Take A Break From Arduinos, And Build A Radio Transmitter

September 30, 2019 by Al Williams 12 Comments

When you start watching [learnelectronic’s] two-part series about making a radio transmitter, you might not agree with some of his history lessons. After all, the origin of radio is a pretty controversial topic. Luckily, you don’t need to know who invented radio to enjoy it.

The first transmitter uses a canned oscillator, to which it applies AM modulation. Of course, those oscillators are usually not optimized for that service, but it sort of works. In part two he reduces the frequency to 1 MHz at which point it can be listened to on a standard AM radio, before adding an amplifier so any audio source can modulate the oscillator. There’s a lot of noise, but the audio is clearly there.

This is far from practical of course, but combined with a crystal radio it could make an awesome weekend project for a kid you want to hook on electronics. The idea that a few simple parts could send and receive audio is a pretty powerful thing. If you get ready to graduate to a better design, we have our collection.

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Probe The Galaxy On A Shoestring With This DIY Hydrogen-Line Telescope

September 29, 2019 by Dan Maloney 6 Comments

Foil-lined foam insulation board, scraps of lumber, and a paint-thinner can hardly sound like the tools of a radio astronomer. But when coupled with an SDR, a couple of amplifiers, and a fair amount of trial-and-error tweaking, it’s possible to build your own hydrogen-line radio telescope and use it to image the galaxy.

As the wonderfully named [ArtichokeHeartAttack] explains in the remarkably thorough project documentation, the characteristic 1420.4-MHz signal emitted when the spins of a hydrogen atom’s proton and electron flip relative to each other is a vital tool for exploring the universe. It lets you see not only where the hydrogen is, but which way it’s moving if you analyze the Doppler shift of the signal.

But to do any of this, you need a receiver, and that starts with a horn antenna to collect the weak signal. In collaboration with a former student, high school teacher [ArtichokeHeartAttack] built a pyramidal horn antenna of insulation board and foil tape. This collects RF signals and directs them to the waveguide, built from a rectangular paint thinner can with a quarter-wavelength stub antenna protruding into it. The signal from the antenna is then piped into an inexpensive low-noise amplifier (LNA) specifically designed for the hydrogen line, some preamps, a bandpass filter, and finally into an AirSpy SDR. GNURadio was used to build the spectrometer needed to determine the galactic rotation curve, or the speed of rotation of the Milky Way galaxy relative to distance from its center.

We’ve seen other budget H-line SDR receiver builds before, but this one sets itself apart by the quality of the documentation alone, not to mention the infectious spirit that it captures. Here’s hoping that it finds its way into a STEM lesson plan and shows some students what’s possible on a limited budget.

Chinese Radio Telescope Hopes To Find Exoplanets FAST

September 28, 2019 by Al Williams 21 Comments

People who enjoy radio are constantly struggling to find a place to erect a bigger and better antenna. Of course it’s a different story and the most hardcore end of the spectrum: radio astronomers. The Chinese are ready to open up a new radio telescope called FAST (Five-hundred-meter Aperture Spherical Radio Telescope). As the name implies, it is 500 meters in diameter which is about 1,600 feet — that five and a half American football fields or about four and half of the other kind of football field.

The new telescope will be the largest single-dish observatory in the world and will offer about twice the area of the next-largest single-dish instrument at Arecibo. The project is in a very remote location, presumably to reduce the level of local radio interference — it’s hard to find radio quiet zones in heavily populated areas.

Scientists hope the huge antenna will help solve the mystery of fast radio bursts and may even study exoplanets. In fact, earlier this year, the instrument detected hundreds of fast radio bursts from a source, many of which were too faint to be heard by lesser antennas. There are also plans to examine pulsars in an attempt to discover ripples in space-time. The location in the Dawodang depression of the Guizhou province uses about 4,400 panels and 2,000 mechanical winches to focus radio energy.

Other telescopes that use multiple dishes have more resolution and, in fact, FAST adds 3 dozen 5 meter commercial dishes to get an increase in resolution of 100 times. Of course, you could build your own, although to get up to 500 meters might be a stretch. If your backyard isn’t that big, you can build a tiny radio telescope too.

