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2017

  Taking extra care in the lands of the large and the small

Recently, I found myself peering at a dial indicator while checking the blade runout on my shiny new 12-inch miter saw. I’m putting up new trim in my house, and the big blade allows me to make some cuts directly on larger assemblies. However, I’m no professional woodworker, so my motto is when in doubt, measure... and measure again.

Given the size of the blade, details such as its flatness and mounting are especially important to making good cuts and tight joints. These factors got me thinking of recent developments at the other end of the scale in our RF work, namely the small physical geometry of the millimeter-frequency hardware we’re increasingly using to send information or sense things.

The new N9041B UXA X-Series signal analyzer and its two different input connectors are good examples of what happens when you scale frequencies up and geometries down.

Comparing the two RF/millimeter frequency inputs of the Keysight UXA 110 GHz signal analyzer.  The full frequency range is available from the 1 mm connector of RF input 2, while the 2.4 mm connector of RF input 1 provides a more rugged connection when frequency coverage to 50 GHz is sufficient

The two coaxial input connectors on the UXA signal analyzer have different characteristics and capabilities. The 2.4 mm connector of input 1 (left) covers frequencies to 50 GHz with a power limit of 1W. The 1 mm connector (right) covers frequencies to 110 GHz and power levels to 1.8 mW.

RF Input 1 is a normal 2.4 mm front-panel connector and, as is common with test equipment, the gender is male to reduce the chance of damage and encourage the use of adapters as connector savers. This separate input provides several benefits for users of the UXA when measuring signals below 50 GHz. It’s more mechanically robust than 1 mm or 1.85 mm connectors. It can also handle much more power without damage: 1 W vs. 0.0018 W for RF Input 2.

RF input 2 is also male, and has the more complicated and challenging job: covering higher frequencies with its smaller and more delicate geometry.

In addition to its conductor size, two mechanical differences are apparent. First, the connector body has an additional, larger outer thread ring to mate with test-port adapters rather than standard 1 mm adapters. These adapters are mechanically stronger and less susceptible to damage, and are the best way to connect to the 1 mm input (if they’re available).

The second difference is the pair of threaded bosses, one on either side of the connector. These bosses are used to mount an input-connector vise assembly, perhaps the smallest vise you’ll ever use.

The 1 mm 110 GHz RF input 2 of the UXA signal analyzer can be fitted with a vise or clamp assembly to isolate the connector from the higher torque that may be needed for other connectors, cables or adapters.

A small vise or clamp assembly is attached around the 1 mm, 110 GHz input of the UXA signal analyzer, isolating the mounting torque for the adapter from the torque needed for connecting the adapter to cables, waveguide adapters, etc.

The small size of the 1 mm connectors mean that they don’t need—and probably won’t withstand—the torque that’s appropriate for larger connectors. The torque for the 1 mm connector is 3 or 4 inch-pounds, while the torque for 1.85 mm and larger microwave connectors is 8 inch-pounds.

This is a formula for very expensive damage! To prevent it, the vise holds the flats (part of the body) of the 1 mm end of a standard adapter after it has been tightened to the analyzer’s front panel connector, avoiding the transfer of torque used to connect cables or other adapters to the adapter mounted to the instrument.

As discussed here before, torque is important at microwave and millimeter frequencies. DUT connections are difficult enough, and this simple little clamp can neutralize an important source of problems. You can learn more in the connector kit overview.

As for me, if I had just purchased one of these expensive 110 GHz analyzers, I’d be tempted to quickly stencil a warning around the 1 mm connector in fluorescent green: maybe “Are you sure?” or “Are you authorized to use this port?” You can never be too careful in the land of the very small.

benz

It’s RF interference again…

Posted by benz Jul 10, 2017

  The case of the troublesome garage door opener

 

Note from Ben: This is the first in a series of guest posts from Jennifer Stark of Keysight. As discussed here earlier, our increasingly crowded RF environment will result in more interference, and a higher likelihood of it causing problems. To stay ahead of them, you’ll need your creativity, deductive skills, and persistence

 

Interference is everywhere. And often from an unlikely source.

Let's take the case of an engineer (we’ll call him Mike) who recently had a problem with his garage door opener. Mike had recently installed a new garage door opener. Frustratingly, the garage door remotes that our Mike and his wife carried in their cars intermittently failed to activate the garage door opener.

As a first step, Mike called the support line for the manufacturer of the garage door opener to report the defective product. The installation support person walked Mike through a troubleshooting procedure over the phone. The procedure did not identify any reason that the hardware should be defective. At that point, the installation support person gravely pronounced “You have something called RF interference. That’s your problem, not ours.”

It turns out that Mike is an RF engineer, so he took this as an interesting challenge.

