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<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial>Scott,</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>This
is counter-intuitive to me. I suspect this is wrong, sorry. So, I
took my Wavetek attenuator and hooked it to the rx input on the Hermes, 20M
ssb.</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>As the
DAT31 is right there before any amplification, the Wavetek is doing the same
job.</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>With
the S-ATT set at zero, as I increase the input attenuation (Wavetek), only the
signal decreases. Of course, part of the noise floor is band noise, so
some</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial>lowering of the ultimate noise floor was </FONT></SPAN><SPAN
class=866021112-06052015><FONT color=#0000ff size=2
face=Arial>shown.</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>The
external Wavetek works exactly as I suspected the internal DAT31 should, only
decrease the incoming signal (plus noise).</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>I am
concluding that there is some problem with my Hermes.</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>When I
tune to an unused portion of the band, the noise floor shows -117db. As I
increase the attenuation to 30db and beyond, the bottom reaches -120 no
more.</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial>73's</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2 face=Arial>Glen
K4KV</FONT></SPAN></DIV>
<DIV><SPAN class=866021112-06052015></SPAN> </DIV>
<DIV><SPAN class=866021112-06052015><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<BLOCKQUOTE style="MARGIN-RIGHT: 0px" dir=ltr>
<DIV dir=ltr class=OutlookMessageHeader align=left><FONT size=2
face=Tahoma>-----Original Message-----<BR><B>From:</B> Hpsdr
[mailto:hpsdr-bounces@lists.openhpsdr.org]<B>On Behalf Of </B>Scott
Traurig<BR><B>Sent:</B> Tuesday, May 05, 2015 10:45 PM<BR><B>To:</B> Glenn
Elmore<BR><B>Cc:</B> hpsdr<BR><B>Subject:</B> Re: [hpsdr] Hermes now
rxing<BR><BR></FONT></DIV>
<DIV dir=ltr>Perhaps it is more important to realize that the step attenuator
is in front of the first receiver amplifier. Because of that the receiver
noise figure is going to be increased (worsened) by the amount of step
attenuation selected.
<DIV><BR></DIV>
<DIV>73,</DIV>
<DIV><BR></DIV>
<DIV>Scott/w-u-2-o</DIV>
<DIV><BR></DIV></DIV>
<DIV class=gmail_extra><BR>
<DIV class=gmail_quote>On Tue, May 5, 2015 at 6:44 PM, Glenn Elmore <SPAN
dir=ltr><<A href="mailto:n6gn@sonic.net"
target=_blank>n6gn@sonic.net</A>></SPAN> wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>***** High Performance Software Defined Radio Discussion
List *****<BR><BR><BR>I would say this is both normal and the desired
behavior. It's what a commercial spectrum analyzer does. The reported level
is referenced to the antenna/input connector. What happens inside the
receiver, other than the resolution/display bandwidth, shouldn't affect
this.�� When internal attenuation or preamplification is added or removed,
the receiver fixes the reporting to make those changes invisible. The
exception to this is that the displayed S Meter reading is reporting the
total power within the selected bandwidth. If it's mostly a carrier with
high S/N then you get the carrier's level. If it is mostly/all noise then
you get the noise power in that bandwidth.�� Attenuation or preamplification
within the receiver just changes the sensitivity (noise figure) but
doesn't/shouldn't change what is coming in or how it is reported.<BR>Having
the reporting done this way not only removes the receiver from the
measurement but lets one calculate, for example, system noise figure by
subtracting 10*log(bw) from the displayed reading on noise and comparing it
with KTB in 1 Hz - -174 dBm.�� This is useful in comparing QRN levels to a
"quiet" world on HF (which I never see any more!)<BR><BR>Glenn n6gn<BR><BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>The noise floor with the S-ATT at zero is very low,
probably around -135db<BR>on 20M right now.�� As I raise the S-ATT the
noise<BR>floor rises to -110db and the signals disappear.�� I would have
thought just<BR>the signals would decrease as I raised the
S-ATT!?<BR><BR>Is this normal
behavior?<BR><BR></BLOCKQUOTE>*****************************<BR>_______________________________________________<BR>HPSDR
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