13.8V 5A power supply

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Dilshan Jayakody published a new build:

13.8V power supplies are commonly used in armature radio experiments. Most of the portable armature radio transceivers are designed to work with a 13.8V power source. We mainly build this power supply unit to power some of our armature radio circuits and modules.
This design is based on the popular LM338 5A voltage regulator. We choose this regulator because of to it’s higher current rating, short-circuit protection feature and higher availability.

See the full post on his blog.

Automated channel switching with Motorola GM3x0

Automated channel switching with Motorola GM3x0

With the integration of POCSAG/DAPNET features into the MMDVM/MMDVMHost I came to think about if it would be possible to combine an MMDVM repeater/HotSpot with a DAPNET tranmitter. The advantage in Germany is that there is a single coordinated frequency for POCSAG tranmissions on UHF. 439.9875MHz is used for fixed-frequency pagers which are modified to receive on that frequency. With latest hand-programmable pagers (e.g. AlphaPoc) it would basically be possible to set them to the repeater frequency but that wouldn’t work while one is en route.
In the programming software for Motorola GM3x0 radios I found an interesting GPIO setting called “Channel Steering”. Some line of the help function revealed that it would exactly do what I expected. You can trigger a GPIO and the radio switches channels.

Via Notizbl0g.

Check out the video after the break.

SI5351 VFO project

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Dave Richards (a.k.a. AA7EE) has a nice write-up about building another Si5351 VFO project:

To many, this will be just another Si5351 VFO project, with nothing to distinguish it from the others. In fact, that’s exactly what it is. The “how to” of connecting an Arduino board to an Si5351 board, wiring up a display, and loading the firmware, is straightforward, and well established. To me though, it was a complete mystery.

See the full post on his blog here.

RX/TX sequencer

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Lukas Fässler has designed and built an RX/TX sequencer based on a PIC16F18325,  that is available on github:

Much like the beacon keyer presented here earlier, this RX/TX sequencer is a simple but useful little device. Its typical use is in ham radio applications when a separate power amplifier (PA) and/or a sensitive low-noise pre-amplifier (LNA) is used. Care has then to be take to safely transition between RX and TX states – and that’s where this sequencer comes in.

Project info at Soldernerd homepage.

Check out the video after the break.

Beacon Keyer

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Lukas Fässler from Soldernerd published a project writeup showing how he built a PIC-based beacon keyer:

This is likely the first ham radio related project that I document here on this blog
But my very first PIC project was a beacon keyer that I made for my father, HB9BBD. That was in 2013. A beacon keyer is a great project to get started with microcontrollers since it’s not much more than a fancy way of blinking an LED.

Project info at Soldernerd homepage and the GitHub repository here.

The Poynting Vector Antenna

Radio amateurs are inventive people, and though not all of them choose to follow it there is a healthy culture of buildng radio equipment among them. In particular the field of antennas is where you’ll find a lot of their work, because the barrier to entry can be as low as the cost of a reel of wire.

Over the years a number of innovative antenna designs have come from radio amateurs’ experimentation, and it’s one of the more recent we’d like to share with you today following a [Southgate ARC] story about a book describing its theory (Here’s an Amazon link to the book itself). The Poynting Vector antenna has been one of those novel designs on the fringes for a while now, it has been variously described as the “Super-T”, or the “flute”. Its party piece is tiny dimensions, a fraction of the size of a conventional dipole, and it achieves that by the interaction between a magnetic field across the plates of a capacitor in a tuned circuit and the electric field between a very short pair of dipole radiators. The trade-off is that it has an extremely high Q and thus a narrow bandwidth, and since its feeder can become part of its resonant circuit it is notoriously difficult to match to a transmitter. [Alan MacDonald, VE3TET] and [Paul Birke, VE3PVB] have a detailed page on the development of their Poynting antenna which takes the reader through the details of its theory and the development of their practical version.

In the roof space above the room in which this is being written there hangs a traditional dipole for the 20m amateur band. Though it is a very effective antenna given that it is made from a couple of pieces of wire and a ferrite core it takes most of the length of the space, and as we’re sure Hackaday readers with callsigns will agree a relatively tiny alternative is always very welcome.

If antennas are a mystery to you then we’d suggest you read an introduction to antenna basics to get you started.


Filed under: radio hacks

Homebrew 40dB step attenuator

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flathagen blogged about his step attenuator build:

A home lab needs a step attenuator. It helps in evaluating RF amplifiers, filters and receivers. Both the legendary EMRFD-book, the ARRL handbook, and a variety of QST-articles provides circuit examples for building a homebrew device. Most of them follow the design principles from the January 1967 edition of the 73 magazine (all editions can be found for free online).
I built my device base on the 73-magazine article, but choose 20 dB, 10 dB, 5 dB, 3 dB and 2 dB sections, giving 40 dB in total. The choice was basically based on the need for about 40 dB total, and the physical limitations in the aluminum box at hand giving room for only 5 pad sections.

