Shut Up and Say Something: Amateur Radio Digital Modes

In a recent article, I lamented my distaste for carrying on the classic amateur radio conversation — calling CQ, having someone from far away or around the block call back, exchange call signs and signal reports and perhaps a few pleasantries. I think the idle chit-chat is a big turn-off to a lot of folks who would otherwise be interested in the World’s Greatest Hobby™, but thankfully there are plenty of ways for the mic-shy to get on the air. So as a public service I’d like to go over some of the many digital modes amateur radio offers as a way to avoid talking while still communicating.

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See Satellites with a Simple Radio Telescope

Have you got a spare Dish Network antenna lying about? They’re not too hard to come by, either curbside on bulk waste day or perhaps even on Freecycle. If you can lay hands on one, you might want to try this fun radio telescope build.

Now, don’t expect much from [Justin]’s minimalist build. After all, you’ll be starting with a rather small dish and an LNB for the Ku band, so you won’t be doing serious radio astronomy. In fact, the BOM doesn’t include a fancy receiver  – just a hacked satellite finder. The idea is to just get a reading of the relative “brightness” of a radio source without trying to demodulate the signal. To that end, the signal driving the piezo buzzer in the sat finder is fed into an Arduino through a preamp. The Arduino also controls stepper motors for the dish’s azimuth and elevation control, which lets it sweep the sky and build up a map of signal intensity. The result is a clear band of bright spots representing the geosynchronous satellites visible from [Justin]’s location in Brazil.

Modifications are definitely on the docket for [Justin], including better equipment that will allow him to image the galactic center. There may be some pointers for him in our coverage of a tiny SDR-based radio telescope, or from this custom receiver that can listen to Jupiter.

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[Ashhar Farhan]’s done it again!

If you are a regular follower of these pages as well as a radio amateur, you may well have heard of [Ashhar Farhan, VU2ESE]. He is the designer of the BitX, a simple single-sideband transceiver that could be built for a very small outlay taking many of its components from a well-stocked junk box.

In the years since the BitX’s debut there have been many enhancements and refinements to the original, and it has become something of a standard. But it’s always been a single-band rig, never competing with expensive commercial boxes that cover the whole of the available allocations.

With his latest design, he’s changed all that. The uBITX (Micro-BITX when spoken aloud), is an SSB and CW transceiver that covers all of the HF amateur bands, and like the original is designed for the home constructor on a budget. It shows its heritage in the use of bi-directional amplifiers, but diverges from the original with a 45 MHz first IF and an Arduino/SI5351 clock generator in the place of a VFO. It looks to be an excellent design in the spirit of the original, and we can’t wait to see them in the wild.

He’s put up a YouTube video which we’ve placed below the break. His write-up is extensive and fascinating, but it is his closing remarks which sum up the project and the reason why you should build one. We don’t often reproduce entire blocks of text, but this one says it so well:

As a fresh radio amateur in the 80s, one looked at the complex multiband radios of the day with awe. I remember seeing the Atlas 210x, the Icom 720 and Signal One radios in various friends’ shacks. It was entirely out of one’s realm to imagine building such a general coverage transceiver in the home lab.

Devices are now available readily across the globe through online stores, manufacturers are more forthcoming with their data. Most importantly, online communities like the EMRFD’s Yahoo group, the BITX20’s community etc have placed the tribal knowledge within the grasp of far flung builders like I am.

One knows that it was just a matter of breaking down everything into amplifiers, filters, mixers and oscillators, but that is just theory. The practice of bringing a radio to life is a perpetual ambition. The first signal that the sputters through ether, past your mess of wires into your ears and the first signal that leaps out into the space from your hand is stuff of subliminal beauty that is the rare preserve of the homebrewer alone.

At a recent eyeball meet, our friend [Dev(VU2DEV)] the famous homebrewer said “Now is the best time to be a homebrewer”. I couldn’t disagree.

If you build a uBITX, please share it with us!

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Backscatter Your Own FM Pirate Radio Station

If you live in a city, you’re constantly swimming in a thick soup of radio-frequency energy. FM radio stations put out hundreds of kilowatts each into the air. Students at the University of Washington, [Anran Wang] and [Vikram Iyer], asked themselves if they could harness this background radiation to transmit their own FM radio station, if only locally. The answer was an amazing yes.

The trailer video, embedded below, demos a couple of potential applications, but the paper (PDF) has more detail for the interested. Basically, they turn on and off an absorbing antenna at a frequency that’s picked so that it modulates a strong FM signal up to another adjacent channel. Frequency-modulating this backscatter carrier frequency adds audio (or data) to the product station.