Mike used his N9912A FieldFox handheld RF analyzer in spectrum analyzer mode. He cobbled together a homemade antenna for the input connector and started sniffing around the house for RF interference. He identified the target frequencies by pressing the garage door remote button while looking at the RF spectrum.

Waterfall and spectrogram displays are a way to visually understand the time domain behavior and frequency of occurrence of signals and interference. This display is from a handheld spectrum analyzer with additional software that helps in detecting and visualizing interference.

Waterfall and spectrogram displays are useful for spotting interference and understanding its behavior in the time domain. The N9918A-236 Interference Analyzer and Spectrogram software for FieldFox analyzers adds these displays to spectrum measurements.

Armed with this information about the frequency range of interest, Mike set out looking for any signals that were near the frequency of the garage door opener. A diligent engineer, he went all over the house looking for clues. He looked in the garage. He looked upstairs in the house, above the garage. He looked in corners of the house.

Eventually, he discovered a small but significant signal in the kitchen. It appeared to be coming from the refrigerator. This puzzled Mike, but his engineering discipline compelled him to investigate. Unplugging the refrigerator did not eliminate the signal. Checking at a different time of day, Mike discovered that the interfering signal was absent even when the refrigerator was operating. It was a mystery.

Leaning on the kitchen counter to collect his thoughts, Mike took stock of what he had learned:  intermittent garage door issues, signal coming from the kitchen. Then, Mike had an insight. The garage door only failed when his wife was home, so the issue was related to the comings and goings of his wife.

At this point, Mike noticed his wife’s purse in its normal spot on the counter by the refrigerator. Mike investigated his wife’s purse with his FieldFox. Sure enough, the interfering signal was coming from the purse (not from the refrigerator). Inside the purse was the remote key fob for the car. Mike removed the battery from the key fob and the interfering signal immediately went away.

The solution was simple—replace the troublesome key fob. Now the garage door is working properly, Mike is happy, and Mike’s wife is happy. And, the pesky RF interference is no more.

  Engineers that exemplify creativity, and the ability to explain it

School is out and some are on holiday. It’s a good time to briefly widen this blog’s technology focus a bit with one of my occasional off-topic wanderings. This time we’ll look at impressive achievements of some engineers of yore, and a couple of enlightening explanations of their creations.

These days we combine our electrical skill with processors, software, and myriad actuator types to generate virtually any kind of complex mechanical action—wherever we need to connect electrons with the physical world. It’s easy to forget how sophisticated tasks were accomplished in the past, without computers or stepper motors, and how even advanced techniques such as perceptual coding were implemented with physical mechanisms.

All these elements were brought together for me recently in an impressive YouTube explanation by “engineerguy” Bill Hammack of the University of Illinois. In just four minutes, Bill explains several poorly understood aspects of film projectors that evolved in the century between their invention (c.1894) and their replacement by digital cinema technology (c.1999).

Bill uses slow-motion footage and animated diagrams to do a great job of explaining how a projector keeps the film going smoothly across the sound sensor while intermittently starting and stopping the film between the lamp and lens. This precisely executed start-stop motion, projecting the film image only when it isn’t moving, coaxes our vision system into seeing a series of stills as fluid motion.

Bill shows how the motion is produced using a synchronized cam, shuttle, and wobble plate. As I dug deeper, further research showed that some projectors instead use an equally innovative mechanism called a Geneva drive (or Geneva stop), a mechanism that was already old when the first crude projectors were created in the late 19th century. Seeing the shape of the Geneva mechanism sent me to my reproduction of the very old book Five Hundred & Seven Mechanical Movements.

Scanned image of Geneva mechanism or Geneva stop from 1889 book Five Hundred & Seven Mechanical Movements

This composite figure shows two examples of Geneva drives from the mechanisms in Henry T. Brown’s 1896 book Five Hundred & Seven Mechanical Movements. These convert continuous motion to intermittent motion with smooth starts and stops, and have built in limits or “stops.”

I figured I was nearly alone in my interest in in the old book, but that is not the case. Another quick search revealed that these manifold fruits of the Industrial Revolution have been brought into the internet age, with hyperlinks and animation at 507movements.com. The animations are addictive!

The book is a potent antidote to the tendency to forget how clever and imaginative the engineers of the past actually were, though they were often self-taught and worked with limited materials. And, if we take Edison and the Wright Brothers as examples, they were tireless experimenters.

From an 1896 book to the joys of YouTube, there is cleverness in both the engineering and the explaining. If you’re looking for something closer to our RF home, check out Bill’s demonstration of performing Fourier analysis with a mechanical device. You may never think of FFTs in quite the same way again.