A Practical Glue Stick Oscillator

January 5, 2023 by Jenny List 15 Comments

A few months ago we brought you some experiments from [Bill Meara, N2CQR], in which he investigated the use of a glue stick as the former for a permeability tuned inductor. His set-up was very much in the spirit of experimentation, and we’re very pleased to now see [Nick, M0NTV] has taken the idea and demonstrated it for the 7 MHz, or 40 meter, amateur radio band.

The result can be seen in the video below the break, and is housed in a tin enclosure that we’re guessing once contained toffees. The oscillator circuit comes courtesy of [Ashar Farhan VU2ESE] of BitX transceiver fame, but we’re most interested in the glue stick coil former which makes use of a small bracket for stability. With the glue removed, he’s mounted a ferrite ring in its glue carrier which is moved in and out of the coil. We’re guessing this could also be done with other permeability-altering materials, for example we’d follow [VU2ESE]’s lead and try a piece of brass.

The knurled glue feed knob protrudes through a hole in the tin, and we’re guessing there’s enough separation for an operator’s hand not to drag the frequency too much. All in all given that variable capacitors are now something of a rarity, it makes for a useful demonstration of a very cheap replacement. Meanwhile, you can read our notes on [N2CQR]’s work here.

Continue reading “A Practical Glue Stick Oscillator” →

AIOC: The Ham Radio All-In-One Cable For Audio And APRS

January 1, 2023 by Dave Rowntree 23 Comments

The Ham Radio All-in-one cable (AIOC) is a small PCB attachment for a popular series of radio transceivers which adds a USB-attached audio interface and virtual TTY port for programming and the push-to-talk function. The STM32F373 microcontroller (which, sadly is still hard to find in the usual channels) is a perfect fit for this application, with all the needed hardware resources.

With USB-C connectivity, the AIOC enumerates as a sound card as well as a virtual serial device, so interfacing to practically any host computer should be plug-and-play. Connection to the radio uses 12mm separation 3.5mm and 2.5mm TRS connectors, so is compatible with at least the Baofeng UV-5R but likely many other cheap transceivers that have the same physical setup.

Instructions are provided to use the AIOC with Dire Wolf for easy access to APRS applications, which makes a nice out-of-the-box demo to get you going. APRS is not all about tracking things though since other applications can sit atop the APRS/AX.25 network, for example, HROT: the ham radio of things.

We’ve seen quite a few Baofeng (and related products) hacks, like this sketchy pile of wires allowing one to experiment with the guts of the radio for APRS. Of course, such cheap radio transceivers cut so many engineering corners that there are movements to ban their sale, so maybe a new batch of better radios from our friends in the East is on the horizon?

Thanks to [Hspil] for the tip!

Working With I2S-Compatible FM Tuners

December 23, 2022 by Lewin Day 9 Comments

While the Internet is a great place to get access to any music or audio you can dream of, there’s still a place for broadcast radio. [mit41301] has recently been exploring implementing a simple FM tuner chip in various projects.

The chip in question is the RDA7088, which is designed to require the bare minimum in external components, and is available in a compact SOP16 package. As per the datasheet, it was intended for use in applications like portable radios, PDAs, cell phones, and MP3 players.

[mit41301]’s first attempt involved using the chip as a simple tuner, hooked up to a PIC10F200 for control. Investigation revealed it was capable of outputting digital audio via I2S, while being commanded via I2C. By default, it spits out audio at a low sample rate of 8 kHz, but reconfiguration will jump that up to 44.1 or 48 kHz. Piping that digital I2S stream out to a DAC then delivers analog output that can be fed to an amplifier. The build also got remote control, with the PIC handling decoding IR signals and outputting commands to the radio chip.

Following this success, [mit41301] then went further, hooking up an ESP-01 to the chip to try and get RDS going. If you’re unfamiliar with the Radio Data System, it’s a way for short textual messages to be sent out by FM broadcasters. In addition to the duties carried out by the PIC module, the ESP-01 is also charged with receiving RDS data from the RDA7088, and outputting it to a display.

While using such chips is routine in industry, it’s always great to see a DIY guide to interfacing with specific hardware. If you want to integrate FM radio into your own projects, the RDA7088 is a simple and easy way to do so. We’ve seen similar work before, adding FM radio to the Raspberry Pi.

Continue reading “Working With I2S-Compatible FM Tuners” →

BBC World Service Turns 90

December 22, 2022 by Al Williams 23 Comments

If you’ve ever owned a shortwave radio, you’ve probably listened at least a little to the BBC World Service. After all, they are a major broadcasting force, and with the British Empire or the Commonwealth spanning the globe, they probably had a transmitter close to your backyard. Recently, the BBC had a documentary about their early years of shortwave broadcasting. It is amazing both because it started so simply and when you think how far communications have progressed in just a scant 100 years.

Today, the BBC World Service broadcasts in over 40 languages distributing content via radio, TV, satellite, and the Internet. Hard to imagine it started with four people who were authorized to spend 10 pounds a week.

