An SSB Transceiver On Only One Type Of Transistor

April 9, 2018 by Jenny List 31 Comments

There are a multiplicity of transmission modes both new and old at the disposal of a radio amateur, but the leader of the pack is still single-sideband or SSB. An SSB transmitter emits the barest minimum of RF spectrum required to reconstitute an audio signal, only half of the mixer product between the audio and the RF carrier, and with the carrier removed. This makes SSB the most efficient of the analog voice modes, but at the expense of a complex piece of circuitry to generate it by analog means. Nevertheless, radio amateurs have produced some elegant designs for SSB transmitters, and this one for the 80m band from [VK3AJG] is a rather nice example even if it isn’t up-to-the-minute. What makes it rather special is that it relies on only one type of device, every one of its transistors is a BC547.

In design terms, it follows the lead set by other simple amateur transmitters, in that it has a 6 MHz crystal filter with a mixer at either end of it that switch roles on transmit or receive. It doesn’t use the bidirectional amplifiers popularised by VU2ESE’s Bitx design, instead, it selects transmit or receive using a set of diode switches. The power amplifier stretches the single-device ethos to the limit, by having multiple BC547s in parallel to deliver about half a watt.

While this transmitter specifies BC547s, it’s fair to say that many other devices could be substituted for this rather aged one. Radio amateurs have a tendency to stick with what they know and cling to obsolete devices, but within the appropriate specs a given bipolar transistor is very similar to any other bipolar transistor. Whatever device you use though, this design is simple enough that you don’t need to be a genius to build one.

Via [G4USP]. Thanks [2ftg] for the tip.

Filter Your Pi And Be A Responsible Pirate

April 3, 2018 by Tom Nardi 20 Comments

At this point it’s pretty well-known that you can tack a long wire to the Raspberry Pi’s GPIO, install some software, and you’ve got yourself the worlds easiest pirate FM radio station. We say that it’s a “pirate” station because, despite being ridiculously easy to do, broadcasting on these frequencies without a license is illegal. Even if you had a license, the Raspberry Pi with a dangling bit of wire will be spewing out all kinds of unintentional noise, making it a no-go for any legitimate purposes.

Unfiltered output of Pi broadcasting on 107.3 MHz

In an effort to address that issue, [Naich] has written up a couple posts on his blog which not only discuss why the Pi is such a poor transmitter, but shows how you can build a filter to help improve the situation. You’ll still be a lawless pirate if you’re transmitting on FM stations with your Pi, but you won’t be a filthy lawless pirate.

In the first post, [Naich] shows us exactly what’s coming out of the wire antenna when the Pi is broadcasting some tunes on the default 107.3 MHz, and it ain’t pretty. The Pi is blasting out signals up and down the spectrum from 50 MHz to 800 MHz, and incredibly, these harmonics are in some cases stronger than the intentional broadcast. Definitely not an ideal transmitter.

[Naich] then goes on to show how you can build a DIY filter “hat” for the Pi that not only cuts down a lot of the undesirable chatter, but even boosts the intended signal a bit. The design is surprisingly simple, only costs a few bucks in components, and conveniently is powered directly from the Pi’s GPIO. It even gives you a proper antenna jack instead of a bare wire wound around a header pin.

We’ve seen plenty of projects utilizing the Raspberry Pi FM transmission hack, and while this mod still doesn’t make it perfect, it’s always nice to see an awesome hack made even better.

Build Your Own Antenna For Outdoor Monitoring With LoRa

March 31, 2018 by Christopher Wang 15 Comments

LoRa and LPWANs (Low Power Wide Area Networks) are all the range (tee-hee!) in wireless these days. LoRa is a sub 1-GHz wireless technology using sophisticated signal processing and modulation techniques to achieve long-range communications.

With that simplified introduction, [Omkar Joglekar] designed his own LoRa node used for outdoor sensor monitoring based on the HopeRF RFM95 LoRa module. It’s housed in an IP68 weatherproof enclosure and features an antenna that was built from scratch using repurposed copper rods. He wrote up the complete build, materials, and description which makes it possible for others to try their hand at putting together their own complete LoRa node for outdoor monitoring applications.

Once it’s built, you can use this simple method to range test your nodes and if you get really good, you might be setting distance records like this.

