Simple Breadboard SDR For Shortwave

August 26, 2022 by Danie Conradie 20 Comments

One of the best ways to learn about radios is to build your own, even in the age of cheap SDR dongles. [Aniss Oulhaci] demonstrates this with a simple HF SDR receiver built on a breadboard.

The receiver takes the form of a simplified Tayloe detector. An RF preamp circuit amplifies the signal from a shortwave antenna and feeds it into a 74HC4066D analog switch, which acts as a switching mixer. It mixes the input signal with the local oscillator’s I and Q signals to produce the intermediate frequency signals. The local oscillator consists of a SI5351 clock generator with a 74HC74D flip-flop to generate the I and Q pair. The signals pass through a low pass filter stage and get amplified by an LM358 op amp, resulting in the IQ signal pair being fed to a computer’s stereo sound card.

An Arduino is used to control the SI5351 clock generator, which in turn is controlled by the same program created for the SDR Shield. With the audio signal fed to HDSDR, [Aniss] was able to pick up a shortwave radio broadcaster.

While this is by no means a high-performance receiver, building an SDR on a breadboard is still a great weekend project, with plenty of potential for further experimentation.

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Just How Good Is A Tape Measure Antenna Anyway?

August 14, 2022 by Dan Maloney 36 Comments

Amateur radio operators have played a longstanding game of “Will It Antenna?” If there’s something even marginally conductive and remotely resonant, a ham has probably tried to make an antenna out of it. Some of these expedient antennas actually turn out to be surprisingly effective, but as we can see from this in-depth analysis of the characteristics of tape measure antennas, a lot of that is probably down to luck.

At first glance, tape measure antennas seem to have a lot going for them (just for clarification, most tape measure antennas use only the spring steel blade of a tape measure, not the case or retraction mechanism — although we have seen that done.) Tape measures can be rolled up or folded down for storage, and they’ll spring back out when released to form a stiff, mostly self-supporting structure.

But [fvfilippetti] suspected that tape measures might have some electrical drawbacks, thanks to the skin effect. That’s the tendency for current to flow on the outside of a conductor, which at lower frequencies on conductors with a round cross-section turns out to be not a huge problem. But in a thin, rectangular conductor, a little finite element method magnetics (FEMM) analysis revealed that most of the current is carried in very small areas, resulting in high electrical resistance — an order of magnitude greater than a round conductor. Add in the high permittivity of the carbon steel material of the blade, and you end up something more like what [fvfilippetti] calls “a tape measure dummy load.

One possible solution: stripping the paint off the blade and copper plating it. It’s not clear if this was tried; we’d think it would be difficult to accomplish, but not impossible — and surely worth a try.

Remember DAB Radio? The Psion WaveFinder Gets A Teardown

August 13, 2022 by Jenny List 16 Comments

With digital music making a clean sweep in the 1990s over almost all listening media, it’s a surprise to find that there’s one area in which an analog hold-out is still very much alive and kicking. We’re talking not of a vinyl resurgence here but of FM radio, which has managed to effectively hold off its digital competition for a few decades now. Twenty years ago its days seemed numbered though, and in Europe the first generation of DAB digital radios looked ready to conquer the airwaves. Among them was a true oddity and one of Psion’s last significant consumer products, the WaveFinder USB DAB radio receiver. [Backofficeshow] has one, and has given it a teardown for our entertainment. He describes it as the first consumer SDR product which may be a little hyperbolic, but nevertheless, it’s an interesting look at what would become one of computing’s backwaters.

Inside the peak-90s-style translucent blue case is a single PCB with a lot of screening, on which sits a USB controller and a bunch of DSP chips. Radio demodulation was done in hardware, but signal demodulation was apparently done on the host PC. At the time its £299 price made it the affordable end of DAB reception, and The Register opined that its ability to download broadcast broadband data made it a revolutionary product, but sadly neither consumers nor broadcasters agreed and it was heavily discounted before making an ignominious exit. DAB itself would struggle to meet the expectations, and a multiplex-based licensing model for broadcasters making it unattractive to local stations means that even now FM is still full of stations. Perhaps as listening moves inexorably to streaming its time has passed, indeed Ireland has gone so far as to abandon DAB altogether.

If you’d like to know more about DAB, we took a look at the technology a while back.

