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At 23.37 14/01/2007, N4HY wrote:<br>
<blockquote type=cite class=cite cite="">It really is time to build
hardware. </blockquote><br>
So I did, spending three months to optimize it.<br><br>
<blockquote type=cite class=cite cite="">WARNING: We definitely
want to steer away from the FST switches. FROM MEASUREMENT,
coupled with DDS issues, they are the source of the increasing
noise figure. Marco's plots, as well as Phil C's and my
measurements of various QSD's using them show this inescapable
fact. I think various pieces of analysis have incorrectly
attributed the measurements but the switches are a major
contributor. <br>
They solved an early problem and we can thank Gerald for finding this
part and his very gracious publication in QEX and with the
SDR-1000. <br>
But it is time to leave them behind FOREVER.<br><br>
73's<br>
Bob<br>
N4HY</blockquote><br>
Bob, <br><br>
why do you say so? I think I measured and demonstrated exactly the
opposite: the switching noise from the FST may be minimized, and the
overall level plan of the receiver has to be considered to reduce the
noise contribution of the opamps. I see no "inexcapable facts".
<br>
Please consider the figures that I measured - in some point perhaps by
defect, see
<a href="http://www.spin-it.com/sdr/IK1ODO_SDR1.html" eudora="autourl">
http://www.spin-it.com/sdr/IK1ODO_SDR1.html<br><br>
</a><font face="Georgia" color="#4700B8">Low gain audio interface setting
(+4dBu f.s.)</font> <br><br>
<font face="Georgia" color="#4700B8">RF input level for A/D converter
saturation: -3dBm</font> <br>
<font face="Georgia" color="#4700B8">SFDR: 90dB with -10dBm RF
input</font> <br>
<font face="Georgia" color="#4700B8">Noise floor: -123dBm / 2.4kHz</font>
<br>
<font face="Georgia" color="#4700B8">3' order dynamic range: 105
dB</font> <br>
<font face="Georgia" color="#4700B8">IIP3: +36dBm</font> <br>
<br><br>
<font face="Georgia" color="#4700B8">High gain audio interface setting
(-10dBu f.s.)</font> <br><br>
<font face="Georgia" color="#4700B8">RF input level for A/D converter
saturation: -17dBm</font> <br>
<font face="Georgia" color="#4700B8">SFDR: 100dB with -20dBm RF
input</font> <br>
<font face="Georgia" color="#4700B8">Noise floor: -128dBm / 2.4kHz</font>
<br>
<font face="Georgia" color="#4700B8">3' order dynamic range: 102
dB</font> <br>
<font face="Georgia" color="#4700B8">IIP3: +25dBm</font> <br><br>
How many receivers designs get similar figures with such a simple
hardware?<br><br>
I think it's time to go ahead with Phoenix. It will not be the definitive
receiver, but using the ideas of Ahti and my tested frontend we may get a
very nice intermediate solution, at a low cost. The LO may be derived
from I0CG design (AD9951 plus a 500MHz clock); possibly a PLL in 10kHz
(or wider) steps may be better, but it's not trivial to design it with
sufficient spectral purity.<br><br>
73 - Marco IK1ODO<br>
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