Project info at DIYcrap blog.

Get On 10 GHz For 3 Euros

A frequent complaint you will hear about amateur radio is that it is a chequebook pursuit. Of course you can work the incredible DX if you spend $20k on a high-end radio, big antenna, and associated components. The reality is though that because it’s such a multi-faceted world there are many ways into it of which the operator with the shiny rig is taking only one.

On the commonly used HF and VHF bands at the lower end of the radio spectrum you will definitely find chequebook amateurs of the type described in the previous paragraph. But as you ascend into the microwave bands there are no shiny new radios on the market, so even the well-heeled licensee must plow their own furrow and build their own station.

You might think that this would remain a chequebook operation of a different type, as exotic microwave devices are not always cheap. But in fact these bands have a long history of extremely inexpensive construction, in which skilled design and construction as well as clever re-use of components from satellite TV systems and Doppler radar modules play a part. And it is a project following this path that is our subject today, for [Peter Knol, PA1SDB] has repurposed a modern Doppler radar module as a transmitter for the 10GHz or 3cm amateur band (Google Translate version of Dutch original). The best bit about [Peter]’s project is the price: these modules can be had for only three Euros.

Years ago a Doppler module would have used a Gunn diode in a waveguide cavity and small horn, usually with an adjacent mixer diode for receiving. Its modern equivalent uses a transistor oscillator on a PCB, with a dielectric resonator and a set of patch antennas. There is also a simple receiver on board, but since [Peter] is using a converted ten-Euro satellite LNB for that task, it is redundant.

He takes us through the process of adjusting the module’s frequency before showing us how to mount it at the prime focus of a parabolic antenna. FM modulation comes via a very old-fashioned transformer in the power feed. He then looks at fitting an SMA connector and using it for more advanced antenna set-ups, before experimenting with the attenuating properties of different substances. All in all this is a fascinating read if you are interested in simple microwave construction.

The result is not the most accomplished 10 GHz station in the world, but it performs adequately for its extremely low price given that he’s logged a 32 km contact with it.

Though we cover our fair share of amateur radio stories here at Hackaday it’s fair to say we haven’t seen many in the microwave bands. If however you think we’ve been remiss in this area, may we point you to our recent coverage of a microwave radio receiver made from diamond?

Via Southgate ARC.


Filed under: radio hacks

Demystifying Amateur Radio Callsigns

Regular Hackaday readers will be familiar with our convention of putting the name, nickname, or handle of a person in square brackets. We do this to avoid ambiguity as sometimes names and particularly nicknames can take unfamiliar forms that might be confused with other entities referred to in the text. So for example you might see them around [Bart Simpson], or [El Barto]. and occasionally within those brackets you’ll also see a capitalised string of letters and numbers after a name. For example the electronic music pioneer [Bob Moog, K2AMH], which most of you will recognise as an amateur radio callsign.

Every licenced radio amateur is issued one by their country’s radio authority as a unique identifier, think of it as similar to a car licence plate. From within the amateur radio bubble those letters and numbers can convey a significant amount of information about where in the world its user is located, when they received their licence, and even what type of licence they hold, but to outsiders they remain a mysterious and seemingly random string. We’ll now attempt to shed some light on that information, so you too can look at a callsign in a Hackaday piece or anywhere else and have some idea as to its meaning.

[Bob Moog, K2AMH]. PD, via Wikimedia Commons.
[Bob Moog, K2AMH]. PD, via Wikimedia Commons.
Happily for the would-be callsign spotter, there is an internationally agreed format for amateur radio callsigns. It does have occasional edge cases and exceptions, but the chances of encountering them is slim. There will always be a prefix of up to three alphanumeric characters which identifies a country or territory, followed by a single digit, and then followed by up to four characters.

Returning to [Bob Moog]’s callsign [K2AMH] above as a straightforward example, the “K”  is one of the prefix letters A, N, K, and W so far used in the ranges assigned to the USA, the “2” indicates that the callsign was issued in New York or New Jersey because the digit in a US callsign represents a region, and the “AMH” is a sequentially issued string of letters acting as a personal identifier. In more recently issued callsigns this will often be a vanity string, perhaps the operator’s initials or similar.

