Theory of Operation |
Limitations of the Signal Hound
7
amplitude with no signal present (the noise), in linear power units, from the amplitude with signal
present, to calculate the signal level. Please note that the measurement uncertainty will increase from
this process.
3
Theory of Operation
Learn about the internal blocks that make up the Signal Hound
The Signal Hound is built around a narrow-band IF-to-bits receiver with a maximum bandwidth of 250
KHz. It receives up to 2 Megabytes of I/Q data each second, which it processes into a trace. To bring you
a low cost, compact spectrum analyzer, we used high-level RF integrated circuits. The block diagram,
below, illustrates the major elements of the design. Image rejection is accomplished by mixing high side
and low side (sometimes with separate IF frequencies), then masking together the results.
Figure 5: Simplified Block Diagram
3.1.1
Operating Modes
I/Q streaming: This is used for real-time mode (frequency domain) and zero span mode
(time domain). In this mode, the USB-SA44B continuously mixes a fixed LO frequency with
the RF input and streams the data to the PC or laptop for processing.
Narrowband Sweep: This mode is used for spans of 200 kHz or less. In this mode, a fixed,
predetermined amount of I/Q data is captured at two distinct combinations of LO and IF
frequencies, then combined into a single trace for display. There are minimal restrictions
on RBW.
Midrange Sweep: For spans of 201 kHz to 99 MHz with a start frequency above 16 MHz, the
firmware captures between 256 and 65,536 I/Q samples at each 200 kHz step, allowing
RBW / VBW settings of 30 Hz to 250 kHz.
Wide Sweep: For all other spans, the firmware captures 256 I/Q samples at each 200 kHz
step, meaning RBW and VBW must be 6.5 kHz or higher.
Broadband Sweep: 5 MHz RBW, only available above 200 MHz start frequency. Rapidly
sweeps across the spectrum, to find a strong signal quickly. Certain RF frequencies may
produce spurious responses in this mode, and amplitude accuracy is reduced.