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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hi Hans,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>of course I’m familiar with calculating noise figures in
cascaded arrays, but I didn’t investigate the noise figures of the
single stages. You can ‘bypass’ the preamp by adding the 20 dB
pad in front of the preamp and you’ll have similar readouts concerning
SNR reduction. It seems that these readouts are ok, because they correspond
with my MDS, blocking and IM tests I made with external test equipment. <o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>73, Helmut_DC6NY<o:p></o:p></span></p>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>Von:</span><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
h-hartfuss@t-online.de [mailto:h-hartfuss@t-online.de<b>] <br>
</b>Gesendet<b>:</b> Mittwoch, 17. August 2011 10:51<br>
An<b>:</b> Helmut<br>
<b>Cc:</b> hpsdr@lists.openhpsdr.org<br>
<b>Betreff:</b> Re: [hpsdr] Dither on Mercury-EU<o:p></o:p></span></p>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'>Hi Helmut,<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'>I don't think that this is completely
correct. The process is conducted at the ADC by dithering over 2 or 3
quantization steps. Of course this results in an S/R reduction. <o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'>However, the ADC is not the first stage in
the receiver system. The first stage is a low noise preamp with 20 db
gain. <o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'>The overall noise temperature of the receiver
is determined by the noise temperature of the first stage plus a minor
contribution from the second which is the noise temperature of the ADC,
however, divided by the gain of the first. That's cascading rule!<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'>You can easily calculate that it is
almost impossible to increase the overall noise temperature by an order of
magnitude just by increasing the ADC noise figure by say a factor of 4.<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'>73, Hans, DL2MDQ. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt'><span style='font-size:10.0pt;
font-family:"Arial","sans-serif"'><br>
-----Original Message-----<br>
Date: Wed, 17 Aug 2011 09:35:49 +0200<br>
Subject: Re: [hpsdr] Dither on Mercury-EU<br>
From: "Helmut" <dc6ny@gmx.de><br>
To: "'wully'" <wully@bluewin.ch>,
<hpsdr@lists.openhpsdr.org><br>
<br>
***** High Performance Software Defined Radio Discussion List *****<br>
<br>
Hi Alfred,<br>
<br>
enabled dithering reduces the signal-noise-ratio at least by 6-10 dB. If<br>
less, something is wrong with the efficiency of dithering. My two<br>
mercuries-eu show similar values.<br>
<br>
73 Helmut, DC6NY<br>
<br>
<br>
PS: Perhaps we meet us 40m to continue<br>
<br>
<br>
-----Ursprüngliche Nachricht-----<br>
Von: hpsdr-bounces@lists.openhpsdr.org<br>
[mailto:hpsdr-bounces@lists.openhpsdr.org] Im Auftrag von wully<br>
Gesendet: Mittwoch, 17. August 2011 09:07<br>
An: hpsdr@lists.openhpsdr.org<br>
Betreff: [hpsdr] Dither on Mercury-EU<br>
<br>
***** High Performance Software Defined Radio Discussion List *****<br>
<br>
Hi all<br>
<br>
First, I would like to add my congratulations for Phil Harman for this <br>
award!<br>
<br>
I have noticed a strange behavior of Mercury-EU, which might indicate an <br>
individual board failure:<br>
<br>
Antenna input with 50 Ohms terminated, no antenna. When switching on <br>
Dither I notice an increase in background noise level of between 7 and <br>
11 dB depending on the band! Typical noise value without dither is <br>
around -130dBm (slightly better than tapr-mercury).<br>
<br>
Doing the same experiment on my two Tapr-Mercuries, the increase of <br>
noise is hardly noticable with a value of 1 dB.<br>
<br>
Since I don't have two Mercury-EU, I can not compare.<br>
Normally, I am running the HPSDR with Dither off, so this is only a <br>
"theoretical" problem, but it is interesting anyway.<br>
<br>
Any suggestions are much appreciated.<br>
<br>
73, Alfred, HB9EPU<br>
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