to the quantizing level or dither noise would have to be added outside the passband. Fig.\ \ref{fig:figure_6} illustrates the signal-to-noise ratio curve with external noise for the 10-m band and 40 dB of INA gain. Fig.\ \ref{fig:figure_5} shows the same curve without external noise and with INA gain of 60 dB. This much gain would not improve the sensitivity in the presence of external noise but would reduce blocking and IMD dynamic range by 20 dB. On the lower bands, 20 dB or lower INA gain is perfectly acceptable given the higher external noise.

\section{Frequency Control}
Fig.\ \ref{fig:figure_7} illustrates the Analog Devices AD9854 quadrature DDS circuitry for driving the QSD/QSE. Quadrature local-oscillator signals allow the elimination of the divide-by-four Johnson counter, described in Part 1, so that the DDS runs at the carrier frequency instead of its fourth harmonic. I have chosen to use the 200-MHz version of the part to minimize heat dissipation, and because it easily meets my frequency coverage requirements of dc--60 MHz. The DDS outputs are connected to seventh-order elliptical low-pass filters that also provide a dc reference for the high-speed comparators. The AD9854 may be controlled either through a SPI port or a parallel interface. There are timing issues in SPI mode that require special care in programming. Analog Devices have developed a protocol that allows the chip to be put into external I/O update mode to work around the serial

\begin{table}
\caption{SDR-1000 Level Analysis Detail for the 10-Meter Band with 40 dB of INA Gain}
\label{tab:table_8}
\begin{tabular}{cccccccccccc}
Antenna & INA & Antenna & Total & Sound Card & Noise at & A/D & Noise in & Quantizing & Total & Output S/N & Digital \\
Signal & Output & Overload & Analog & AGC & A/D Input & Signal & A/D Input & Noise of A/D & Noise & Ratio & Gain \\
Level & Level & Level & Gain & Reduction & in BW1 & Level & in BW2 & in BW2 & in BW2 & in BW2 & Required \\
(dBm) & (dBm) & (dBm) & (dB) & (dB) & (dBm) & (dBm) & (dBm) & (dBm) & (dBm) & (dB) & (dB) \\
-128 & -82 &  & 46.0 & 0.0 & -63.0 & -82.0 & -82.0 & -88.4 & -81.1 & -0.9 & 86.0 \\
-118 & -72 &  & 46.0 & 0.0 & -63.0 & -72.0 & -82.0 & -88.4 & -81.1 & 9.1 & 76.0 \\
-108 & -62 &  & 46.0 & 0.0 & -63.0 & -62.0 & -82.0 & -88.4 & -81.1 & 19.1 & 66.0 \\
-98 & -52 &  & 46.0 & 0.0 & -63.0 & -52.0 & -82.0 & -88.4 & -81.1 & 29.1 & 56.0 \\
-88 & -42 &  & 46.0 & 0.0 & -63.0 & -42.0 & -82.0 & -88.4 & -81.1 & 39.1 & 46.0 \\
-78 & -32 &  & 46.0 & 0.0 & -63.0 & -32.0 & -82.0 & -88.4 & -81.1 & 49.1 & 36.0 \\
-68 & -22 &  & 46.0 & 0.0 & -63.0 & -22.0 & -82.0 & -88.4 & -81.1 & 59.1 & 26.0 \\
-58 & -12 &  & 46.0 & 0.0 & -63.0 & -12.0 & -82.0 & -88.4 & -81.1 & 69.1 & 16.0 \\
-48 & -2 &  & 46.0 & -3.3 & -63.0 & -5.4 & -95.4 & -88.4 & -83.6 & 78.2 & 9.4 \\
-38 & 8 &  & 32.7 & -13.3 & -76.4 & -5.4 & -105.4 & -88.4 & -87.6 & 82.2 & 9.4 \\
-28 & 18 &  & 22.7 & -23.3 & -86.4 & -5.4 & -115.4 & -88.4 & -88.3 & 82.9 & 9.4 \\
-18 & 28 &  & 12.7 & -33.3 & -96.4 & -5.4 & -125.4 & -88.4 & -88.4 & 83.0 & 9.4 \\
-8 & 38 & 16 & 2.7 & -43.3 & -106.4 & -5.4 & -135.4 & -88.4 & -88.4 & 83.0 & 9.4 \\
2 & 48 & 26 & -7.3 & -53.3 & -116.4 & -2.0 & -142.0 & -88.4 & -88.4 & 86.4 & 6.0 \\
12 & 58 & 36 & -14.0 & -60.0 & -123.0 & 8.0 & -142.0 & -88.4 & -88.4 & 96.4 & -4.0 \\
22 & 68 & 46 & -14.0 & -60.0 & -123.0 & 18.0 & -142.0 & -88.4 & -88.4 & 106.4 & -14.0 \\
32 & 78 &  & -14.0 & -60.0 & -123.0 & 28.0 & -142.0 & -88.4 & -88.4 & 106.4 & -14.0 \\
\end{tabular}
\end{table}