ham radio

243 Articles

Bouncing Radio Off Of Airplanes

December 18, 2015 by 48 Comments

Amateur radio operators are always trying some new stunt or other. It’s like they’ve got something to prove. Take Aircraft scatter for instance: the idea is to extend your radio’s range by bouncing it directionally off of overhead airplanes.

Radio signals travel in straight lines, which is a bummer because the Earth (despite what you’ve heard) is round. Inevitably, if you want to talk to someone far enough away, they’re over a hill. We’ve covered various oddball propagation methods recently, so if you don’t know about moonbounce, you’ve got some background reading to do. But airplane scatter was new to us.

Actually pulling it off requires knowing where the airplanes are, of course. To do so, you could simply look up the aircraft in your target area on the web, using something like FlightRadar24, but where’s the fun in that? There’s also the possibility of tracking local aircraft yourself using RTL-SDR if you’re feeling hard core.

The rest is just details. Hams [Rex Moncur (VK7MO)] and [David Smith (VK3HZ)], for instance, got 10 GHz signals to skip off airplanes over 842 km (PDF). If you’re an old-school ham operator, you’re double-checking the “gigahertz”, but it’s not a mistake. It’s tremendously impressive that these guys got a link over such a long distance using only 10 watts — but note that they’re doing it with highly directive dishes, and telescopes to aim them.

Not to discourage you from trying this at home, but there are all sorts of difficulties that you’ll encounter when you do. Airplanes moving perpendicular to the path between sender and receiver will Doppler-shift the signal, and there’s still quite a chunk of atmosphere to get the signal through. Finally, although airplanes look pretty big when they’re on the ground, they’re actually tiny when they’re up in the sky at 35,000 ft and 500 miles away; you’re bouncing your signal off of a small target.

The good news? People like [W3SZ] are sharing their well-documented results, and at least it’s 20dB easier than bouncing signals off the moon!

Thanks [Martin] for the tip!

Radio Receiver Build Log And More

December 3, 2015 by 8 Comments

At Hackaday, we like to see build logs, and over on Hackaday.io, you can find plenty of them. Sometimes, though, a builder really outdoes themselves with a lot of great detail on a project, and [N6QW’s] Simple-Ceiver project certainly falls into that category. The project logs document many different stages of completeness, and we linked the first one for you as a starting point, but you’ll definitely want to read up to the present. (There were 16 parts, some spanning multiple posts, last time we checked).

It is definitely worth the effort though. The project started out as a direct conversion receiver, but the design goes through and converts it into a superheterodyne receiver. Along the way, [N6QW] shares construction techniques, design advice, and even simulation plots (backed up with actual scope measurements). The local oscillator, of course, uses an Arduino and an AD9850 synthesizer.

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Polyakov Direct Digital Synthesis Receiver

November 15, 2015 by 4 Comments

Direct conversion receivers are popular among ham radio operators and others who build radios. Suppose you want to listen to a signal at 7.1 MHz. With a direct conversion receiver, you’d tune a local oscillator to 7.1 MHz, and mix it with the incoming signal. The resulting sum and differences of the input frequencies will include the audio of an AM signal on the desired frequency.

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RPiTX Turns Rasberry Pi Into Versatile Radio Transmitter

November 4, 2015 by 64 Comments

Since the discovery that some USB TV tuner dongles could be used to monitor radio waves across a huge amount of spectrum, the software-defined radio world has exploded with interest. The one limiting factor, though, has been that the dongles can only receive signals; they can’t transmit them. [Evariste Okcestbon, F5OEO] (if that is his real name! Ok c’est bon = Ok this is good) has written some software that will get you transmitting using SDR with only a Raspberry Pi and a wire.

There have been projects in the past that use a Pi to broadcast radio (PiFM), but this new software (RPiTX) takes it a couple steps further. Using just an appropriately-sized wire connected to one of the GPIO pins, the Raspberry Pi is capable of broadcasting using FM, AM, SSB, SSTV, or FSQ signals. This greatly increases the potential of this simple computer-turned-transmitter and anyone should be able to get a lot of use out of it. In the video demo below the break, [Evariste] records a wireless doorbell signal and then re-transmits it using just the Rasbperry Pi.

