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<DIV
style='FONT-SIZE: small; TEXT-DECORATION: none; FONT-FAMILY: "Calibri"; FONT-WEIGHT: normal; COLOR: #000000; FONT-STYLE: normal; DISPLAY: inline'>I
agree with Helmut on this. The ADC inputs of the RP were designed for
using with scope probes, and have a high input impedance. Even with your
Norton amp in front, and the splitter, there is probably some loss due to this
situation. Also, don’t forget that you are looking at a 14-bit ADC (and
generic design) vs the QS1R SDR-specific (50 ohm) input circuitry. I don’t
remember offhand which “preamp” chip the QS1R uses in front of the ADC, but I
believe Phil Covington did a better SDR design than the RP has. So, its
probably a little more sensitive. IIRC the RP uses the LTC 6400, or
6405. The QS1R SHOULD handily win any direct comparisons on receive.
At least unless you plan to use it/them for either a complete transceiver, or
for diversity! Also, the cost comparison is a winner for the RP!</DIV>
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<DIV>I’m looking at an active preamp and Brainerd BPF in front of the RP, to
help it out some on HF. For LF, it’s probably not going to cut it.
Initial tests about a year ago showed some trash on 470kHz, and way too much
garbage at 137kHz.</DIV>
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<DIV>Still, the RP is a VERY interesting board to play with for around
$250. I’ve bought two now, and am looking at a third. One will be to
play with the bench test equipment stuff for it, and the others will be for SDR
purposes.</DIV>
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<DIV>I’m taking my wife to various doctors after a bad fall and some broken
bones, so my time is rather limited at the moment. But, I’ll let you know
how my tests go as I get them done. I DO plan to test under at least
HDSDR, SDR#, GNU Radio, and PowerSDR, to be sure there aren’t many
differences.</DIV>
<DIV>73, Terry, N4TLF</DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=dc6ny@gmx.de>Helmut</A>
</DIV>
<DIV><B>Sent:</B> Wednesday, October 26, 2016 4:50 PM</DIV>
<DIV><B>To:</B> <A title=n4zr@comcast.net>'Pete Smith N4ZR'</A> ; <A
title=hpsdr@openhpsdr.org>hpsdr@openhpsdr.org</A> </DIV>
<DIV><B>Subject:</B> Re: [hpsdr] A real newbie question</DIV></DIV></DIV>
<DIV> </DIV></DIV>
<DIV
style='FONT-SIZE: small; TEXT-DECORATION: none; FONT-FAMILY: "Calibri"; FONT-WEIGHT: normal; COLOR: #000000; FONT-STYLE: normal; DISPLAY: inline'>*****
High Performance Software Defined Radio Discussion List *****<BR><BR>
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<P class=MsoNormal><SPAN
style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'>Pete,<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'><o:p></o:p></SPAN> </P>
<P class=MsoNormal><SPAN lang=EN-US
style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'>I
guess you know that some modifications of the frontend are necessary to use the
RP as an appropriate SDR. Impedance transformation from high to 50 ohms seems
helpful as well as sufficient low-pass filtering for the 1. Nyquist zone. The
preamp for frequencies > 7 MHz needs a redesign. When you have done this work
calibration can be taken as Warren has described. To get best accuracy a high
reference (signal source) level should be used to employ as much bits of the ADC
as possible (just below clipping).<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US
style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'><o:p></o:p></SPAN> </P>
<P class=MsoNormal><SPAN lang=EN-US
style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'>73,
Helmut, DC6NY</SPAN></P>
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style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'></SPAN> </P>
<P class=MsoNormal><SPAN lang=EN-US
style='FONT-SIZE: 11pt; FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d'>cut
to reduce
size....N4TLF<o:p></o:p></SPAN></P></DIV></DIV></DIV></DIV></DIV></DIV></DIV></BODY></HTML>