Review: Signal Hound BB60C real time 6 GHz spectrum analyzer - Part 2
One of the first things I tried was to measure the near field emissions of my ST Microelectronics STM32-F4 “Discovery” embedded controller. This is an evaluation board with STM32F-series microcontroller, built-in 2.4-inch TFT display and 64 MB of SDRAM. The primary clock frequency is 8 MHz, which gets unconverted to the 180 MHz processor clock.
Figure 5 - Measuring the near field emissions of the STM32-F4 embedded controller using a Beehive Electronics H-field probe.
As a quick check, I’ll compare the spectral profile of this board between my Rigol DSA815 and the Signal Hound BB60C. I scanned around with the probe to find the largest average emission profile and then left it there during the comparison measurements.
Figure 6 - The emission profile of the STM32-F4 Controller as measured with the Rigol DSA815.
Figure 7 - The emission profile of the STM32-F4 Controller as measured with the Signal Hound BB60C.
As you can see, comparing Figures 6 and 7, we get virtually the same spectral profile. The major harmonic peak is at 270 MHz. With persistence turned on, the Signal Hound reveals a lot more activity around the central portion of the frequency scan. In fact, there was a periodic signal sweeping slowly from right to left (blue-colored trace), that was difficult to detect using the Rigol. In Figure 8, I managed to freeze part of that sweeping signal, which shows up as a downward notch in the emission (circled).
Figure 8 - The sweeping signal was captured as it slowly moved from right to left using the BB60C analyzer (circled). I believe it had something to do with the TFT display sync signal.
This notch would gradually move across the displayed frequency plot and was virtually invisible on the Rigol analyzer.
The BB60C also has the capability to display 2D and 3D waterfall plots. Figures 9 and 10 show this. If you look carefully, you can see the sweeping notch, which appears as faint diagonal lines in the waterfall.
Figure 9 - The same frequency plot as in Figures 7 and 8 above, but showing the 2D waterfall display.
Figure 10 - The same frequency plot, but showing the 3D display. You can grab the display with the mouse and move it around for the best view.
In the next experiment, we’ll take a look at the FM broadcast band. I connected short telescoping whip antenna. Figure 11 (same as Figure 5 in Part 1) shows most of the FM band. What I found interesting was a series of closely-spaced pulsed harmonics. These appear to be coming from the switching power supply on my nearby iMac computer and were simply not visible on the Rigol DSA815 analyzer.
Figure 11 - The FM broadcast band as received using an outdoor antenna. Note the series of pulsed harmonics (in blue-green).