Fail Of The Week: How Not To Design An RF Signal Generator

We usually reserve the honor of Fail of the Week for one of us – someone laboring at the bench who just couldn’t get it together, or perhaps someone who came perilously close to winning a Darwin Award. We generally don’t highlight commercial products in FotW, but in the case of this substandard RF signal generator, we’ll make an exception.

We suppose the fail-badge could be pinned on [electronupdate] for this one in a way; after all, he did shell out $200 for the RF Explorer signal generator, which touts coverage from 24 MHz to 6 GHz. But in true lemons-to-lemonade fashion, the video below he provides us with a thorough analysis of the unit’s performance and a teardown of the unit.

The first step is a look at the signal with a spectrum analyzer, which was not encouraging. Were the unit generating a pure sine wave as it should, we wouldn’t see the forest of spikes indicating harmonics across the band. The oscilloscope isn’t much better; the waveform is closer to a square wave than a sine. Under the hood, he found a PIC microcontroller and a MAX2870 frequency synthesizer, but a conspicuous absence of any RF filtering components, which explains how the output got so crusty. Granted, $200 is not a lot to spend compared to what a lab-grade signal generator with such a wide frequency range would cost. And sure, external filters could help. But for $200, it seems reasonable to expect at least some filtering.

We applaud [electronupdate] for taking one for the team here and providing some valuable tips on RF design dos and don’ts. We’re used to seeing him do teardowns of components, like this peek inside surface-mount inductors, but we like thoughtful reviews like this too.

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A Microwave Erector Set

RF design isn’t always easy, especially at higher frequencies. Despite improvements in simulation tools, there’s still no substitute for prototyping and trying out different things. That wasn’t so bad when that meant nailing some nails in a piece of wood and wiring up discrete components. But at today’s microwave frequencies and with today’s IC packaging that simply doesn’t work. Solving this problem is what drives a company called X-Microwave. They have a standard grid pattern PCB for a wide range of RF circuits and accessories to tie them all together. Probably the best way to get a feel for the system is to watch the simple video below. There’s also a free simulator tool worth taking note of that you’ll see in a bit.

Before you get too excited, we’ll warn you that while this stuff is cheap if you need it, it isn’t an impulse buy. The baseboards and probes (the connectors) run from $150 to $300. You can get kits, too, but a bare-bones two-port system is going to start at about $550, which is about $100 off the component parts and includes some extras. Then you need less expensive parts to make the boxes around things if you need them. Oh. Then you also need the PCBs which are not cheap, either. Their prices vary widely as you’d expect, but — for example — we saw amplifiers as low as $80 and as high as nearly $1000. So a complete system could get pretty pricey.

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Real World RF Filter Design And Construction

We bet when [devttyS0] made his latest video about RF filter design (YouTube, embedded below), he had the old saying in mind: in theory, there’s no difference between theory and practice, but in practice, there is. He starts out pointing how now modern tools will make designing and simulating any kind of filter easy, but the trick is to actually build it in real life and get the same performance. You can see the video below.

One of the culprits, of course, is we tend to design and simulate with perfect components. Wires have zero resistance, capacitance, and inductance. Inductors and capacitance have no parasitic elements in our rosy design world. Even the values of components will vary from their ideal values and may change over time.

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Hackaday Links: October 9, 2016

Atari is back! That’s what some dude says. There are no real details in that post, other than ‘Atari is Back!’

The ESP32 is coming, and it’s going to be awesome. Espressif has just released an Arduino core for the ESP32 WiFi chip. The digitalRead, digitalWrite, SPI, Serial, Wire, and WiFi “should” work. If you’re looking for ESP32 hardware, they’re infrequently available and frequently out of stock. Thankfully, stock levels won’t be the Raspberry Pi Zero all over again until someone figures out how to run an NES emulator on the ESP32.

Tiny, cheap ARM boards would make for great home servers if they had SATA or multiple network interfaces. Here’s a Kickstarter for a board with both. It’s based on an ARM A53 with multiple Ethernets, mini PCIe, enough RAM, and SATA. It’s a board for niche use cases, but those uses could be really cool.

You’re not cool or ‘with it’ until you have a PCB ruler. That’s what all the hip kids are doing. For wizards and dark mages out there, a simple PCB ruler isn’t enough. These rare beasts demand RF rulers. There’s some weird stuff on these rulers, like Archemedian spiral antennas and spark gaps. Black magic stuff, here.

Some dude with a camera in the woods did something. Primitive Technology, the best example of experimental archaeology you’ve ever seen, built a spear thrower. You can throw a ball faster with a lacrosse stick than you can with just your hands, and this is the idea behind this device, commonly referred to as an atlatl. You can hunt with an atlatl in some states, but I have yet to see a video of anyone taking down a deer with one of these.

Think we’re done spamming the Hackaday Superconference yet? YOU’RE WRONG. The Hackaday Superconference is the greatest hardware conference of all time until we do this whole thing again next year. Get your tickets, look at the incredible list of speakers, book your flights, and be in Pasadena November 5-6.