radio

561 Articles

Long Range WiFi Broadcasts Open-Source Video Conferencing

October 10, 2020 by 18 Comments

WiFi is an ubiquitous feature of the modern landscape, but due to power restrictions on most hardware alongside the high-frequency signal it’s typically fairly limited in range. This of course leads to frustration where a WiFi signal can be seen, but the connection is unreliable or slow. While most would reach for a range extender or other hardware bridge, [tak786] was able to roll out a better solution for his workplace by using a high-gain antenna and a single-board computer which gets him an amazing kilometer-wide WiFi network.

The build uses a 10 dBi antenna from TP-Link that’s rated for outdoor use and a single-board computer which acts as a sort of router. The antenna is placed at the top of a building which certainly helps with the extreme range as well. This setup doesn’t actually broadcast an open Internet connection, though. [tak786]’s employer needed a teleconferencing solution for their building, and he also created a fully open-source video conferencing solution called trango that can run on any LAN and doesn’t require an Internet connection. The WiFi setup in this build is effectively just a bonus to make the conferencing system more effective.

[tak786] is planning on releasing a whitepaper about this build shortly, but for now you can access the source code for the video conferencing system at his GitHub page. And, before anyone jumps to conclusions, apparently this is well within FCC rules as well. Some of the comments in the linked Reddit post suggest that with an amateur radio license this system could be pushed much further, too. If you need more range than a kilometer, though, it’s not too much more difficult to do once you have all the right hardware.

SDR Transmitting Gets The Power

August 29, 2020 by 28 Comments

Most hobby-grade software defined radio setups don’t transmit. Of the few that do, most of them put out anemic levels around one milliwatt or so. If you want to do something outside of the lab, you’ll need an amplifier and that’s what [Tech Minds] shows how to do in a recent video. (Embedded below.)

The video covers LimeSDR, HackRF, and the Pluto SDR, although the amplifiers should work with any transmitter. The SPF5189Z module is quite cheap and covers 50 MHz to 4 GHz, amplifying everything you throw at it. The downside is that it will amplify everything you throw at it, even parts of the signal you don’t want, such as spurs and harmonics.

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Ham Radio Mobile Operations Circa 1919

July 16, 2020 by 16 Comments

You used to be able to tell a die-hard ham radio operator on the road by the number and length of antennas protruding porcupine-like from their vehicle. There are still some mobile high frequency operators that have respectable car-mounted antenna farms, but they have nothing on Alfred H. Grebe. In 1919, he fitted a medium wave transmitter in his car that operated around 2 MHz. Since it needed a very large antenna, Grebe rigged a wire antenna that looked like a clothesline between the two bumpers. Obviously, you had to stop, set up your antenna, and then operate — you couldn’t talk and drive. But this may have been the world’s first automotive radio setup for voice communication.

The car had a separate battery for the radio and a dynamotor to generate high voltage for the tubes. Although many radio enthusiasts found ways to add receivers to their cars in the 1920s, it would be 1930 before Motorola made radios especially for cars in production quantities.

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Faux Vintage Radio Gets AirPlay Upgrade

June 28, 2020 by 1 Comment

There’s plenty of vintage-styled hardware out these days, with quality and functionality being mixed at best. [Huan] found such a device in the form of an attractively-styled Bluetooth speaker. Deciding he could improve on the capabilities while retaining a stock look, he got down to hacking.

The aim of the project was to keep the original volume knob, buttons and screen, while replacing the internals with something a bit more capable. A Raspberry Pi Zero was sourced as the brains of the operation, with the Google Voice AIY hardware used as the sound output after early attempts with a discrete amplifier faced hum issues. An Arduino Pro Micro was pressed into service to read the volume encoder along with the buttons and drive the charlieplexed LED screen. Shairport Sync was then installed on the Pi Zero to enable Airplay functionality.

It’s a basic hack that nonetheless gives [Huan] an attractive AirPlay speaker, along with plenty of useful experience working with Arduinos and Raspberry Pis. We’ve seen similar hacks before, too. If you’re working on your own stereo resurrection at home, be sure to drop us a line!

