SNRs for H-Line different dish sizss

[Andrew Thornett]

Hi All,

Maybe this table is useful for comparison effect changing size dish for H-Line work.

Andy

[kb3puw]

I did a study of my 1 Meter Nooelec Mesh dish and a 2 Meter umbrella under near identical conditions.  The peak above baseline for the 2 meter was 4 times bigger than the 1 meter dish - but my measured Tsys was very different between the two.

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[Conrad Cardano]

Hi

Thank you very much for this.  I am new to SARA, but have not purchased a 21cm setup yet.  

The "scope in a box" is very interesting, but I would also like to consider something larger(if possible).

If there are any books that would be helpful in Ha radio astronomy, I would appreciate the recommendation.

Conrad

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[Alex P]

Differences in amplitude are calculated by Subtracting  dB values ...

And, 3 dB = a doubling in Power, 6 dB a doubling in Amplitude

[b alex pettit jr]

perhaps that should be phrased : Differences are Calculated ......

[b alex pettit jr]

0.5 dB = 10^(0.5/10) = 1.122 : 1 Power Ratio

1.7 dB = 10"(1.7/10) =  1.479 : 1 Power Ratio

=   47.9 % being 4X greater than 12.2 % above background 

[Andrew Thornett]

Those real world figures seem to agree with the CSV file I posted, extract attached again hear = SNR for 2m = 4x for 1m dish on this CSV file, so I am very pleased to see that the theoretical calculations reflect the real world - thanks for posting your data.

Andy

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From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Friday, October 31, 2025 12:04:16 AM
To: 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] SNRs for H-Line different dish sizss

 

perhaps that should be phrased : Differences are Calculated ......

Differences in amplitude are calculated by Subtracting  dB values ...

And, 3 dB = a doubling in Power, 6 dB a doubling in Amplitude

 

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[b alex pettit jr]

Here is data from my 1.2 meter dish :

[Andrew Thornett]

2.57 dB = 1.435x greater than 1 dB. Therefore your 1.2m is performs with SNR 43.5% 》reference with 1 dB performance.

My table (attached again) places difference between 1.2m dish and 1m dish as 44%, sometimes again your real world tests, Alex, with your 1.2m dish agree with the theoretical performance- amazing! Worth saying the theoretical table assumes everything works 60% efficiency, which again seems to be proven here to match the best possible in real world scenarios. 

Andy

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From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

Sent: Friday, October 31, 2025 9:40:23 AM
To: 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

Subject: Re: [SARA] SNRs for H-Line different dish sizss

Here is data from my 1.2 meter dish :

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[b alex pettit jr]

Andrew,

I do not understand the "1 dB" reference :

0 dB =  a 1 : 1.000 power ratio

1 dB =  a 1 : 1.259 power ratio

[Andrew Thornett]

My table presents results relative to 1m dish at 1dB

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Subject: Re: [SARA] SNRs for H-Line different dish sizss

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[b alex pettit jr]

Test Data

[Andrew Thornett]

Ahhhh.........

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Sent: Friday, October 31, 2025 11:31:08 AM

To: 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] SNRs for H-Line different dish sizss

Test Data

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[b alex pettit jr]

From processing data acquired by dishes up to 12.0 meters,

about +3B over cold sky is the max from a distributed source as Galactic H Clouds

[b alex pettit jr]

12 m Radio Telescope @ Neu Golm Observatory,  Germany