AM Radio Broadcast Uses Phasor To Let Eight Towers Spray One Big Signal

April 20, 2024 by Lewin Day 8 Comments

If you’re in the commercial AM radio business, you want to send your signal as far and wide as possible. More listeners means you can make more ad revenue, after all. [Jeff Geerling] recently visited a tower site for WSDZ-AM, which uses a full eight towers to broadcast its 20kW AM signal. To do that, it needs a phasor to keep everything in tune. Or, uh… phase.

The phasor uses a bunch of variable inductors and capacitors to manage the phase of the signal fed to each tower. Basically, by varying the phase of the AM signal going to each of the 8 transmitter towers, it’s possible to tune the directionality of the tower array. This allows the station to ensure it’s only broadcasting to the area it’s legally licensed to do so.

The tower array is also configured to broadcast slightly differently during the day and at night to account for the differences in propagation that occur. A certain subset of the 8 towers are used for the day propagation pattern, while a different subset is used to shape the pattern for the night shift. AM signals can go far farther at night, so it’s important for stations to vary their output to avoid swamping neighbouring stations when the sun goes down.

[Jeff’s] video is a great tour of a working AM broadcast transmitter. If you’ve ever wondered about the hardware running your local commercial station, this is the insight you’re looking for. AM radio may be old-school, but it continues to fascinate us to this day. Video after the break.

Continue reading “AM Radio Broadcast Uses Phasor To Let Eight Towers Spray One Big Signal” →

Measuring An Unknown Velocity Factor

April 19, 2024 by Al Williams 14 Comments

When is the speed of light not the speed of light? Of course, that’s a trick question. The speed of light may be constant, but just as sound travels at different speeds in different media, electronic signals move through transmission lines at a reduced speed. When you have a known cable, you can look up the velocity factor and use it to approximate the length of cable to have a given effective length. But what if you don’t know what kind of cable you have? [More Than Electronics] used a scope to measure it. You can see what he did in the video below.

For example, RG-8/U has a factor of 0.77. Even air isn’t exactly a factor of 1, although it is close enough that, in practice, we pretend that it is. If you wonder why it matters, consider stubs. Suppose you have a 300 MHz signal (handy because that’s 1 meter in wavelength; well, OK, pick 299.792 MHz if you prefer). If you have a quarter wavelength piece of coax shorted at one end, it will attenuate signals at 300 MHz. To understand why, picture the wave on the stub. If the close end of the stub is at 0 volts, then the other end — because it is a quarter wavelength away — must be at the maximum positive voltage or the minimum negative voltage. If either of the extremes is at the close end, then the far end must be at zero volts. That means the maximum current flows only when the signal is at 300 MHz.

Continue reading “Measuring An Unknown Velocity Factor” →

Crystal Radio Kit From The 1970s

April 19, 2024 by Al Williams 19 Comments

If you read the December 1970 issue of Mechanix Illustrated, you’d be treated to [Len Buckwalter]’s crystal radio build. He called out Modern Radio Labs as the supplier for parts. That company, run by [Elmer Osterhoudt], got so many inquiries that he produced a kit, the #74 crystal set. [Michael Simpson] found an unopened kit on eBay and — after a bidding war, took possession of the kit. The kit looked totally untouched. The crystal detector was still in the box, and there were period-appropriate newspaper wrappings.

The kit itself isn’t that remarkable, but it is a classic. An oatmeal box serves as a coil form. There’s a capacitor, a crystal detector, and headphones. The original cost of the parts was $7, but we imagine the eBay auction exceeded that by a large amount.

If the name [Len Buckwalter] sounds familiar, he was quite prolific in magazines like Electronics Illustrated and also wrote several books about transistors. [Michael] also shows off his innovative coil winder made from plastic cups and a coat hanger.

We’d love to find some old kits like this, although, from one way of thinking, it is almost a shame to build them after all these years. With an added audio amplifier and fiddling with the cat whisker, it sounded just fine.

If you don’t like oatmeal, you could fire up the 3D printer. While the basic circuit is simple, you can make it more complex if you like.

Continue reading “Crystal Radio Kit From The 1970s” →

Getting Started With Radio Astronomy

April 17, 2024 by Al Williams 11 Comments

There are many facets to being a radio hobbyist, but if you’ve ever had the urge to dabble in radio astronomy, check out “The Novice’s Guide to Amateur Radio Astronomy,” a presentation at the 2024 conference of the Society of Amateur Radio Astronomers. In that presentation (see the video below), [Nathan Butts] covers everything from why you should take up the hobby, how to set up a software defined radio (SDR) receiver, and how to repurpose old computers. This is just one of a series of videos recently posted from the conference — check out their channel to see them all.