The RPiTX code is available on GitHub if you want to try it out. And it should go without saying that you will most likely need an amateur radio license of some sort to use most of these features, depending on your locale. If you don’t have a ham radio license yet, you don’t need one to listen if you want to get started in the world of SDR. But a ham license isn’t hard to get and at this point it shouldn’t take much convincing for you to get transmitting.

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Tiny Radio Tracks Your Balloons

October 28, 2015 by 38 Comments

The name of the game in rocketry or ballooning is weight. The amount of mass that can be removed from one of these high-altitude devices directly impacts how high and how far it can go. Even NASA, which estimates about $10,000 per pound for low-earth orbit, has huge incentives to make lightweight components. And, while the Santa Barbara Hackerspace won’t be getting quite that much altitude, their APRS-enabled balloon/rocket tracker certainly helps cut down on weight.

Tracksoar is a 2″ x .75″ x .5″ board which weighs in at 45 grams with a pair of AA batteries and boasts an ATmega 328P microcontroller with plenty of processing power for its array of on-board sensors. Not to mention everything else you would need like digital I/O, a GPS module, and, of course, the APRS radio which allows it to send data over amateur radio frequencies. The key to all of this is that the APRS module is integrated with the board itself, which saves weight over the conventional method of having a separate APRS module in addition to the microcontroller and sensors.

As far as we can see, this is one of the smallest APRS modules we’ve ever seen. It could certainly be useful for anyone trying to save weight in any high-altitude project. There are a few other APRS projects out there as well but remember: an amateur radio license will almost certainly be required to use any of these.

Why Should You Get A Ham Radio License?

October 23, 2015 by 92 Comments

Several of the authors you read on Hackaday are ham radio operators and we’ve often kicked around having a Hacker Chat about “Why be a ham today?” After all, you can talk to anyone in the world over the Internet or via phone, right? What’s the draw?

The Radio Society of Great Britain had the same thought, apparently, and produced a great video to answer the question. They mention the usual things: learning about technology, learning about people in other parts of the world, disaster communications, and radiosport (which seems to be more popular outside the United States; people compete to find hidden transmitters).

In addition, they talked a lot about how hams get involved with space communications, ranging from talking via satellites, to talking to people on the space station, to actually building small satellites. As the narrator says, there are “hundreds of ways to have techie fun” with ham radio.

One thing we noticed they showed but didn’t say a lot about, though, is the educational opportunities. You can learn a lot, and working with kids to help them learn is often very rewarding (and you usually learn something, too). Just to forestall the comments that this post isn’t hack related, we’ll note two things: there is a Raspberry Pi shown and just past the two-minute mark, there is a very clever hacked together Morse code key.

We talk a lot about ham radio, ranging from Arduino-based digital modes to putting together portable stations (you can see a similar one in the video, too). One other thing we noticed they don’t mention: it is generally much easier to get a license today than ever before. Most countries (including the United States) have abolished the Morse code requirements, so while some hams still enjoy CW (hamspeak for operating Morse code), it isn’t a requirement.

Video below.

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Triple Frequency VFO On A Bamboo Breadboard

October 13, 2015 by 5 Comments

Historically when hams built low power (QRP) transmitters, they’d use a crystal to set the frequency. Years ago, it was common to find crystals in all sorts of radios, including scanners and handheld transceivers. Crystals are very stable and precise and it is relatively easy to make a high quality oscillator with a crystal and a few parts.

The big problem is you can’t change the frequency much without changing crystals. Making a high quality variable frequency oscillator (VFO) out of traditional components is quite a challenge. However, today you have many alternatives ranging from digital synthesis to all-in-one IC solutions that can generate stable signals in a wide range of frequencies.

[N2HTT] likes to build radio projects and he decided to take an Si5351 clock generator and turn it into a three frequency VFO for his projects. The Si5351 uses a crystal, so it is very stable. However, you can digitally convert that crystal frequency into multiple frequencies over a range of about 8kHz to 160MHz.

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