Changing coaxial cable on 21cm circular Yagi at ObsMEV 2024/12/31

[Richard Squirrel]

Greetings and best stellar wishes to everyone.

I see that I am not the only one wanting to make cable improvements and getting tangled up in them!

I also took advantage of the holidays with my astro buddy to carry out a mechanical and electronic update of my 21 cm installation.
The modification of the mechanical part now allows us to mount the antenna at wide angles without obstruction and are not the issue.
Unfortunately, I changed also too many things at once and I have difficulty understanding what would explain the changes in the data received.

The data isn't that different but there are some weird things and I don't have the experience or hardware to figure out the source, so I would like to ask your opinion.

Until now my acquisition line was composed of:

And now :

The cables have been changed to low loss models (and $much$ more painful to shape! ... greetings to a certain "Alex" on this list!)
Unfortunately, the LNA was also exchanged, because it was easier to prepare the boxes in advance in a warm place before disassembly on the field.
As we are going to point south again, there is also the antenna which has been rotated along the roll axis by 180° to keep the sma facing down.

I add that I have two SMAs on the antenna, one for the output and one with a 50 ohm load.

Before at 70° North I had the signal level différence which was increasing with the frequency:

https://radiomev.obsstjean.fr/show_radio.php?session=ObsMEV_Nord_70deg_20241230&start=5

And now at 80° North, I have the signal level difference which is decreasing with the frequency:

https://radiomev.obsstjean.fr/show_radio.php?session=ObsMEV_Nord_80deg_20241231_16&start=5

This does not seem to be related to the antenna flip, as I have measurements to the south on the same side which have a signal in the same direction as before:

I wonder if this is not due to the change of the LNA, but it is the same model, so I find it strange between two identical models ?

Regarding the reception chain, I theoricaly got +4 dB of level and probably a little less noise with the small low loss cable at the head of the LNA.

When I look at the processed data, I don't have the impression of having improved the SNR especially for low levels, as there are mode "black" pixel before :

Before :

https://radiomev.obsstjean.fr/show_radio.php?session=ObsMEV_Nord_70deg_20241230&start=16

After :

https://radiomev.obsstjean.fr/show_radio.php?session=ObsMEV_Nord_80deg_20250101&start=14

Unfortunately ezRA always talks in level ratio and I have trouble finding how to compare the absolute levels and the dynamics before and after the change.

We also changed the drift angle from 70° to 80° and what we look at as a signal is quite different, so I'm a little lost to compare that.

I already know that the signal is stronger because on the data fusion with the 80° scan is more energetic than the others, I think that this will cause me problems during the fusion:

https://radiomev.obsstjean.fr/show_radio.php?session=ObsMEV_2024_Fusion_in_progress&start=146

I don't know if I should put the old LNA back and if I have improved or degraded the reception chain ?

Please note that I do not have easy access to the setup to do tests and that I cannot put the software that I would like because it is a Linux installed with ezRA only to be stable in production.

Thank you for any leads on ezRA and advice you could give me.

Richard

[Alex P]

Hello Richard,

Unfortunately ezRA always talks in level ratio and I have trouble finding 

how to compare the absolute levels and the dynamics before and after the change

The advantage of the Windows based AirSpyStudio SDR# & IFAvg &  HLine3D software 

is that the plots are referenced to Cold Sky and Calibrated and Amplitudes can be compared.

Alex

[b alex pettit jr]

This plot was done using AirSpyStudio SDR# ,  IFAvg & Excel

[Richard Squirrel]

Hi Alex,

I have noted your method in my todo list.
I plan to try AirSpyStudio SDR and install the IFAvg plugin on another windows machine.
I also need to test if it is compatible with an RTL-SDR version 4 which only accepts specific drivers.

In the meantime, does anyone know if the raw data recorded by ezRa:

# time + frequency spectrums of RMS power = sqrt(mean of sum of squares)
2024-12-26T00:00:14 x x x x x x x x x x ...
can be converted to a format that allows for a reference to Cold Sky to be retrieved as you said?

The other way around I know that ezColIFAvg.py does the trick.

Thank's.

Richard

[b alex pettit jr]

Richard,

  SDR# is compatible with the RTL units.

https://www.rtl-sdr.com/cheap-and-easy-hydrogen-line-radio-astronomy-with-a-rtl-sdr-wifi-parabolic-grid-dish-lna-and-sdrsharp/

Alex

[andrew....@googlemail.com]

I can answer the first question = “I also need to test if it is compatible with an RTL-SDR version 4”

 

Answer = yes it is! As I have the 2 working together at LRO.

 

Andy

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[Richard Squirrel]

Thank's Andy.

I had some strange behaviors with the V4 at first on my Linux following the ezRA installation documentation.

It worked a little, but not for everything.
I had to import the drivers from RTL-SDR and compile it. Then it went back to normal.
So I'm a little suspicious with V4.

Richard

[b alex pettit jr]

  RTLSDRV4 Software info

Richard

-

[Andrew Thornett]

I don't have experience using these RTL SDR dongles with Linux as I use cheap second hand Windows miniPCs off eBay to run my radio astronomy experiments in my shack, so can't help there. Sorry!

Certainly both RTL SDR V3 and V4 work well with latest version of SDR# on Windows.

The drivers for the RTL SDR dongles are also readily available - for Windows at least.

Andy

Sent from Outlook for Android

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From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Friday, January 3, 2025 10:10:32 AM
To: sara...@googlegroups.com <sara...@googlegroups.com>

Subject: Re: [SARA] Re: Changing coaxial cable on 21cm circular Yagi at ObsMEV 2024/12/31

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[Jim Brown]

So the plot is in Excel but what software collected the data to import to Excel?

On 1/2/2025 21:27, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

This plot was done using AirSpyStudio SDR# ,  IFAvg & Excel

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Hawk's Nest Radio Astronomy Observatory
http://hnrao.weebly.com/

[b alex pettit jr]

AirSpyStudio SDR#  &    IFAvg plug-in

For more info see  21cm_Step2

Thanks,

Alex

GitHub - AP-HLine-3D/HLine3D: Beginners Low Cost 21cm Radio Telescope Project

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