Unlike optical astronomy, you can listen to the universe by radio during the day or night, rain or shine. You don’t need a dark sky, although these days, a quiet radio location might be hard to find. [Nathan] also points out that some people just want to crunch data collected by others, and that’s fun, too. There are many ways to get involved from designing hardware, writing software, or — of course — just listening.

It has never been easier to get involved. Cheap software-defined radios are perfect for this sort of work, and we all have massive computers and scores of small data-collection computers. Maybe you’ll be the next person to hear a Wow signal. If you are worried about fielding an antenna, many people repurpose satellite dishes.

Continue reading “Getting Started With Radio Astronomy” →

M17 Digital Communications Go From Strength To Strength

April 13, 2024 by Jenny List 6 Comments

The world of amateur radio is like many other fields in that there has been a move underway from analogue to digital modes. In fact, amateur radio has often led the way in digital innovation. There’s a snag, though: many of the digital speech modes are proprietary. To address this along comes the M17 project, an effort to create an open digital communication protocol for radio amateurs. We’ve looked at them more than once in the past few years, and as they’ve come up with several pieces of new hardware it’s time for another peek.

First up is the Remote Radio Unit, described as “a comprehensive, UHF FM/M17 “repeater in a box,” optimally designed for close antenna placement, enhancing signal strength and reliability.” The repeater forms the “other half” of the UHF handheld radio chain and will be crucial to the uptake of the protocol.

Continue reading “M17 Digital Communications Go From Strength To Strength” →

WSPR To The Wind With A Pi Pico High Altitiude Balloon

April 11, 2024 by Richard Baguley 19 Comments

They say that if you love something, you should set it free. That doesn’t mean that you should spend any more on it than you have to though, which is why [EngineerGuy314] put together this Raspberry Pi Pico high-altitude balloon tracker that should only set you back about $12 to build.

This simplified package turns a Pico into a tracking beacon — connect a cheap GPS module and solar panel, and the system will transmit the GPS location, system temperature, and other telemetry on the 20-meter band using the Weak Signal Propagation Reporter (WSPR) protocol. Do it right, and you can track your balloon as it goes around the world.

The project is based in part on the work of [Roman Piksayin] in his Pico-WSPR-TX package (which we covered before), which uses the Pico’s outputs to create the transmitted signal directly without needing an external radio. [EngineerGuy314] took this a step further by slowing down the Pico and doing some clever stuff to make it run a bit more reliably directly from the solar panel.

The system can be a bit fussy about power when starting up: if the voltage from the solar panel ramps up too slowly, the Pico can crash when it and the GPS chip both start when the sun rises. So, a voltage divider ties into the run pin of the Pico to keep it from booting until the voltage is high enough, and a single transistor stops the GPS from starting up until the Pico signals it to go.

It’s a neat hack that seems to work well: [EngineerGuy314] has launched three prototypes so far, the last of which traveled over 62,000 kilometers/ 38,000 miles.

Emails Over Radio

April 9, 2024 by Bryan Cockfield 38 Comments

The modern cellular network is a marvel of technological advancement that we often take for granted now. With 5G service it’s easy to do plenty of things on-the-go that would have been difficult or impossible even with a broadband connection to a home computer two decades ago. But it’s still reliant on being close to cell towers, which isn’t true for all locations. If you’re traveling off-grid and want to communicate with others, this guide to using Winlink can help you send emails using a ham radio.

While there are a number of ways to access the Winlink email service, this guide looks at a compact, low-power setup using a simple VHF/UHF handheld FM radio with a small sound card called a Digirig. The Digirig acts as a modem for the radio, allowing it to listen to digital signals and pass them to the computer to decode. It can also activate the transmitter on the radio and send the data from the computer out over the airwaves. When an email is posted to the Winlink outbox, the software will automatically send it out to any stations in the area set up as a gateway to the email service.

Like the cellular network, the does rely on having an infrastructure of receiving stations that can send the emails out to the Winlink service on the Internet; since VHF and UHF are much more limited in range than HF this specific setup could be a bit limiting unless there are other ham radio operators within a few miles. This guide also uses VARA, a proprietary protocol, whereas the HF bands have an open source protocol called ARDOP that can be used instead. This isn’t the only thing these Digirig modules can be used for in VHF/UHF, though. They can also be used for other digital modes like JS8Call, FT8, and APRS.

Continue reading “Emails Over Radio” →