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<DIV><SPAN class=029193320-19122006>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">The detector integrates the fraction
of the RF pulse onto the detection cap.<SPAN style="mso-spacerun: yes">
</SPAN>Physically, this integration is done using the R/C low pass filter effect
of R, the system impedance, and C which is the detection cap.<SPAN
style="mso-spacerun: yes"> </SPAN>The loss appears across the system
impedance and is not visible at the input to the detector since the voltage drop
across the system impedance has already happened. By selecting C we affect
the roll off of the R/C low pass filter and thus C is relative small for an SDR
front end (0.01 uf – <SPAN class=029193320-19122006>small RC time constant
= </SPAN>wide<SPAN class=029193320-19122006>r</SPAN> bandwidth<SPAN
class=029193320-19122006>, 10's of KHz wide</SPAN>), and relatively large (0.82
uf – <SPAN class=029193320-19122006>larger R/C time constant =
</SPAN>narrow<SPAN class=029193320-19122006>er </SPAN>band<SPAN
class=029193320-19122006>width; ~1 KHz wide</SPAN>) for a <SPAN
class=029193320-19122006>traditional analog </SPAN><SPAN
class=029193320-19122006>DC phasing </SPAN>receiver such as the
NC2030.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office"
/><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Integrating 180 degrees of the RF
waveform onto each of two detection caps mathematically gives square
root of 2 times the peak or 0.707x the voltage, a 3 db detection loss.<SPAN
style="mso-spacerun: yes"> </SPAN>Evaluating the integration of a sine
wave from 0 to 180 degrees is a straightforward mathematical exercise. On
the other hand, integrating over 90 degrees of the RF waveform on to each of
four detection caps gives 0.9x the peak RF voltage, a 1 db loss. This is
the same as evaluating the integration of a sine wave from 45 to 135 degrees,
integration over the 90 degree section of a sine wave that covers the peak.
Thus, these losses do have a mathematical basis.<SPAN
style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">The fact that folks look at the
input to the detector and see that 1v pk-pk RF waveform into the detector gives
1v pk-pk of detected base band audio are missing the fact that voltage drop
(loss) that has already happen across the 50 ohm system impedance before the
detector input<SPAN class=029193320-19122006>.</SPAN><SPAN
class=029193320-19122006> Thus it is easy to come to the conclusion that the
detector has basically no conversion loss and is thus more of a "sample and
hold" type process rather than an integrating process.</SPAN></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">- Dan,
N7VE</SPAN></SPAN></P></DIV></BODY></HTML>