Radio Shack Shortwave Goes Digital

May 20, 2020 by Al Williams 26 Comments

If you spent the 1970s obsessively browsing through the Radio Shack catalog, you probably remember the DX-160 shortwave receiver. You might have even had one. The radio looked suspiciously like the less expensive Eico of the same era, but it had that amazing-looking bandspread dial, instead of the Eico’s uncalibrated single turn knob number 1 to 10. Finding an exact frequency was an artful process of using both knobs, but [Frank] decided to refit his with a digital frequency display.

Even if you don’t have a DX-160, the techniques [Frank] uses are pretty applicable to old receivers like this. In this case, the radio is a single conversion superhet with a variable frequency oscillator (VFO), so you need only read that frequency and then add or subtract the IF before display. If you can find a place to tap the VFO without perturbing it too much, you should be able to pull the same stunt.

Continue reading “Radio Shack Shortwave Goes Digital” →

TEMPEST Comes To GNU Radio

May 14, 2020 by Jenny List 10 Comments

As we use our computers, to watch YouTube videos of trucks hitting bridges, to have a Zoom call with our mothers, or even for some of us to write Hackaday articles, we’re unknowingly sharing a lot of what we are doing with the world. The RF emissions from our monitors, keyboards, and other peripherals can be harvested and reconstructed to give a third party a view into your work, and potentially have access to all your darkest secrets. It’s a technique with origins in Government agencies that would no doubt prefer to remain anonymous, but for a while now it has been available to all through the magic of software defined radio. Now it has reached the popular GNU Radio platform, with [Federico La Rocca]’s gr-tempest package.

He describes it as a re-implementation of [Martin Marinov]’s TempestSDR, which has a reputation as not being for the faint-hearted. The current version requires GNU Radio 3.7, but he promises a 3.8-compatible version in the works. A YouTube video that we’ve placed below the break has a range of examples running, though there seems to be little information on the type of antenna employed. Perhaps a log-periodic design would be most appropriate.

Continue reading “TEMPEST Comes To GNU Radio” →

Understanding A Bit About Noise Can Help You Go A Long Way

May 12, 2020 by Jenny List 48 Comments

There are many ways in which one’s youth can be misspent, most of which people wish they’d done when they get older and look back on their own relatively boring formative years. I misspent my youth pulling TV sets out of dumpsters and fixing them or using their parts in my projects. I recognise with hindsight that there might have been a few things I could have done with more street cred, but for me, it was broken TVs. Continue reading “Understanding A Bit About Noise Can Help You Go A Long Way” →

Pulling A Crystal By Grinding It

May 10, 2020 by Jenny List 29 Comments

If you own a radio transmitter, from a $10 Baofeng handheld to a $1000 fancy all-band transceiver, setting the frequency is simply a case of dialing in where you want to go. A phase-locked-loop frequency synthesizer or a software-defined radio will generate your frequency, and away you go. There was a time though when synthesizers were impossibly complex and radio amateurs were faced with a simple choice. Use an LC oscillator and put up with drifting in frequency, or use a crystal oscillator, and be restricted to only the frequencies of the crystals you had. [Mark Erdle, AE2EA] modified a 1950s broadcast AM broadcast transmitter for the 1.8MHz amateur band, and his friend [Andy Flowers, K0SM] thought it needed its crystal back for originality rather than the external frequency source [Mark] had provided. He documents the process of modifying a crystal oven and moving a crystal frequency in the video below the break.

A crystal oven is a unit containing the crystal itself alongside a thermostatic heater, and in this one, the crystal was a 1970s-vintage hermetically sealed HC6 device. He modified the oven to take a socket for older FT243 crystals because the quartz element can easily be accessed. [Andy] picked a crystal as close as he could find below the required frequency. He then ground it down with very fine grit on a glass plate, reducing its mass and thus its resonant frequency. We’re taken through the process of getting it close to frequency, but sadly don’t see the etching that he uses for the very last stage. At the end of the video, we see a QSO on the transmitter itself, which is something of an oddity in an age when AM on amateur bands has been supplanted by other modes for decades.

If you’re curious about the transmitter there’s a video thread following its restoration, and if the guts of older radio gear interests you then take a look at this aircraft receiver lovingly brought back to life.

