IF_average Background Correction Eval

[Alex P]

A 50 Ohm termination resistor ( a near 300K equivalent noise temp source ) 

on the input to the LNA is frequently used for the IF_average Background Correction  

function to linearize the spectral response of the LNA/SDR . An evaluation of the effectiveness of this procedure with regards to potentially adding noise to the data was performed.

Data from a 1m Circular Patch Feed Disk Yagi antenna with a

Nooelec H1 SAWbird and AirSpy Mini SDR using 5 minute data samples were

 obtained from the bright Dec +20 Degree, RA 0615 Hr region .

Individual IF_average *.txt files were processed in MS Excel from both corrected and non-corrected data and converted to a power scale.  The cold_sky background  region was adjusted to 10K and the bright peak scaled to 150K.

The following are the results.

The noise contributed by the 50 Ohm Termination background correction was less than

1K... significantly less than would be shown on normal H Line plots.

( IF_avg V5.01 has enhanced real-time spectral display capability )

Alex Pettit

[Eduard Mol]

Hi Alex, 

Why did you scale the bright peak to 150K? As far as I am aware the brightest HI regions have a brightness temperature of around 100K (based on LAB survey spectra with 5 degree beam width). 

Ed

Op ma 5 okt 2026 om 21:38 schreef 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---
You received this message because you are subscribed to the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sara-list+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/sara-list/fd9ed7a3-ce0e-4307-b092-458ace6e545dn%40googlegroups.com.

[b alex pettit jr]

Hi Ed,

Because I can't access the LAB survey, and did not remember that value, but knew it was no greater than that.

The main purpose being was to show long averages effectively remove the variance on random noise signals.

I also want to compare Open/Short inputs on the LNA and covering the feed with Al Foil.

That last might be an interesting test for your W3 system = is it of any value ?

Thanks,

Alex

=====================================================

[Eduard Mol]

Hi Alex, 

It’s very unfortunate indeed that we lost access to the LAB survey. I used it quite often for planning observations and checking results. 

I suspect that covering the feed with a reflector will cause all sorts of odd reflections and standing waves. I might be wrong though, and there is no cost in trying to find out.

Ed

Op wo 7 okt 2026 om 11:13 schreef 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---
You received this message because you are subscribed to the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sara-list+...@googlegroups.com.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/141800329.778747.1791364384988%40mail.yahoo.com.

[b alex pettit jr]

Covering the Feed with Al Foil probably does not make the first transistor happy,

but I found the method Works for obtaining a background correction file for  the Kraken H1  Disco Feed

which has an integral LNA and its input is not ( reasonably ) accessible .

Alex

On Wednesday, October 7, 2026 at 05:34:04 AM EDT, Eduard Mol <eddiem...@gmail.com> wrote:

Hi Alex,