Continue reading “BBC World Service Turns 90” →

Citizen-Driven Network Monitors Public Service Radio For Natural Disaster Alerts

December 17, 2022 by Dan Maloney 12 Comments

Time is of the essence in almost every emergency situation, especially when it comes to wildfires. A wind-driven fire can roar across a fuel-rich landscape like a freight train, except one that can turn on a dime or jump a mile-wide gap in a matter of seconds. Usually, the only realistic defense against fires like these is to get the hell out of their way as soon as possible and make room for the professionals to do what they can to stop the flames.

Unfortunately, most people living in areas under threat of wildfires and other natural disasters are often operating in an information vacuum. Official channels take time to distribute evacuation orders, and when seconds count, such delays can cost lives. That’s the hole that Watch Duty seeks to fill.

Watch Duty is a non-profit wildfire alerting, mapping, and tracking service that provides near-real-time information to those living in wildfire country. Their intelligence is generated by a network of experienced fire reporters, who live in wildfire-prone areas and monitor public service radio transmissions and other sources to get a picture of what’s going on in their specific area. When the data indicate an incident is occurring, maps are updated and alerts go out via a smartphone app. Reporters have to abide by a strict code of conduct designed to ensure the privacy of citizens and the safety of first responders.

While Watch Duty’s network covers a substantial area of California — the only state covered so far — there were still a significant number of dead zones, mostly in the more remote areas of the Sierra Nevada Mountains and in the northern coastal regions. To fill these gaps, Watch Duty recently launched Watch Duty Echo, which consists of a network of remote listening posts.

Each station is packed with RTL-SDR receivers that cover a huge swath of spectrum used by the local fire, law enforcement, EMS agencies — any organization likely to be called to respond to an incident. In addition, each station has an SDR dedicated to monitoring ADS-B transponders and air band frequencies, to get a heads-up on incidents requiring aerial support. The listening posts have wideband discone antennas and a dedicated 1090-MHz ADS-B antenna, with either a cellular modem or a Starlink terminal to tie into the Watch Duty network.

Hats off to the folks at Watch Duty for putting considerable effort into a system like this and operating it for the public benefit. Those who choose to live close to nature do so at their own risk, of course, but a citizen-driven network that leverages technology can make that risk just a little more manageable.

Antenna Mount Designed For On-The-Go SDR

December 16, 2022 by Bryan Cockfield 15 Comments

Software-defined radio is all the rage these days, and for good reason. It eliminates or drastically reduces the amount of otherwise pricey equipment needed to transmit or even just receive, and can pack many more features than most affordable radio setups otherwise would have. It also makes it possible to go mobile much more easily. [Rostislav Persion] uses a laptop for on-the-go SDR activities, and designed this 3D printed antenna mount to make his radio adventures much easier.

The antenna mount is a small 3D printed enclosure for his NESDR Smart Dongle with a wide base to attach to the back of his laptop lid with Velcro so it can easily be removed or attached. This allows him to run a single USB cable to the dongle and have it oriented properly for maximum antenna effectiveness without something cumbersome like a dedicated antenna stand. [Rostislav] even modeled the entire assembly so that he could run a stress analysis on it, and from that data ended up filling it with epoxy to ensure maximum lifespan with minimal wear on the components.

We definitely appreciate the simple and clean build which allows easy access to HF and higher frequencies while mobile, especially since the 3D modeling takes it a step beyond simply printing a 3D accessory and hoping for the best. There’s even an improved version on his site here. To go even one step further, though, we’ve seen the antennas themselves get designed and then 3D printed directly.

How On-Frequency Are Those Cheap Radar Modules?

December 6, 2022 by Jenny List 8 Comments

If you’re partial to browsing AliExpress, Banggood, or eBay for unusual hardware, you may have seen the HB100 Doppler Radar modules. These are a PCB with a metal can on board, and their reverse side has a patch antenna array. They work on a frequency of 10.525 GHz, and [OH2FTG] has characterized a few of them to see how close they lie to that figure.

These devices have a superficially very simple circuit that makes extensive use of PCB layout for creating microwave inductors, capacitors, and tuned circuits. There’s a FET oscillator and a diode mixer, and a dielectric resonator coupling the output and input inductors of the FET. This component provides the frequency stability, but its exact frequency depends on what lies within its electric field. Thus the screening can does more than screening, and has a significant effect on the frequency and stability of the oscillator.

The higher quality HB100s have a small tuning screw in the top of the can which in turn adjusts the frequency. This should be tweaked in the factory onto the correct point, but is frequently absent in the cheaper examples. In this case he has a pile of modules, and while surprisingly some are pretty close there are outliers that lie a significant distance away.

If you use an HB100 then the chances are nobody will ever bother you if it’s off-frequency, as its power output is tiny. But it’s worth knowing about their inner workings and also how to adjust them should you ever need to. Meanwhile if you’re interested in Doppler radar, here’s how to design one for a lower frequency.

Continue reading “How On-Frequency Are Those Cheap Radar Modules?” →