Simple Scanner Finds the Best WiFi Signal

Want to know which way to point your WiFi antenna to get the best signal? It’s a guessing game for most of us, but a quick build of a scanning WiFi antenna using mostly off-the-shelf components could point you in the right direction.

With saturation WiFi coverage in most places these days, optimizing your signal might seem like a pointless exercise. And indeed it seems [shawnhymel] built this more for fun than for practical reasons. Still, we can see applications where a scanning Yagi-Uda antenna would come in handy. The build started with a “WiFi divining rod” [shawnhymel] created from a simple homebrew Yagi-Uda and an ESP8266 to display the received signal strength indication (RSSI) from a specific access point. Tired of manually moving the popsicle stick and paperclip antenna, he built a two-axis scanner to swing the antenna through a complete hemisphere.

The RSSI for each point is recorded, and when the scan is complete, the antenna swings back to the strongest point. Given the antenna’s less-than-perfect directionality — [shawnhymel] traded narrow beam width for gain — we imagine the “strongest point” is somewhat subjective, but with a better antenna this could be a handy tool for site surveys, automated radio direction finding, or just mapping the RF environment of your neighborhood.

Yagi-Uda antennas and WiFi are no strangers to each other, whether it be a WiFi sniper rifle or another recycling bin Yagi.  Of course this scanner isn’t limited to WiFi. Maybe scanning a lightweight Yagi for the 2-meter band would be a great way to lock onto the local Ham repeater.

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Pi Network Attenuators: Impedance Matching For The Strong Of Signal

If you catch a grizzled old radio amateur propping up the bar in the small hours, you will probably receive the gravelly-voiced Wisdom of the Ancients on impedance matching, antenna tuners, and LC networks. Impedance at RF, you will learn, is a Dark Art, for which you need a lifetime of experience to master. And presumably a taste for bourbon and branch water, to preserve the noir aesthetic.

It’s not strictly true, of course, but it is the case that impedance matching at RF with an LC network can be something of a pain. You will calculate and simulate, but you will always find a host of other environmental factors getting in the way when it comes down to achieving a match. Much tweaking of values ensues, and probably a bit of estimating just how bad a particular voltage standing wave ratio (VSWR) can be for your circuit.

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4.4 GHz Frequency Synthesis Made Easy

How hard is it to create a synthesizer to generate frequencies between 35 MHz to 4.4 GHz? [OpenTechLab] noticed a rash of boards based on the ADF4351 that could do just that priced at under $30. He decided to get one and try it out and you can find his video results below.

At that price point, he didn’t expect much from it, but he did want to experiment with it to see if he could use it as an inexpensive piece of test gear. The video is quite comprehensive (and weighs in at nearly an hour and a half). It covers not just the device from a software and output perspective but also talks about the theory behind these devices.  [OpenTechLab] even sniffed the USB connection to find the protocol used to talk to the device. He wasn’t overly impressed with the performance of the board but was happy enough with the results at the price and he plans to make some projects with it.

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RadiantBee Is A Flying Microwave Antenna Calibration System

Many of the projects we link to here at Hackaday have extensive write-ups, pages of all the detail you could need. Sometimes though we happen upon a project with only a terse description to go on, but whose tech makes it one worth stopping for and unpicking the web of information around it.

Such a project is [F4GKR] and [F5OEO]’s RadiantBee, an attempt to use a beacon transmitter on a multirotor as an antenna calibration platform. (For more pictures, see this Twitter feed.) In this case a multirotor has a GPS and a 10 GHz beacon that emits 250 ms chirps, from which the receiver can calculate signal-to-noise ratio as well as mapping the spatial response of the antenna.

The transmitter uses a Raspberry Pi feeding a HackRF SDR and a 10 GHz upconverter, while the receiver uses an RTL-SDR fed by a 10 GHz to 144 MHz downconverter. The antennas they are testing are straightforward waveguide horns, but the same principles could be applied to almost any antenna.

There was a time when antenna design at the radio amateur level necessitated extensive field testing, physical measurements with a field strength meter over a wide area, correlation of figures and calculation of performance. But with computer simulation the field has become one much more set in the lab, so it’s rather refreshing to see someone producing a real-world simulation rig. If you ever get the chance to evaluate an antenna through real-world measurement, grasp it with both hands. You’ll learn a lot.

We’ve covered very few real-world antenna tests, but there is mention in this write-up of a radar antenna test of a measurement session on a football field.

Via Southgate ARC.

A Walk-In Broadcast Transmitter

[Mr. Carlson] likes electronics gear. Mostly old gear. The grayer the case, the greener the phosphors, and the more hammertone, the better. That’s why we’re not surprised to see him with a mammoth AM radio station transmitter in his shop. That it’s a transmitter that you can walk into while it’s energized was a bit of a surprise, though.

As radio station transmitters go, [Mr. Carlson]’s Gates BC-250-GY broadcast transmitter is actually pretty small, especially for 1940s-vintage gear. It has a 250 watt output and was used as a nighttime transmitter; AM stations are typically required to operate at reduced power when the ionosphere is favorable for skip on the medium frequency bands. Stations often use separate day and night transmitters rather than just dialing back the daytime flamethrower; this allows plenty of time for maintenance with no interruptions to programming.

If you enjoy old broadcast gear, the tour of this transmitter, which has been rebuilt for use in the ham bands, will be a real treat. Feast your eyes on those lovely old bakelite knobs and the Simpson and Westinghouse meters, and picture a broadcast engineer in white short sleeves and skinny tie making notations on a clipboard. The transmitter is just as lovely on the inside — once the plate power supply is shut down, of course, lest [Mr. Carlson] quickly become [the former late Mr. Carlson] upon stepping inside. Honestly, there aren’t that many components inside, but what’s there is big – huge transformer, giant potato slicer variable caps, wirewound resistors the size of paper towel tubes, and five enormous, glowing vacuum tubes.

It’s a pretty neat bit of broadcasting history, and it’s a treat to see it so lovingly restored. [Mr. Carlson] teases us with other, yet larger daytime transmitters he has yet to restore, and we can’t wait for that tour. Until then, perhaps we can just review [Mr. Crosley]’s giant Cincinnati transmitter from the 1920s and wait patiently.

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The Right Circuit Turns Doppler Module into a Sensor

Can you buy a working radar module for $12? As it turns out, you can. But can you make it output useful information? According to [Mathieu], the answer is also yes, but only if you ignore the datasheet circuit and build this amplification circuit for your dirt cheap Doppler module.

The module in question is a CDM324 24-GHz board that’s currently listing for $12 on Amazon. It’s the K-band cousin of the X-band HB100 used by [Mathieu] in a project we covered a few years back, but thanks to the shorter wavelength the module is much smaller — just an inch square. [Mathieu] discovered that the new module suffered from the same misleading amplifier circuit in the datasheet. After making some adjustments, a two-stage amp was designed and executed on a board that piggybacks on the module with a 3D-printed bracket.

Frequency output is proportional to the velocity of the detected object; the maximum speed for the sensor is only 14.5 mph (22.7 km/h), so don’t expect to be tracking anything too fast. Nevertheless, this could be a handy sensor, and it’s definitely a solid lesson in design. Still, if your tastes run more toward using this module on the 1.25-cm ham band, have a look at this HB100-based 3-cm band radio.

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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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