amateur radio

219 Articles

Wind-Up Tape Measure Transformed Into Portable Ham Antenna

March 30, 2022 by 21 Comments

If there’s one thing that amateur radio operators are good at, it’s turning just about anything into an antenna. And hams have a long history of portable operations, too, where they drag a (sometimes) minimalist setup of gear into the woods and set up shop to bag some contacts. Getting the two together, as with this field-portable antenna made from a tape measure, is a double win in any ham’s book.

For [Paul (OM0ET)], this build seems motivated mainly by the portability aspect, and less by the “will it antenna?” challenge. In keeping with that, he chose a 50-meter steel tape measure as the basis of the build. This isn’t one of those retractable tape measures, mind you — just a long strip of flexible metal on a wind-up spool in a plastic case. His idea was to use the tape as the radiator for an end-fed halfwave, or EFHW, antenna, a multiband design that’s a popular option for hams operating from the 80-m band down to the 10-m band. EFHW antennas require an impedance-matching transformer, a miniature version of which [Paul] built and tucked within the tape measure case, along with a BNC connector to connect to the radio and a flying lead to connect to the tape.

Since a half-wave antenna is half the length of the target wavelength, [Paul] cut off the last ten meters of the tape to save a little weight. He also scratched off the coating on the tape at about the 40-meter mark, to make good contact with the alligator clip on the flying lead. The first video below details the build, while the second video shows the antenna under test in the field, where it met all of the initial criteria of portability and ease of deployment.

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Boat Anchor Twins Get A Little Digital Help Staying On Frequency

March 11, 2022 by 9 Comments

In the ham radio trade, gear such as the old Drake units [Dr. Scott M. Baker] has in his radio shack are often referred to as “boat anchors.” It refers to big, heavy radios that were perhaps a bit overengineered compared to the state of the art at the time they were designed, and it’s actually a shame that the name has taken on something of a pejorative connotation, since some of this gear is rock solid half a century or more after it was built.

But older gear is often harder to use, at least compared to the newer radios with microcontrollers and more stable oscillators inside. To make his 1970s-era Drake “Twins” setup of separate but linked receiver and transmitter a little more fun to use, [Scott] came up with this neat Raspberry Pi-based DDS-VFO project to keep his boat anchors afloat. Compared to the original mechanically tuned variable frequency oscillator in the Drake receiver, the direct-digital synthesis method promises more stability, meaning less knob-nudging to stay on frequency.

The hardware used for the DDS-VFO is actually pretty simple — just a Raspberry Pi Zero W driving an AD9850-based signal-generator module. Sending the signal to the Twins was another matter. That was done by tapping into the injection cable linking both units, which meant a few circuit complications to deal with signal attenuation. [Scott] also added amenities like a digital frequency display, optical encoder with crank-style knob to change frequency, and a host of Cherry MX keyswitches for quick access to different features.

From the look of the video below, the Twins are now rock-solid and a lot easier to use. This project is loosely based on a recent panadapter project [Scott] undertook for the receiver side of the Twins.

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S15351 tube transmitter

Retro And New Tech Combine In This Hybrid Ham Transmitter

February 27, 2022 by 9 Comments

We’ve said it before and we’ll say it again: the best part about holding an amateur radio license is that it lets you build and use your own transmitting equipment. Hams have been doing this for more than a century — indeed, it was once the only way to get on the air — using whatever technology was available. But the mix of technologies in this low-power transmitter for the 80-meter band is something you don’t see every day.

As ham [Helge Fykse (LA6NCA)] describes in the video below, the project began when he came into possession of a bonanza of vacuum tubes — 12A6 tetrodes, specifically. The new-old-stock tubes were perfect for an RF power amplifier, but that left the problem of what to use for an oscillator. [Helge] chose to meld the old with the new and used oscillator board that he designed. The board has an ATmega88 microcontroller and an Si5351 oscillator, along with a 3V3 regulator to let the module run on 12 volts. And for a nice retro touch, [Helge] put the board in a 3D printed case that looks like an old-fashioned quartz crystal.

There are some other nice design touches here too. A low-pass filter cleans up the harmonics of the oscillator’s 3.5-MHz square wave output before feeding it to the amplifier, in a nod to proper spectrum hygiene. The primary for the amp’s air-core output transformer is hand-wound, with 3D printed spacers to keep the winding neat and even. The tuning process shown below is interesting, and the transmitter was used to make a solid contact with another ham about 100 km away. And we really liked the look of [Helge]’s shack, stuffed as it is with gear both old and new.

We’ve personally tried the Si5351 for QRP transmitters before, but this blend of the old and new really makes us want to find some tubes and get to playing.

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Work The World On A 555

January 13, 2022 by 14 Comments

Over the years the humble 555 timer has been used in so many unexpected places, but there’s a project from [Frank Latos] which we think may be a first. On a piece of stripboard sit a pair of 555s, and instead of the usual passives there are a set of LC circuits. This is no timer, instead it’s a CW (Morse) transmitter for the 80 metre amateur radio band.

