Different Spectrum Analyser with different RSP's?

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Different Spectrum Analyser with different RSP's?

Post by glovisol » Thu Apr 11, 2019 6:06 am

Hi Steve,

First of all I confirm that low frequency performance down to 100 KHz is is excellent, as demonstrated by the enclosed pics., which I have already uploaded here:

https://www.sdrplay.com/community/viewt ... 3&start=70

The reason why I upload them again here is to allow comparison between noise scans taken with the Spectrum Analyser software with the RSP-1A and the RSPduo. The filter is the same, the settings are the same, the noise generator is the sane, only the RSP is different and there are significant differences in the display, which would seem to be caused only by different characteristics in the RSp's. Below are scans with RSP-1A. In the next post those taken with RSPduo.
Attachments
LF&MF Elim. Filter 1.RSP-1A.jpg
LF&MF Elim. Filter 1.RSP-1A.jpg (143.4 KiB) Viewed 2878 times
LF&MF Elim. Filter 2.RSP-1A.jpg
LF&MF Elim. Filter 2.RSP-1A.jpg (137.82 KiB) Viewed 2878 times
LF&MF Elim. Filter 3.RSP-1A.jpg
LF&MF Elim. Filter 3.RSP-1A.jpg (160.82 KiB) Viewed 2878 times

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glovisol
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Location: Piedmont, Italy

Re: Different Spectrum Analyser with different RSP's?

Post by glovisol » Thu Apr 11, 2019 6:08 am

This looks very strange to me and I look forward to your comments.

Kind regards,

Gianfranco
Attachments
LF&MF Elim. Filter 4.RSP duo.jpg
LF&MF Elim. Filter 4.RSP duo.jpg (142.47 KiB) Viewed 2877 times
LF&MF Elim. Filter 5.RSPduo duo.jpg
LF&MF Elim. Filter 5.RSPduo duo.jpg (139.15 KiB) Viewed 2877 times

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g1hbe
Posts: 494
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: Different Spectrum Analyser with different RSP's?

Post by g1hbe » Thu Apr 11, 2019 7:42 am

If you mean the difference in displayed noise, haven't you got the averaging on in the second shot?

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Andy

glovisol
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Re: Different Spectrum Analyser with different RSP's?

Post by glovisol » Thu Apr 11, 2019 7:48 am

Hi Andy,

As you will see in the next post, this is a much bigger difference than a question of averaging: if you look carefully, you will discover:

a) The filter slope has changed in frequency response and
b) The attenuation range has lost 10 dB.

The explanation is quite simple, as you will realise reading below.

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glovisol
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Re: Different Spectrum Analyser with different RSP's?

Post by glovisol » Thu Apr 11, 2019 8:14 am

Hi Steve,

The difference in the behaviour of the RSP-1A and the RSPduo is due to the fact that while the frequency response of the RSP-1A is flat, the response of the RSPduo has a high pass characeristic, as you can see in the pics below. NOW I DO NOT WISH TO BE MISUNDERSTOOD:

Rated frequency response of the RSPduo on coax channel of Tuner 1 goes down to 1KHz, so there must be some bug that unexpectedly turns the MW notch on when the Spectrum Analyser software is being used. I am posting pics for the RSP-1A and for the RSPduo for comparison. These pics are self-explanatory.

Kind regards,

Gianfranco
Attachments
RSP1A_dynamic range.jpg
RSP1A_dynamic range.jpg (245.21 KiB) Viewed 2856 times
RSPduo_LF input characteristic.jpg
RSPduo_LF input characteristic.jpg (259.61 KiB) Viewed 2856 times
RSPduo enlarged.jpg
RSPduo enlarged.jpg (250 KiB) Viewed 2856 times

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SteveAndrew
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Joined: Thu Nov 16, 2017 11:06 pm
Location: Gold Coast, QLD, Australia

Re: Different Spectrum Analyser with different RSP's?

Post by SteveAndrew » Thu Apr 11, 2019 10:43 am

Hi Gianfranco

I've found a problem with the gain settings and filters not being set correctly at startup for the SDRduo. Yas - JA8SCD has reported similar problems. I'm working on the problem now and will post a note when I have a result.

Steve

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glovisol
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Re: Different Spectrum Analyser with different RSP's?

Post by glovisol » Thu Apr 11, 2019 12:49 pm

Thanks, Steve. Will carry on testing & let you know about other results.
Gianfranco

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