Hackable Ham Radio Multitool Contributes To Long Term Survival Of The Hobby

September 18, 2019 by Danie Conradie 28 Comments

Ham radio, especially the HF bands, can be intimidating for aspiring operators, many being put off by the cost of equipment. The transceiver itself is only part of the equation and proper test and measurement equipment can easily add hundreds of dollars to the bill. However, such equipment goes a long way to ease the frustrations of setting up a usable station. Fortunately [Ashhar Farhan, VU2ESE] has been at it again, and recently released the Antuino, an affordable, hackable test instrument for ham radio and general lab for use.

As you can probably guess from the name, it is primarily intended for testing antennas, and uses an Arduino Nano as a controller. It has quite a list of measurement functions including SWR, field strength, cable loss, RF cable velocity, modulation, and frequency response plotting. It also provides a signal source for testing. Its frequency range includes the HF and VHF bands, and it can even work in the UHF bands (435Mhz) if you are willing to sacrifice some sensitivity. The software is open source and available with the schematics on Github.

Most of the active ham radio operators today are of the grey haired, retired variety. If the hobby is to stand any chance of outliving them, it needs to find a way to be attractive to the younger generations who grew up with the internet. The availability of affordable and hackable equipment can go long way to making this happen, and [Ashhar Farhan] has been one of the biggest contributors in this regard. His $129 μBITX HF SSB/CW transceiver kit is by far the best value for money general coverage HF radio available.

See a short demonstration of the Antuino video after the break

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Learn Morse Code, Clockwork Orange Style

September 10, 2019 by Al Williams 11 Comments

You might have to provide your own wrist straps and eye clamps, but if you want to learn Morse code, [Seth] has a web site for you. You can get code practice using the Farnsworth method and each letter is flashed before you as it is sent, which we assume will burn it into your brain.

Why learn Morse code now? Just about all countries now have at least some no code ham licenses and many have taken code off the tests completely. However, there are still many hams that use the code even today. Why? The personal challenge is part of it and perhaps nostalgia. However, it is also true that Morse code transmitters and receivers are dead simple to build and can get through where other simple radios can’t.

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Complex Impedances Without The Pain

September 7, 2019 by Jenny List 13 Comments

Any grizzled electronic engineer will tell you that RF work is hard. Maintaining impedance matching may be a case of cutting wires to length at lower frequencies, but into the low centimetre and millimetre wavelengths it becomes a Dark Art aided by mysterious and hugely expensive test equipment beyond the reach of mere mortals. A vector network analyser or VNA may be beyond the reach of many, but [Tomasz Wątorowski] is here to tell us about how with some resistors, mathematics, and a bit of lateral thinking its functions may be replicated with a more modestly equipped bench.

It’s not a method for the faint-hearted as the mathematics are of the variety that you probably learned as an undergraduate but let slip from your memory with thanks after the course ended. The method involves measuring the return loss both with and without a resistor of known value in series with the antenna, these figures allow the real and imaginary components of the antenna’s impedance to be calculated. There is a further piece of work though, this method doesn’t determine whether the antenna is capacitive or inductive. Repeating the measurement with either a capacitive or inductive matching network allows this to be determined, and the value of the appropriate matching component to be calculated.

If you are interested in this kind of work, start with a primer on RF design.

Complex impedance matching using scalar measurements, math and resistors

Ham Radio Company Wins Big

September 5, 2019 by Al Williams 39 Comments

It is sort of the American dream: start a company in your garage and have it get crazy big. After all, Steve Jobs, Bill Gates, and even Bill Hewlett and Dave Packard did it. Seems hard to do these days, though. However, one ham radio company that has been pushing the edge of software defined radio appears to be well on the way to becoming more than its roots. FlexRadio has teamed with Raytheon to undertake a major project for the United States Air Force.

The Air Force has given Raytheon and FlexRadio $36 million to develop an HF radio based on the existing SmartSDR/Flex-6000. ARRL news reports quote FlexRadio’s CEO as saying that the investment in the military radios will pay dividends to the firm’s ham radio customers.

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