This review is condensed from a full FPC1500 review at element14, click here.
There is also a video here:
During my time using it, although it is a very new product, I found no bugs that I could not work around. The bugs were very slight, and have been reported so the next firmware update should be even better. The unit is light, compact, and totally silent because there is no fan. More than any other instrument, RF tools in general
need to be powered up for hours while tweaking designs, so I was impressed that I no longer have to live with loud equipment noise right next to me. For me this is a huge productivity boost alone. The screen is really large, and clear provided it is viewed face-on.
The supplied PC software, called InstrumentView, is excellent. The Get Trace feature inside it is extremely good. It captures deep information that can be annotated with markers and overlaid with subsequent traces, but it also captures all the information that typically one would forget to write down if just a screen capture had been obtained, such as whether any parameters were manually set,
what averaging and detector was applied, and so on. The dataset that is captured could be given to anyone else running InstrumentView, so they can see all this detailed information too.
Spectrum Analyzer Performance
The noise floor is really low. Also, the FPC1500 has a resolution bandwidth down to 1Hz so this helps to have a low noise floor on the screen.
Another parameter is the range of possible input power that can be viewed. The FPC1500 has a clear 10dB at the top end compared to other similar priced spectrum analyzers, and a massive difference at the bottom too, depending on which spectrum analyzer it is compared against.
Using H-Field and E-Field Probes
A great use-case for spectrum analyzers is to examine a circuit for EMI or electromagnetic interference, or just to see what is going on in the circuit using a non-intrusive method.
A couple of ways are to use magnetic and electric field probes, also known as H-Field and E-field probes.
The FPC1500 is sensitive enough to work very well with even small probes. I applied the probe to areas close to the inductors on the Pi 3 model B. It was interesting to see the change in activity as the CPU load was increased. When all four cores were busy, the activity increased. Ordinarily you might not know the precise frequency span of interest, so it is good that the FPC1500 is quite speedy even with large spans, and yet has a great noise floor too. It makes it really handy for such probing activity quickly around a PCB with a small probe.
A nice feature of the FPC1500 is the built-in signal generation capability. It can be used independently, or tied to the spectrum sweep. As an example, I used it to examine the response of a homemade amplifier, and it worked as expected. This is a normal use of a tracking generator and even without it there are workarounds
using an external signal generator, however where the capability comes into its own is combined with the vector network analyzer (VNA) capability that will be described very shortly.
Measuring Phase Noise of Oscillators
Armed with the tracking generator capability and a few other nice features of the FPC1500, it is feasible to measure the phase noise of external oscillators.
To do this, one method is to measure the phase noise at a frequency which matches a crystal filter.
With the tracking generator, it is possible to see the filter response and see the difference between the passband area, and the filtered area.
Now the tracking generator can be switched off, and the oscillator was connected to the filter instead.
I set the oscillator frequency to sit outside of the filter passband, and then I would measure the phase noise inside the passband. This way the oscillator fundamental will only appear as a small peak that is will within the spectrum analyzer dynamic range, meaning that there is no risk of the spectrum analyzer’s own oscillator
phase noise being visible on the screen. With a very low noise floor and possible preamplifier enabled, it should be possible to observe the phase noise of the oscillator within the passband because that will not be attenuated greatly at all.
I set the marker to noise mode, where it automatically makes all the correct calculations and displays the phase noise. Now this value is relative to the carrier it sees, because it has no idea there is a filter attached. So all that needs
to be done is to subtract the filter passband difference, and all is complete.
This is a difficult measurement to achieve without a very high-end spectrum analyzer, but the FPC1500 with Preamplifier, Tracking Generator, and Noise Marker makes it possible!
The reason for the calibration is that the VNA works by measuring the phase of reflections from whatever is connected to it. It is also known as a S11 or one-port measurement, and it is extremely useful. To save headache there is the ZN-Z103 which is an electronic calibration tool. One end of it has a USB connection to the FPC1500, so that it can be controlled by it during the one-touch calibration procedure. After calibration you can hook up an antenna or any other device under test, taking a lot of care not to move any cables or loosening any connectors
Another great feature of the FPC1500 is the in-built application that makes use of the VNA to perform cable measurements. There are a couple of features actually, but the one I tested shows any faults or anomalies over the length of a cable. It works even when only one end of the cable can be connected to the device.
The way it works is that it sends various frequencies into the cable, and examines the phase of the reflection. In the time domain this corresponds to delay, which of course is related to length. This means that it is possible to have an x-axis marked in metres, so you can see at what point on the cable anomalies are present. There are dozens of cable models pre-loaded into the FPC1500, and more can be
created using the supplied InstrumentView software.
I felt that this instrument is really suited for very diverse use-cases. The VNA opens up a lot of opportunities for cable and component testing and characterisation, as well as the very important task of antenna matching. This instrument never felt like a cut-down device. The performance and features mix
is excellent, and any engineer will get a lot done with this on the workbench.
If I could change just one thing, it would be better viewing angles on the display. This is a fantastic instrument otherwise – very stable software, nice construction and what great features!
For the full review, see element14.