Continue reading “Pulling A Crystal By Grinding It” →

What Will You Do With An Extra 1.2 Gigahertz?

May 7, 2020 by Jenny List 27 Comments

While our collective minds have been turned towards the global pandemic it’s refreshing to hear that in some quarters life has continued, and events that would have made the news in more normal times have continued to take place while they have been replaced in coverage by more urgent considerations.

In the last few weeks there has been a piece of routine American bureaucracy that flew under the radar but which will have a significant effect on global technology; the United States’ Federal Communication Commission first proposed, then ratified, the allocation of an extra 1200 MHz of spectrum in the 6 GHz band to ISM usage. This allocation process is likely to be repeated by other regions worldwide, freeing up another significant piece of spectrum for unlicensed usage.

In practice this means that there will be a whole new set of WiFi channels created, and we’ll all have a little more spectrum to play around with, so it’s worth examining in a little more detail. Continue reading “What Will You Do With An Extra 1.2 Gigahertz?” →

The Lost Art Of Component Scavenging

May 2, 2020 by Jenny List 115 Comments

With the easy and cheap availability of parts by Internet mail order, it’s easy to forget that acquiring electronic components was once a more tedious process, and it was common to use salvaged parts because they were what you had. Scouring a panel from a dumpster-find TV for the right resistor may now be a thing of the past, but it’s not entirely dead. [Ryan Flowers] was lucky enough to score a box of old CB radios at a garage sale, and takes us through a teardown in search of parts he can use to make a QRP amateur radio rig. Delving into aged electronics is right up our street!

An IF amplifier was high-tech back in '75. — An IF amplifier was high-tech back in ’75.

A possibility for a 27 MHz CB rig is to convert it to the neighbouring 10 m amateur band, but since these were all AM rigs, a mode that sees very little amateur use, it was better to part them out. It’s an interesting study in the evolution of radio design, as an entirely analogue design of mostly discrete components is revealed.

Careful inspection of the photographs reveals a Fairchild uA703 5-transistor IF amplifier chip in a metal can, but that’s about as high-tech as it gets. Unexpectedly there is a huge bank of crystals rather than the frequency synthesiser that would have been standard only a few years later.

He comes away with the chassis, switches and pots, and the RF inductors and crystals from the PCB. Those miniature Toko inductors used to be a common sight, but are now something of a rarity. If you fancy a wallow in semiconductors from this era we’ve previously taken a look at the vintage Fairchild catalogue, in which the uA703 is on page 398.

Building A New RF Remote From Scratch

April 30, 2020 by Tom Nardi 5 Comments

We’ve seen no shortage of projects that use the ESP8266 or ESP32 to add “smart” features to existing home appliances, often by pairing the microcontroller with a radio or IR transmitter. If your device has an existing remote, integrating it into a custom home automation system is often just a matter of getting a few cheap modular components and writing some simple code to glue it all together.

But what if the appliance you want to control doesn’t use a common frequency? That’s a question that [eigma] recently had to answer after finding the remote control for the bedroom ceiling fan was operating at a somewhat unusual 304 MHz. Something like the MAX1472 could probably have been tuned to this frequency, but the chip doesn’t seem to be available in a turn-key module as the popular 315 MHz transmitters are.

There were a few possible options, including using a software defined radio (SDR), but [eigma] didn’t want to spend a fortune on this project or wait months for parts to get shipped from overseas. The most straightforward solution was to design a custom transmitter tuned to the proper frequency using discrete components; something of a dark art to those of us who’ve been spoiled by the high availability of modular components.

What follows is an fascinating look at the design, testing, and troubleshooting of a truly scratch-built transmitter. You won’t find any ICs here, the carrier signal is generated with just a transistor, some carefully measured pieces of wire, and a handful of passive components. By modulating the signal with an ESP32, [eigma] successfully makes the oddball ceiling fan an honorary member of the Internet of Things.

The write-up that [eigma] has done is an absolutely invaluable resource if you ever find yourself in need of rolling a bespoke transmitter. It easily ranks among some of the most informative radio reverse engineering work we’ve covered, and you’d be wise to file this one away for future reference. That said, most of the newer hardware you’re going to run into will probably be utilizing a widely-supported frequency like 433 MHz.