to spillover from the receiver.
2. LNA noise (The good news is this pretty much sets the noise level for the system.)
3. “Other”

 

A rough guess is an LNA with 1dB noise is about 75K.  Lower noise figures on some amplifiers are claimed but the price skyrockets.  (Some claims are exaggerated as well. :<)

 

An interesting slide deck from NRAO (Scott Ransom) “Radio Astronomy: Sensitivity and Noise” is located here:  https://events.asiaa.sinica.edu.tw/school/20160815/talk/sransom0818.pdf

 

It covers a lot of the basics.  Slide 22 shows all of the contributions to the system noise (including source intentional and non-intentional).  (When looking at his receiver temperature, remember he is describing professional equipment where the receiver costs more than most houses… often the entire subdivision.)

 

All of that said, that variability is a LOT more important to amateurs like ourselves.  A system with a stable system temperature is worth more than a quiet system temperature that is unstable.  Your plot shows a pretty stable system (to me).

 

Ed Harfmann

 

From: 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Friday, April 17, 2026 6:29 AM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] System Equivalent Noise Temp ?

 

Not sure this is meaningful or not ?

 I plotted an  hours worth of data from my 1.2m dish during a period 

of minimum H1 brightness :

Dec +40 dg over the RA times 11:30-12:30 

 

I used the Argelander H1 profile calculator to plot the expected H1 levels and compared

that to my data ..

 

comments ?

 

Thanks,

Alex 

 

 

 

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[Alex P]

Hello Ed,

Yes, I attempted to Delete the post, evidently Not.

It is just the RMS noise level proportional to the averaging time.

Thanks,

Alex

[Steve Hallman]

Hi Alex;

Here are my comments ...

Using the LAB Simulation HLine projection to determine a radio telescope's "Responsivity [K / DN]" should work

But be cautious about doing calculations in dB, it's easier to stick with power

My attempt to do a radio telescope calibration are here: SARA RTOP March 2026 @ 1Hr:19Mins:30Sec

https://youtu.be/dF0k1VCrrbI?si=vBnuFGDX6oUCVTWi

Miracles of Science... Benefiting all Humanity

On Fri, Apr 17, 2026, 3:29 AM 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Not sure this is meaningful or not ?

 I plotted an  hours worth of data from my 1.2m dish during a period 

of minimum H1 brightness :

Dec +40 dg over the RA times 11:30-12:30 

I used the Argelander H1 profile calculator to plot the expected H1 levels and compared

that to my data ..

comments ?

Thanks,

Alex 

[Marcus D. Leech]

On 2026-04-17 08:15, edhar...@gmail.com wrote:

What you are measuring is the variability of the system noise in your image, not the system temperature.

 

We have the following sources:

 

1. Antenna noise due to spillover from the receiver.
2. LNA noise (The good news is this pretty much sets the noise level for the system.)
3. “Other”

 

A rough guess is an LNA with 1dB noise is about 75K.  Lower noise figures on some amplifiers are claimed but the price skyrockets.  (Some claims are exaggerated as well. :<)

LNAs that offer considerably below 1dB noise figure are readily available--the NooElec SawBird H1+ for example routinely delivers better than
  advertised (about 0.8dB claimed, with about 0.7dB delivered).  The "Hydrogen Feed Arm" for the discovery dish (which can be adapted to other dishes)
  also delivers well below 1dB noise figure.  The folks selling kit into this particular hobby know that we're not stupid.   IT IS true that companies selling
  consumer LNBFs *routinely* make the wildest possible claims on the noise figure of their gear.   I've seen Ku-band LNBFs advertised with noise figures of
  0.1dB, and when you look into their parts lineup, they cannot possibly deliver better than 1dB.

[b alex pettit jr]

I'd like to thank Everyone for their useful input.

The Title may have been a misnomer, but I am quite impressed with the low signal level ability of the System.

FYI it uses Tom Henderson ( WD5AGO ) 1st  LNA (0.35nf) > 1stage Cavity Filter > 2nd LNA hardware.

This is the first time I examined the Dark RA12 part of a drift scan.

`

Regards,

Alex Pettit