Network Analysers: The Electrical Kind

Instrumentation has progressed by leaps and bounds in the last few years, however, the fundamental analysis techniques that are the foundation of modern-day equipment remain the same. A network analyzer is an instrument that allows us to characterize RF networks such as filters, mixers, antennas and even new materials for microwave electronics such as ceramic capacitors and resonators in the gigahertz range. In this write-up, I discuss network analyzers in brief and how the DIY movement has helped bring down the cost of such devices. I will also share some existing projects that may help you build your own along with some use cases where a network analyzer may be employed. Let’s dive right in.

Network Analysis Fundamentals

As a conceptual model, think of light hitting a lens and most of it going through but part of it getting reflected back.

The same applies to an electrical/RF network where the RF energy that is launched into the device may be attenuated a bit, transmitted to an extent and some of it reflected back. This analysis gives us an attenuation coefficient and a reflection coefficient which explains the behavior of the device under test (DUT).

Of course, this may not be enough and we may also require information about the phase relationship between the signals. Such instruments are termed Vector Network Analysers and are helpful in measuring the scattering parameters or S-Parameters of a DUT.

The scattering matrix links the incident waves a1, a2 to the outgoing waves b1, b2 according to the following linear equation: \begin{bmatrix} b_1 \\ b_2 \end{bmatrix} = \begin{bmatrix} S_{11} & S_{12} \\ S_{21} & S_{22} \end{bmatrix} * \begin{bmatrix} a_1 \\ a_2 \end{bmatrix} .

The equation shows that the S-parameters are expressed as the matrix S, where and denote the output and input port numbers of the DUT.

This completely characterizes a network for attenuation, reflection as well as insertion loss. S-Parameters are explained more in details in Electromagnetic Field Theory and Transmission Line Theory but suffice to say that these measurements will be used to deduce the properties of the DUT and generate a mathematical model for the same.

General Architecture

As mentioned previously, a simple network analyzer would be a signal generator connected and a spectrum analyzer combined to work together. The signal generator would be configured to output a signal of a known frequency and the spectrum analyzer would be used to detect the signal at the other end. Then the frequency would be changed to another and the process repeats such that the system sweeps a range of frequencies and the output can be tabulated or plotted on a graph. In order to get reflected power, a microwave component such as a magic-T or directional couplers, however, all of this is usually inbuilt into modern-day VNAs.
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Hackaday Links: September 3, 2017

The TI-83, TI-84, and TI-86 have been the standard graphing calculators in classrooms for two decades. This is the subject of an xkcd. Now, hopefully, there’s a contender for the throne. Numworks is a graphing calculator that looks like it was designed in at least 2006 (so very modern), and apparently, there’s a huge community behind it.

Juicero is shutting down. No one could have seen this one coming. The Juicero was a $700 press that turned proprietary, DRM’ed juice packs into juice and garbage. It was exquisitely engineered, but it turns out very few people want to spend thousands of dollars per year on DRM’ed juice. Oh, since the Juicero phones home, those $700 presses probably won’t work in the future.

Are you in the Bay area? Do you need test equipment? There’s a gigantic auction happening somewhere around San Jose. [Dave] tipped everyone off to this one, and this auction is pretty freakin’ spectacular. Spectrum analyzers, signal gens, a ‘mega zoom’ oscilloscope, and 4-channel, 500 MHz scopes for $50. There are a thousand lots in this auction. It’s nuts.

Everybody loves PCB art, and [Uri] has a guide for designing custom, functional electronic circuit boards. The toolchain used in this guide is Inkscape and KiCad, with blinky hearts, blinky pandas, and other blinky PCBs.

This one is a little out there even for us. Here’s how you build your own AA batteries. It’s a dozen #10 copper washers, a dozen or so #10 zinc washers, some cardboard, vinegar, salt, and some heat shrink tubing. The assembly of this battery is exactly what you would expect, and yes, it does work. Here’s the thing, though: The very crude tests suggest these batteries have a capacity of about 800-1000 mAh, which is far more than we would expect. Who has a programmable load and wants to do a few experiments? Also, these batteries are ‘rechargeable’ by taking them apart, sanding the crud off each washer, and adding new electrolyte.