One 555 is configured as a feedback oscillator through a toroidal transformer with a tuned circuit to set the frequency of oscillation. The other takes an inverted input from the oscillator to produce complimentary push-pull outputs from both 555s, which are fed to another transformer that in turn feeds a low-pass filter and thus the antenna.

Free-running squarewave oscillators of this type are not unusual for the lower HF bands, but we think this is the first 555 design we’ve seen. As shown it doesn’t produce much in the way of RF power, but remembering half-decent motor drivers using a 556 dual timer we think that selection of one of the more powerful 555 variants might deliver some more punch. We commend his creativity though, and hope he can get that all-important entry in the log to prove it works.

If you’re curious about low-power radio operation, it’s something we’ve explored before.

Four Band Digital HF SDR Transceiver Offers High Performance For Only $60

December 8, 2021 by 31 Comments

Amateur radio is a hobby that is often thought of as being exclusive to those with a healthy expendable income. In recent years however, the tides have turned. Cheap microcontrollers and signal generators have helped turned things around, and the $60 USD QDX from QRP Labs goes even further by sending the performance/price ratio through the roof. You can see more details in the video below the break.

The QDX is the creation of [Hans Summers] who is well known for producing affordable high performance amateur radio kits that are focused on low power transmission, called “QRP” in ham radio parlance. What is it? It’s a pocket sized four band (80, 40, 30, 20 Meters) software defined radio (SDR) that is designed to be used with some of the most popular digital radio modes: FT8 and JS8Call, as well as any other FSK based mode such as RTTY. It’s also been tested to work well (and within spec) on 60 Meters.

While classic radios have to be connected to a computer through a special hardware interface, the QDX is designed to connect directly to a computer through a standard USB A>B cable. CAT control, PTT, and Audio are all handled directly by the QDX, and no special interface is needed. While the radio is essentially plug and play, configuration, testing, and troubleshooting can be done by connecting to the QDX’s unique serial console, which among other things contains a text based waterfall. For those who want to run their own SDR receiver, I/Q output can be sent directly through the sound card.

Now for the bad news: due to global chip shortages, the QDX is out of stock at the moment, and there’s no telling when they might start shipping again. QRP Labs is looking to source parts wherever they can to get more of the units made, but of course, so is everyone else right now. Continue reading “Four Band Digital HF SDR Transceiver Offers High Performance For Only $60” →

Pete's Simple Seven SSB Transceiver

PSSST! Here’s A Novel SSB Radio Design With Only Seven Transistors

November 20, 2021 by 43 Comments

When [Pete Juliano] sat down to design a sideband transceiver for the 20 Meter (14 MHz) ham radio band, he eschewed the popular circuits that make up so many designs. He forged ahead, building a novel design that he calls Pete’s Simple Seven SSB Transceiver, or PSSST for short.

What makes the PSSST so simple is not only its construction, but the low component count. The same circuit using four 2N2222A’s is used on both transmit and receive. On transmit, an extra three components step in to amplify the microphone input and build output power, which is 2.5-4 Watts, depending on the final output transistor used. The best part is that all of the transistors can be had for under $10 USD! [Pete] shows where radio components such as the RF mixers and the crystal filter can be purchased, saving a new constructor a lot of headaches. The VFO and IF frequencies are both provided by the venerable si5351a with an Arduino at the helm.

Many simple transceivers are designed to demonstrate a minimum viable radio, with performance not really a goal. On the other hand, the PSSST was modeled stage-by-stage in LTSpice, ensuring great transmit audio and nice receiver performance. Be sure to check out the demonstration below the break!

[Pete] has painstakingly documented the entire project on his website, and the code for the VFO is available by request via email. We appreciate this contribution to the homebrew ham radio community, and we’re sure this will provide many nights of solder smoking enjoyment for radio amateurs around the world.

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The Low-Down On Long-Wave: Unlicensed Experimental Radio

October 19, 2021 by 70 Comments

In the 125 years since Marconi made his first radio transmissions, the spectrum has been divvied up into ranges and bands, most of which are reserved for governments and large telecom companies. Amidst all of the corporate greed, the “little guys” managed to carve out their own small corner of the spectrum, with the help of organizations like the American Radio Relay League (ARRL). Since 1914, the ARRL has represented the interests of us amateur radio enthusiasts and helped to protect the bands set aside for amateur use. To actually take advantage of the wonderful opportunity to transmit on these bands, you need a license, issued by the FCC. The licenses really aren’t hard to get, and you should get one, but what if you don’t feel like taking a test? Or if you’re just too impatient?

Well, fear not because there’s some space on the radio spectrum for you, too.

Welcome to the wonderful world of (legal!) unlicensed radio experimentation, where anything goes. Okay, not anything  but the possibilities are wide open. There are a few experimental radio bands, known as LowFER, MedFER, and HiFER where anyone is welcome to play around. And of the three, LowFER seems the most promising. Continue reading “The Low-Down On Long-Wave: Unlicensed Experimental Radio” →