433 On A Stick

June 27, 2020 by 15 Comments

Cheap 433 MHz wireless switches are a tempting way to enter the world of home automation, but without dedicated hardware, they can be less easy to control from a PC. That’s the position [TheStaticTurtle] was in, so the solution was obvious. Build a USB 433 MHz transceiver.

At the computer end is a CH340 USB-to-serial chip and the familiar ATmega328 making this a compact copy of the Arduino. At the RF end are a pair of modules for transmit and receive, unexpectedly with separate antennas. This device is a second revision, after initial experiments with a single antenna connector and an RF switch proved not to work. On the software side the Arduino uses the rc-switch library, while on the PC side there’s a Python library to make sense of it all. The code and hardware files are all on GitHub, should you wish to experiment.

The problem of making a single antenna transceiver is not for the faint-hearted RF engineer, as while diode switches seem on paper to deliver the goods, they can be extremely difficult to get right and preserve linearity. We’re curious that a transceiver module wasn’t used instead, but we’re guessing that cost played a significant part in the equation.

Over the years we’ve featured quite a few fascinating 433 MHz projects, like this TP-Link router conversion.

Rotary Phone Takes You Around The World And Through Time – With Music

June 24, 2020 by 5 Comments

Purposely choosing obsoleted technology combines all the joy of simpler times with the comfort of knowing you’re not actually stuck with outdated (and oftentimes inferior) technology. The rotary phone is a great example here, and while rarely anyone would want to go back to the lenghty, error-prone way of dialing a number on it on an everyday basis, it can definitely add a certain charm to a project. [Caroline Buttet] thought so as well, and turned her grandma’s old rotary phone into a time-traveling, globe-trotting web radio.

The main idea is fairly simple: a Raspberry Pi connects via browser to a web radio site that plays music throughout the decades from places all over the world. [Caroline]’s implementation has a few nice twists added though. First of all, the phone of course, which doesn’t only house the Raspberry Pi, but serves both as actual listening device via handset speaker, and as input device to select the decade with the rotary dial. For a headless setup, she wrote a Chromium extension that maps key events to virtual clicks on the corresponding DOM element of the web site — like the ones that change the decade — and a Python script that turns the rotary dial pulses into those key events.

However, the phone is only half the story here, and the country selection is just as fascinating — which involves an actual world map. An audio connector is attached to each selectable country and connected to an Arduino. If the matching jack is plugged into it, the Arduino informs the Raspberry Pi via serial line about the new selection, and the same Chromium extension then triggers the country change in the underlying web site. You can check all the code in the project’s GitHub repository, and watch a demo and brief explanation in the videos after the break.

Sure, listening radio through a telephone may not be the most convenient way — unless it’s the appropriate genre — but that clearly wasn’t the goal here anyway. It’s definitely an interesting concept, and we could easily see it transferred to some travel- or spy-themed escape room setting. And speaking of spying, if [Caroline]’s name sounds familiar to you, you may remember her virtual peephole from a few months back.

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Tackling Trunked Radio With Software

June 16, 2020 by 12 Comments

For those starting to wade into radio as a hobby, one of the first real technical challenges is understanding trunked radio systems. On the surface, it seems straightforward: A control channel allows users to share a section of bandwidth rather than take up one complete channel, allowing for greater usage of the frequency range. In practice though it can be difficult to follow along, but now it’s slightly easier thanks to software defined radio.

This guide comes to us from [AndrewNohawk], who is located in San Francisco and is using his system to monitor police, fire, and EMS activity. These groups typically used trunked radio systems due to the large number of users. For listening in, nothing more than an RTL-SDR setup is needed, and the guide walks us through using this setup to find the control channels, the center frequency, and then identifying the “talk groups” for whichever organization you want to listen in on.

The guide goes into great detail, including lists of software needed to get a system like this started up, and since [AndrewNohawk] is a self-identified “radio noob” the guide is perfectly accessible to people who are new to radio and specifically new to trunked systems like these. Once you get the hang of it, it’s not too hard to scale up, either.