[Jan] has made a name for himself stuffing synthesizers into tiny little microcontrollers. The latest project is the Infinity37, a polyphonic synth with MIDI, envelopes, and a whole bunch of cool stuff. Check out the video.

[rctestflight] is building a solar powered aircraft. It’s has a beautiful wing studded with solar panels. The latest flight was four hours, long enough to make piloting a plane through some FatSharks extremely tedious. Future developments will probably include a MPPT charging solution, and probably an autopilot.

Measuring Capacitors at the Birth of Rock and Roll

The late 1950s [Bill Haley], [Elvis Presley], and [Little Richard] were building a new kind of music. Meanwhile, electronic hobbyists were building their own gear from Heathkit. A lot of that gear shows you how far we’ve come in less than a century. [Jeff Tranter’s] YouTube channel is a great way to look at a lot of old Heathkit gear, including this really interesting “direct reading capacity meter.” You can see the video, below.

Measuring capacitance these days is easy. Many digital multimeters have that function. However, those didn’t exist in the 1950s–at least, not in the way we know them. The CM-1 weighed 5 pounds, had several tubes, and cost what would equate to $250 in today’s prices. Unlike other instruments of the day, though, the capacitance was read directly off a large analog meter (hence, the name). You didn’t have to interpret readings using a nomograph or move a knob to balance a bridge and read the knob’s position.

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Review: The O-scope Mayer D4/WG5 Calibrated Fleshy Test Probe

A selection of probes, from [Jim Williams'] Linear Technology app note 72.
A selection of probes, from [Jim Williams’] Linear Technology app note 72.
It’s not often that we are shown an entirely new class of test equipment here at Hackaday, so it was with some surprise that we recently received the new O-scope Mayer offering. If your most simple piece of test equipment is your own finger, able to measure temperature, detect voltage, and inject a 50 or 60 Hz sine wave, then what they have done is produce a synthetic analogue with a calibrated reading. The idea is that where previously you could only say “Too hot!”, or “High voltage!”, you should now be able to use their calibrated probe to gain an accurate reading.

The O-scope Mayer D4/WG5 Calibrated Fleshy Test Probe is a roughly 4″ (100mm) long cylinder of their InteliMeat™ synthetic finger analogue terminated with a calibrated matching unit and a BNC socket. In the box aside from the instruction leaflet is a BNC lead through which you can connect it to your oscilloscope.

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Review: Digilent Analog Discovery 2

I recently opened the mailbox to find a little device about the size of White Castle burger. It was an “Analog Discovery 2” from Digilent. It is hard to categorize exactly what it is. On the face of it, it is a USB scope and logic analyzer. But it is also a waveform generator, a DC power supply, a pattern generator, and a network analyzer.

I’ve looked at devices like this before. Some are better than others, but usually all the pieces don’t work well at the same time. That is, you can use the scope or you can use the signal generator. The ones based on microcontrollers often get worse as you add channels even. The Analog Discovery 2 is built around an FPGA which, if done right, should get around many of the problems associated with other small instrumentation devices.

I’d read good things about the Discovery 2, so I was anxious to put it through its paces. I will say it is an impressive piece of gear. There are a few things that I was less happy with, though, and I’ll try to give you a fair read on what I found both good and bad.

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Ask Hackaday: Help Me Choose A ‘Scope

If there is one instrument that makes an electronic engineer’s bench, it is the oscilloscope. The ability to track voltages in the time domain and measure their period and amplitude is one akin to a light in the darkness, it turns a mere tinkerer with circuits into one in command of them. Straightforward add-on circuits can transform a basic oscilloscope into a curve tracer, frequency response display, and much more, and modern oscilloscopes offer a dizzying array of useful measurement features unimaginable to engineers only a few years ago. And I need your help to pick a new one.

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Tools of the Trade – Test and Programming

In our final installment of Tools of the Trade (with respect to circuit board assembly), we’ll look at how the circuit board is tested and programmed. At this point in the process, the board has been fully assembled with both through hole and surface mount components, and it needs to be verified before shipping or putting it inside an enclosure. We may have already handled some of the verification step in an earlier episode on inspection of the board, but this step is testing the final PCB. Depending on scale, budget, and complexity, there are all kinds of ways to skin this cat.

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