<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi Helmut, <div><br></div><div>Yes, I agree, the situation is an unfortunate one that has caused and apparently still causes confusion among HPSDR users. On this reflector there has been much discussion of the pros and cons concerning how the control should be labeled so I hope I don't cause yet another series of unnecessary discussions concerning the issue by answering your question. </div><div><br></div><div>I continue to maintain that the proper label for the front panel control is "ATTEN", not "PREAMP", as we DO NOT turn any pre-amp on or off in Mercury, instead we are inserting or removing an internal pad in between the antenna connector and the rf amplifier ahead of the ADC chip in the Mercury receiver by using the control. </div><div><br></div><div>As you point out, yes, if the 20 dB pad is selected the noise figure of the receiver will be degraded by 20 dB and your noise floor will rise 20 dB, unless you have external signals (atmospheric noise, for example) at the Mercury input connector that are quite large. Now whether that is important to you or not depends upon how you use your Mercury receiver, especially what frequencies/bands you use. </div><div><br></div><div>If you spend all you time on relatively low frequency bands where atmospheric noise is normally the dominant noise-limiting parameter for your receiving system, then switching the 20 dB pad "in" may help you substantially by preventing overload signal conditions from occurring in Mercury and you will not notice an increase in your noise floor when inserting the pad. However, if you are operating on bands, say 20 meters and higher in frequency, the noise-limiting parameter for your receiving system will normally NOT be atmospheric noise but rather it will be noise generated by the receiver itself (or antenna). In this case you dramatically hurt your sensitivity to weak signals (by 20 dB, in fact!) by inserting the attenuator and you will see an obvious 20 dB rise in the noise floor level when the pad is inserted. </div><div><br></div><div>What you choose to call the front-panel control is not too important of course as long as you, the operator, understand what the control is actually doing. The fact is that the control is inserting the 20 dB pad or removing the 20 dB pad, so the less confusing label in my view is "ATTEN", and I therefore label my PSDR versions accordingly as "ATTEN". I think Doug W5WC uses "ATT" for the label and sometimes I keep that label but it means exactly the same thing, namely, ATTENUATOR. </div><div><br></div><div>I hope this explanation helps you understand the issue better and doesn't generate much more discussion over this technically trivial matter. </div><div><br></div><div>73, Joe K5SO</div><div><br></div><div><div>On Sep 17, 2011, at 8:45 AM, Helmut Oeller wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">***** High Performance Software Defined Radio Discussion List *****<br><br> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> <meta name="Generator" content="Microsoft Word 12 (filtered medium)"> <style> <!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4;} @font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {margin:0cm; margin-bottom:.0001pt; font-size:11.0pt; font-family:"Calibri","sans-serif";} a:link, span.MsoHyperlink {mso-style-priority:99; color:blue; text-decoration:underline;} a:visited, span.MsoHyperlinkFollowed {mso-style-priority:99; color:purple; text-decoration:underline;} span.E-MailFormatvorlage17 {mso-style-type:personal-compose; font-family:"Calibri","sans-serif"; color:windowtext;} .MsoChpDefault {mso-style-type:export-only;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 2.0cm 70.85pt;} div.Section1 {page:Section1;} --> </style> <!--[if gte mso 9]><xml> <o:shapedefaults v:ext="edit" spidmax="1026" /> </xml><![endif]--><!--[if gte mso 9]><xml> <o:shapelayout v:ext="edit"> <o:idmap v:ext="edit" data="1" /> </o:shapelayout></xml><![endif]--> <div lang="DE" link="blue" vlink="purple"> <div class="Section1"><p class="MsoNormal"><span lang="EN-US">Hi Joe,<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-US">the changed lettering for the PREAMP/ATT function<b> </b>is<b> </b>a little bit<b> </b>confusing for me: A pad in the signal path between ant and rx will reduce the signal strength and should be indicated. MDS will be reduced by the same amount. This can be watched on the meter as well on the panadapter. But with a signal at the ant plug actually I can’t watch a difference on the meter. I assume the software emulates more a proper preamp- function, indicating the signal value at the antenna plug. BTW Gerd’s mercury_eu is using a 12 dB pad instead of the 20 dB one, so things get more confused. <o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-US">May be there other reasons to provide things so?<o:p></o:p></span></p><p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p><p class="MsoNormal"><span lang="EN-US">73 Helmut, DC6NY<o:p></o:p></span></p><p class="MsoNormal"><o:p> </o:p></p> </div> </div></blockquote></div><br></body></html>