One of the cooler tricks that they pull off with this system is to inject a second (stereo) channel into a mono FM station. Since FM radio is broadcast as a mono signal, with a left-minus-right signal sent alongside, they can make a two-channel stereo station by recreating the stereo pilot carrier and then adding in their own difference channel. Pretty slick. Of course, they could send data using this technique as well.

Why do this? A small radio station using backscatter doesn’t have to spend its power budget on the carrier. Instead, the device can operate on microwatts. Granted, it’s only for a few feet in any given direction, but the station broadcasts to existing FM radios, rather than requiring the purchase of an RFID reader or similar device. It’s a great hack that piggybacks on existing infrastructure in two ways. If this seems vaguely familiar, here’s a similar idea out of the very same lab that’s pulling off essentially the same trick indoors with WiFi signals.

So who’s up for local reflected pirate radio stations?

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Move Over Baofeng, Xiaomi Want To Steal Your Thunder

To a radio amateur who received their licence decades ago there is a slightly surreal nature to today’s handheld radios. A handheld radio should cost a few hundred dollars, or such was the situation until the arrival of very cheap Chinese radios in the last few years.

The $20 Baofeng or similar dual-bander has become a staple of amateur radio. They’re so cheap, you just buy one because you can, you may rarely use it but for $20 it doesn’t matter. Most radio amateurs will have one lying around, and many newly licensed amateurs will make their first contacts on one. They’re not even the cheapest option either, if you don’t mind the absence of an LCD being limited to UHF only, then the going rate drops to about $10.

The Baofengs and their ilk are great radios for the price, but they’re not great radios. The transmitter side can radiate a few too many harmonics, and the receivers aren’t the narrowest bandwidth or the sharpest of hearing. Perhaps some competition in the market will cause an upping of the ante, and that looks to be coming from Xiaomi, the Chinese smartphone manufacturer. Their Mijia dual-band walkie-talkie product aims straight for the Baofeng’s jugular at only $35, and comes in a much sleeker and more contemporary package as you might expect from a company with a consumer mobile phone heritage. Many radio amateurs are not known for being dedicated followers of fashion, but for some operators the sleek casing of the Mijia will be a lot more convenient than the slightly more chunky Baofeng.

This class of radio offers more to the hardware hacker than just an off-the-shelf radio product, at only a few tens of dollars they become almost a throwaway development system for the radio hacker. We’ve seen interesting things done with the Baofengs, and we look forward to seeing inside the Xiaomi.

We brought you a look at the spurious emissions of this class of radio last year, and an interesting project with a Baofeng using GNU Radio in a slightly different sense to its usual SDR function.

[via Southgate ARC]

Adding an External Antenna to the Raspberry Pi Zero W

Putting a complete WiFi subsystems on a single-board computer is no mean feat, and on as compact a board as the Zero W, it’s quite an achievement. The antenna is the tricky part, since there’s only so much you can do with copper traces.

The new Raspberry Pi Zero W’s antenna is pretty innovative, but sometimes you need an external antenna to reach out and touch someone. Luckily, adding an external antenna to the Zero W isn’t that tough at all, as [Brian Dorey] shows us. The Pi Zero W’s designers thoughtfully included solder pads for an ultra-miniature surface-mount UHF jack. The jack pads are placed very close to the long, curving trace that acts as a feedline to the onboard antenna. There’s even a zero ohm SMT resistor that could be repositioned slightly to feed RF to the UHF jack. A little work with a soldering iron and [Brian]’s Pi was connected to an external antenna.

[Brian] includes test data, but aside from a few outliers, the external antenna doesn’t seem to offer a huge advantage, at least under his test conditions. This speaks to the innovative design of the antenna, which [Roger Thornton] from the Raspberry Pi Foundation discussed during last week’s last week’s Hack Chat. Check out the archive for that and more.

Thanks to [theEngineer] for the tip.

Antenna Analyzer is a Lab in a Box

There was a time when the measure of a transmitting radio antenna was having it light an incandescent bulb. A step up was a classic SWR/Power meter that showed you forward and reflected power. Over the years, a few other instruments have tried to provide a deeper look into antenna performance. However, the modern champion is the antenna analyzer which is a way of measuring vector impedance.

[Captain Science] did a review of an inexpensive N1201SA analyzer. This device is well under $200 from the usual Chinese sellers. The only thing a bit odd is the frequency range which is 140 MHz to 2700 MHz. For some extra money (about $80 or $100 more) you can drop the low-end frequency to just under 35 MHz.

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