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Testing Antennas With WSPR

July 29, 2022 by Al Williams 19 Comments

There are many ways to test HF antennas ranging from simulation to various antenna analyzers and bridges. However, nothing can replace simply using the antenna to see how it works. Just as — supposedly — the bumblebee can’t fly, but it does so anyway, it is possible to load up some bed springs and make contacts. But it used to be difficult — although fun — to gather a lot of empirical data about antenna performance. Now you can do it all with WSPR and [TechMinds] suggests a moderately-priced dedicated WSPR transmitter to do the job. You can see a video about the results of this technique below.

While WSPR is often cited as taking the fun out of ham radio, it is perfect for this application. Connect the transmitter and a few hours later, visit a web page and find out where you’ve been heard by an objective observer. If you had a few of these, you could even examine several antennas at similar times and conditions.

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Reverse Engineering A Phased Array System Reveals Surprising Details

July 21, 2022 by Ryan Flowers 13 Comments

The term “phased array” has been around for a long time, but in recent years we’ve heard more and more about the beam shaping that’s possible with phased array antennae. In the video below the break, [The Signal Path] breaks down a Qualcomm 60GHz WiGig unit, and does a deep dive, even looking at the bare silicon and an x-ray of an antenna.

An X-Ray of the antenna shows the intricate design

Some fascinating highlights include how not only the data signal is sent to the antennae through a standard coaxial cable, but so are control signals and a base clock frequency. [The Signal Path] explains how the manufacturer chose to use what’s called a SuperHeterodyne (aka “superhet”) architecture, which is not all that different from those used in traditional amateur radio transceivers. In theory, anyway.

Another element that is discussed is how the PCB’s themselves are used as waveguides, inductors, and transmission line matches, among other countless little hacks to fit a rather complex system into a truly diminutive space.

If you’re not familiar the concept behind phased arrays, check out this article we published in 2019 that shows how phased arrays can steer a beam without any moving parts. It’s quite fascinating!

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Beautiful Inductors, Now Not Such A Lost Art

July 17, 2022 by Jenny List 12 Comments

As ferrite technology has progressed into a mastery of magnetic permeability, the size of inductors has gone down to the point at which they are now fairly nondescript components. There was a time though when inductors could be beautiful creations of interleaving layers of copper wire in large air-cored inductors, achieved through clever winding techniques. It’s something that’s attracted the attention of [Brett], who’s produced a machine capable of producing something close to the originals.

Part of the write-up is an investigation of the history, these coils were once present even at the consumer level but are now the preserve of only a few highly secretive companies. They are still worth pursuing though because they can deliver the high “Q” factor that is demanded in a high quality tuned circuit. The rest of the write-up dives in detail into the design of the wire feeder, and the Arduino motor control of the project. There should be enough there for any other experimenters to try their hands at layered inductors, so perhaps we’ll see this lost art make a comeback.

Custom coils are a regular requirement for anything from radios, to musical instruments, to switching power supplies, so it’s not surprising that quite a few projects featuring them have made it here. One of the more unusual of late has been one that winds toroids.

Impatience Is A Virtue When Testing This Old Maritime Teleprinter

July 16, 2022 by Dan Maloney 1 Comment

[Larry Wall], inventor of Perl, once famously said that programmers have three key virtues: sloth, hubris, and impatience. It’s safe to say that these personality quirks are also present in some measure in most hardware hackers, too, with impatience being perhaps the prime driver of great hacks. Life’s too short to wait for someone else to build it, whatever it may be.

Impatience certainly came into play for [Sebastian (AI5GW)] while hacking a NAVTEX receiver (in German). The NAVTEX system allows ships at sea to receive text broadcast alerts for things like changes in the weather or hazards to navigation. The trouble is, each NAVTEX station only transmits once every four hours, making tests of the teleprinter impractical. So [Sebastian]’s solution was to essentially create his own NAVTEX transmitter.

Job one was to understand the NAVTEX protocol, which is a 100-baud, FSK-modulated signal with characters encoded in CCIR 476. Since this encoding is also used in amateur radio teletype operations, [Sebastian] figured there would surely be an Arduino library for encoding and decoding it. Surprisingly, there wasn’t, but there is now, allowing an Arduino to produce the correct sequence of pulses for a CCIR 476-encoded message. Fed into a function generator, the mini-NAVTEX station’s signal was easily received and recorded by the painfully slow teleprinter. There’s that impatience again.

We thought this was a neat hack, and we especially appreciate that [Sebastian]’s efforts resulted in a library that could be useful to hams and other radio enthusiasts in the future. We’ve talked about some more modern amateur radio digital modes, like WSPR and FT8, but maybe it’s time to look at some other modes, too.

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