Simple Decoder Serves As Solo Ham’s Test Buddy

March 31, 2018 by Dan Maloney 11 Comments

For a hobby that’s ostensibly all about reaching out to touch someone, ham radio can often be a lonely activity. Lots of hams build and experiment with radio gear much more than they’re actually on the air, improving their equipment iteratively. The build-test-tweak-repeat cycle can get a little tedious, though, especially when you’re trying to assess signal strength and range and can’t find anyone to give you a report.

To close the loop on field testing, [WhiskeyTangoHotel] threw together a simple ham radio field confirmation unit that’s pretty slick. It relies on the fact that almost every ham radio designed for field use incorporates a DTMF encoder in the microphone or in the transceiver itself. Hams have used Touch Tones for in-band signaling control of their repeaters for decades, and even as newer digital control methods have been introduced, good old analog DTMF hangs in there. The device consists of a DTMF decoder attached to the headphone jack of a cheap handy talkie. When a DTMF tone is received, a NodeMCU connected to the decoder calls an IFTTT job to echo the key to [WTH]’s phone as an SMS message. That makes it easy to drive around and test whether his mobile rig is getting out. And since the receiver side is so portable, there’s a lot of flexibility in how tests can be arranged.

On the fence about ham as a hobby? We don’t blame you. But fun projects like this are the perfect excuse to go get licensed and start experimenting.

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Putting A Poor Man’s Vector Analyzer Through Its Paces

March 29, 2018 by Dan Maloney 20 Comments

If anything about electronics approaches the level of black magic, it’s antenna theory. Entire books dedicated to the subject often merely scratch the surface, and unless you’re a pro with all the expensive test gear needed to visualize what’s happening, the chances are pretty good that your antenna game is more practical than theoretical. Not that there’s anything wrong with that — hams and other RF enthusiasts have been getting by with antennas that work without really understanding why for generations.

But we’re living in the future, and the tools to properly analyze antenna designs are actually now within the means of almost everyone. [Andreas Spiess] recently reviewed one such instrument, the N1201SA vector impedance analyzer, available from the usual overseas sources for less than $150. [Andreas]’s review does not seem to be sponsored, so it seems like we’re getting his unvarnished opinion; spoiler alert, he loves it. And with good reason; while not a full vector network analyzer (VNA) that will blow a multi-thousand dollar hole in your wallet, this instrument looks like an incredible addition to your test suite. The tested unit works from 137 MHz to 2.4 GHz, so it covers the VHF and UHF ham bands as well as LoRa, WiFi, cell, ISM, and more. But of course, [Andreas] doesn’t just review the unit, he also gives us a healthy dose of theory in his approachable style.

[The guy with the Swiss accent] has been doing a lot of great work these days, covering everything from how not to forget your chores to reverse engineering an IoT Geiger counter. Check out his channel — almost everything he does is worth a watch.

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An Introduction To Storm Detector Modules

March 22, 2018 by Sean Boyce 41 Comments

Lightning storm detectors have been around for a surprisingly long time. The early designs consisted of a pair of metal bells and a pendulum. When there was a charge applied, for example by connecting one bell to the ground and the other to a lightning rod, the bells would ring when a lightning storm was close by. In the mid 18^th century, these devices were only practical for demonstration and research purposes, but very likely represent the earliest devices that convert electrostatic charge to mechanical force. A bit over a hundred years later, the first lightning detector was considered by some as the first radio receiver as well.

As soon as I found out about storm detector chips, I knew I would have to get one working. For about $25, I ordered an AMS AS3935 module from China. This chip has been featured before in a number of excellent projects such as Twittering lightning detectors, and networks of Sub-Saharan weather stations. While there’s an Arduino library for interfacing with this IC, I’m going to be connecting it up to an ESP8266 running the NodeMCU firware, which means digging into the datasheet and writing some SPI code. If any of the above tickles your fancy, read on! Continue reading “An Introduction To Storm Detector Modules” →

Icoboard Software Defined Radio Platform

March 20, 2018 by Al Williams 8 Comments

The Icoboard is a plug-in for the Raspberry Pi with a Lattice iCE FPGA onboard. Combined with a cheap A/D converter, [OpenTechLab] build a software-defined radio using all open source tools. He found some inexpensive converters that cost about $25 and were fast enough (32 MHz) for the purpose at hand. The boards also had a digital to analog converter and he was able to find the data sheets. You can see a video with the whole project covered, below.

The video, by the way, is pretty extensive (about an hour’s worth) and covers the creation of a PC board to connect from the Icoboard to the converters. There’s also a 3D printed frame, and that’s explained in detail as well.

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