A seasoned callsign-spotter would also be able to tell you that [Bob Moog]’s callsign originates from sometime in the 1950s, as that was the period in which they started issuing single-letter “K” callsigns, and that it denotes a full or advanced class licence because the “K” is not accompanied by another letter. The FCC provide a handy guide to the callsigns they currently issue, if you are curious.

The Details

[Bob Moog] provides us with our straightforward example above, but as is so often the case there are many exceptions and international differences that mean not all callsign components have the same interpretation. For example in British callsigns the number does not represent a region, instead for the vast majority it conveys the age of the callsign and the class of licence for which it was issued.  If you are digging that deep into the information contained within a callsign issued in another territory, you will often have to resort to your favourite search engine.

[9K2/VO1DZA], a Canadian licencee working 30m WSPR in Kuwait, showing the Kuwaiti prefix in front of the Canadian callsign.
[9K2/VO1DZA], a Canadian licencee working 30m WSPR in Kuwait, showing the Kuwaiti prefix in front of their Canadian callsign.
Sometimes you will see extra letters with a slash at the start and end of a callsign. Letters at the start mean that the station is operating in another country or territory, for example.  Reciprocal agreements exist between countries allowing foreign amateurs to operate within their borders, when doing so they prepend the appropriate international prefix to their own callsign with a slash to indicate the true location of their station. Our example in the image to the left shows a Canadian station working this way in Kuwait.

Of course, not all radio amateurs work from home. There is a long tradition of portable operation, in cars, on foot, in boats, and even in the air. When operating in this manner there is a requirement to indicate this by adding a slash and an appropriate suffix on the end of the callsign. Thus you’ll see “/P” for portable or on foot, “/M” for mobile, and even occasionally “/MM” for maritime mobile and “/AM” for aeronautical mobile. There are tales for example of people working [King Hussein] of Jordan as [JY1/AM] from his royal jet somewhere over the Atlantic on the way to the USA. Incidentally that Jordanian callsign is one of those rare edge cases we mentioned earlier, it has no letters following its number. When you are king, the ultimate in vanity callsigns can be yours!

There is sometimes an undesirable side to being able to extract so much information from a callsign. People will always find an excuse to impose a hierarchy on any group, and radio amateurs are no exception. Thus you will sometimes find holders of older or more advanced licences excluding or being unpleasant to people whose callsigns they deem to be inferior to their own. We recently heard an oldtimer whose callsign reveals he was probably first licenced in the 1950s or 1960s rip into a recently licenced novice with a British M6 callsign, and it was not a particularly pleasant experience. We’re sure Hackaday readers will agree that it doesn’t matter when you were first licenced or what level of radio examination you have passed. You are only as good as the last piece of radio equipment you built, and the last station you worked with it.

We hope this has given you an insight into amateur radio callsigns, and they no longer appear to you as simply random strings when we feature them. If you are interested in amateur radio, you might like to see a previous feature we did on some of the steps required to take your licence exam.

Callsign plate header image: Cody gg 88 [CC BY-SA 4.0], via Wikimedia Commons.


Filed under: Featured, radio hacks

Five-Watt SDR Transciever for Hams

The availability of cheap SDR hardware created a flourishing ecosystem for SDR software, but a lot of the hardware driving the revolution was still “cheap”. In the last few years, we’ve seen quality gear replacing the TV dongles in many setups, and down-converters designed for them to allow them to work on the ham bands.

But something that’s purpose-built might be a better option if ham radio, particularly the shortwave portion thereof, is your goal. First off, you might want to transmit, which none of the TV dongles allow. Then, you might want a bit of power. Finally, if you’re serious about short-wave, you care more about the audio quality than you do immense bandwidth, so you’re going to want some good filters on the receiving end to help you pull the signal out of all the noise.

rs-hfiq_block_diagram_featuredThe RS-HFIQ 5 W SDR transciever might be for you. It’s up on Kickstarter right now, and it’s worth looking at if you want a fully open source (schematics, firmware, and software) shortwave SDR rig. It’s also compatible with various open frontends.

The single-board radio isn’t really a full SDR in our mind — it demodulates the radio signal and sends a 96 kHz IQ signal across to your computer’s soundcard where it gets sampled and fully decoded. The advantage of this is that purpose-built audio rate DACs have comparatively high resolution for the money, but the disadvantage is that you’re limited to 96 kHz of spectrum into the computer. That’s great for voice and code transmissions, but won’t cut it for high-bandwidth data or frequency hopping applications. But that’s a reasonable design tradeoff for a shortwave.

Still, an SDR like this is a far cry from how simple a shortwave radio can be. But if you’re looking to build up your own SDR-based shortwave setup, and you’d like to hack on the controls more than on the radio itself, this looks like a good start.


Filed under: radio hacks