Special Project: Receive a Spectrum Analyzer and Demonstrate EMI debugging, low power design, or IoT Application

Could this special project be a design challange a project14 competition or just a Roadtest?

Some good online resources/documentation will really help. Also. some Bluetooth Low Energy test antenas or kits would be nice to have for the last two tasks in bullet points.

If there is a selection between spectrum analysers ofered by R&S that would also be nice.

Since we can propose different applications, I propose to design two RF bandpass filters. My plan is to build an Automatic Identification System (AIS) 162 MHz lumped element filter and an Automatic Dependent Surveillance–Broadcast (ADS-B) 1090 Mhz lumped element filter. I will use free tools such as QUCS to design the filter, but eventually use trials of more advanced tools such as Keysight’s Genesys (this will depend on if they approve my trial requests). The aims of the design will be towards minimal attenuation of the passband, maximal attenuation outside the passband, and robustness against imperfections of the PCB manufacturing process and component variability. The designs will be manufactured at the inexpensive PCB manufacturer JLCPCB.

With the filters in hand, I will measure the S21 parameter curves of the filters and evaluate how well they match the curves computed by software and how similar they are between each other (due to component and fabrication variability). Finally, I will test the filters with the SDR to see how well they perform.

Besides the associated software VNA options I would need a 2-port calibrator. It also would be nice a pair of cables, as I would not like to mate my unbranded connectors to the VNA and calibrator out of fear of damaging their connectors.

I would be really interested in a webinar/virtual classroom.

Do you have any (better) ideas on how to do this special project? Please leave a comment.

At this point, I am still brainstorming on how I will do this special project. R&S is very interested. Any other feedback you can provide is welcome.

I'm sure there are a lot of people who are comfortable with electronics in general and happy with using an oscilloscope, but don't tend to delve too deeply into RF and may not immediately be able to get the most out of a spectrum analyzer or the more advanced features of a device like the FPC1500.

The FPC-Z10FPC-Z10 Teaching Kit is an interesting companion for the FPC1500. There is a good user guide for both devices, but it seems you need to read both side-by-side and cross reference them to get the most out of finding your way around. Perhaps the FPC-Z10 is aimed at a teacher-led classroom rather than self paced study. I wonder if there would be demand for a webinar based around these devices? I'm sure there would be interest. I suppose the big question is how many people would make use of a webinar where the prerequisite is a couple of pieces of expensive test equipment. What does eveyone else think?

makes me think of an antenna project I did back in 2015: Old meets new, the 1-Wire Weather Station on the SPARK Core. (part 7)

Did not do any measures on it by then, would be great to put the FPC1500 VNA in action for this.

Project Proposal

My proposal is to focus on the VNA features of the FPC1500 for IoT antenna matching. I am by no means an RF expert - although I'd love to learn more. However, this is an area I am familiar with.

I've created a number of different custom NFC antenna designs - one using a wirewound inductor and another a very small PCB antenna. These were intended to work well with a tiny implanted NFC tag. Due to the small size of the tag, getting the most from the reader antenna and maximizing the limited range range was critical.

As I didn't have access to a Vector Network Analyzer, I've had to perform the antenna matching without one. I've blogged here about techniques for doing this and they were ultmately successful, but it would be great to compare this with the same process using the right tool for the job!

NFC antenna tuning without a VNA

In another project I needed to read a tag in a ball with unknown orientation. Due to the very directional nature of NFC, I created a prototype using a multiplexed antenna array - with multiple antennas connected through a RF switch. It will be interesting not just to see how a VNA helps tune the individual antenna characteristics, but also how these characteristics present themselves when measured through the RF switch. (This NFC prototype worked but was ultimately rejected in favour of a 2.4GHz BLE solution - once again with a small 50 ohm custom PCB antenna.)

I'd also like to use the spectrum analyzer and tracking generator to visualize how the coupling between reader and tag varies with orientation. This might initially seem like a perfect fit for one of the HZ-17 H-field probes, but they're designed to work with a higher frequency range and are a bit overqualified for the job!

Equipment required

The main item required for this project would be the FCP-COM2FCP-COM2. This bundle of the FPC1500 with hardware and software options is incredibly good value, so you'd be crazy to pick anything else!

The only other thing needed for good S11 measurements is a way of ensuring good calibration of the device alongside you cables. The easiest way is definitely to use the ZN-Z103ZN-Z103 which is a simple repeatable one-click solution for 1-port calibration. However, there's also the FPC-Z10FPC-Z10. This is intended to be a teaching aid for the FPC1500 but it does include open, short and through loads. Sure there's more manual work involved in calibration, but there's also the chance to get a better feel for your test equipment and it could be an interesting alternative.

R&SFPC1500, what a wonderful test instrument . For sure, I would be interested in demonstrating its features, especially the ones useful in IoT applications.

My proposal would be to follow the above linked R&SFPC Application Notes, but I would also mix it up with some content targeted more towards DIY Projects / Applications:

Antenna & RF Port Impedance Verification & Matching

I think the most useful feature of a Spectrum Analyzer (with or without Vector Network Analyzer) for DIY projects is the ability to verify and tune Antennas to match a required impedance (usually 50Ω). The FPC1500 not only includes a Vector Network Analyzer but also has a built-in VSWR bridge, which allows us to test Antennas and other RF devices without the need for additional accessories.

I would really like to demonstrate Reflection Coefficient (Γ), Voltage Standing Wave Ratio (VSWR) and Return Loss (RL) measurements, and as will as Smith chart measurements with the R&SFPC1500.

The Devices Under Test (DUT) would include a wide variety of Antennas and other RF Devices:

• a wide variety of Antennas with different Frequency ranges (433 / 868 MHz, 2.45 / 5 GHz, GSM, etc.)
• PCB / Chip Antennas (2.45 GHz)
• NFC Antennas (13.56 MHz)
• Ettus USRP B205mini-i Software Defined Radio
• HackRF One Software Defined Radio
• N1201SA+ Antenna Analyzer

Gear:

• R&SFPC1500 Spectrum Analyzer (R&SFPC1500) with 1-2 and 2-3 GHz upgrades (R&SFPC-B2, R&SFPC-B3)
• 2MHz to 4 GHz Calibration Unit (R&SZN-Z103)
• Vector Reflection Measurement option (R&SFPC-K42)

Resources:

• RF port impedance verification
• Antenna matching in IoT and low power devices

Bluetooth Low Energy (BLE)

The The smarter way to test BLE transmit signals application card describes some super interesting features of the R&SFPC1000/1500 that allows debugging Bluetooth Low Energy (BLE) signals. I would demonstrate these features using a wide variety of Bluetooth Low Energy (BLE) dongles, development boards and also some of my custom made BLE gadgets.

Gear:

• R&SFPC1500 Spectrum Analyzer (R&SFPC1500) with 1-2 and 2-3 GHz upgrades (R&SFPC-B2, R&SFPC-B3)
• 2MHz to 4 GHz Calibration Unit (R&SZN-Z103)
• Spectrum Analyzer Preamplifier option (R&SFPC-B22)
• Modulation Analysis option (R&SFPC-K7)

• Vector Reflection Measurement option (R&SFPC-K42)
• Receiver Mode option (R&SFPC-K43)
• Advanced Measurements option (R&SFPC-K55)
• Wi-Fi Connection Support option (R&SFPC-B200, optional)

Resources:

• The smarter way to test BLE transmit signals

EMI Testing / Debugging

I could also demonstrate EMI Testing / Debugging, but not on mains powered supplies (I'm afraid I would shock myself ), but on Low Voltage Buck / Boost Converters. These are switching mode DC-to-DC converters often running at up to 2 MHz frequencies. I use them in projects with custom PCB-s to power IC-s running at different voltages: 1.8 / 3.3 / 5.0 V. As I usually do no testing on these, beyond verifying the output voltage is correct, so it would be interesting to see how they perform from EMI point of view.

Gear:

• R&SFPC1500 Spectrum Analyzer (R&SFPC1500)

• Receiver Mode option (R&SFPC-K43)
• Probe set for H near-field emission measurements (R&SHZ-17)
• EMI emissions test software (R&SELEMI-E)
• R&SELEKTRA license dongle (R&SEMCPC)

Resources:

• EMI debugging a switched-mode power supply with R&SFPC1000/ R&SFPC1500

I am torn about whether to apply for this. I have at least a dozen antennas that work below 3 GHz that I would like to test with a VNA, but they mostly have ULF connectors.

I also have a noisy switching supply that I need to improve, but it would likely need a line impedance stabilization network (LISN) to test conducted emissions. I would like to try pre-EMC testing on some devices, but would need a transverse electromagnetic (TEM) cell and maybe some near-field probes to test for radiated emissions. I will likely pass on the contest since I don't have enough support apparatus, but at least the research into whether I should apply has provided some insight into what would be involved.

The FR4 doesn't do much except provide mechanical support.

The copper on both sides is joined together at small and regular intervals by shorting links.

The more sophisticated devices break the middle plane into long strips joined by lateral resistors - I'm not sure but I think that the two sides are still linked on each strip.

The TEKbox ready made cells look pretty good - and in the context of the price of the measuring instruments they are very cheap. The smallest is about the same price as the R & S calibrator.

I got my cheapo 25W 20dB attenuator today. According to the FPC1500 the input return loss >>20dB and the attenatuion 19.4dB +/- <0.2dB (both up to 1GHz.)

MK

Thanks for showing us your TEM cell build. It's a good advert for the practical kind of things a FPC1500 enables you to do.

I'm not always all that good with this kind of rf stuff, but within the cavity inside the pcb sheet won't the wave velocity be about a quarter of that in free space (the dielectric 'constant' for FR4 is, very roughly speaking, down to just over 4 as you move up towards a GHz)? If so, the wavelength is more like 75mm, and the quarter wave for cut-off to stop standing waves inside more like 18mm than the 50mm they've used. Or have I got that the wrong way round?