Vintage Transistor powers QRP Transmitter

[Pete Juliano, N6QW] built a 20 M QRP CW transmitter using just a handful of parts. That in itself will not raise any eyebrows, until you find that he built it using one of the very first RF transistors manufactured all the way back in 1955. That’s from before the time most of us were born and not many years after the invention of the transistor in late 1947.

QRP in HAM-speak technically stands for a request to “reduce power” or an offer of “should I reduce power” when appended with a question mark. A QRP transmitter is designed to transmit at really low powers. The accepted upper power limit for QRP transmitters is 5 W, at least for modes like CW using FM or AM modulation. [Pete]’s interest was piqued when he read about a 10 mW 10 M QRP transmitter design in a vintage Radio magazine from the late ’50’s and decided to replicate it. We aren’t sure, but it appears he had a Philco SB-100 RF transistor lying around in his parts bin. The SB-100 was one of the first surface-barrier transistors and could output 10 mW at frequencies up to 30MHz.

[Pete]’s rig was originally putting out 0.4 mW with a 3 V supply, and oscillating at 14.060 MHz in the 20 M band. The design appears to be a simple Colpitts oscillator with just a few parts assembled in dead-bug style on a piece of copper clad laminate. After adding an output transformer, he managed to increase the power output to about 25 mW. Check out [Pete N6QW] sending out a CQ shout out from his QRP transmitter in the video after the break.

If this gets you interested in Amateur Radio, but you are mic-shy, then [Dan Maloney] has some options for you in Shut Up and Say Something: Amateur Radio Digital Modes.

SBF image via Historianbuff CC-BY-SA 3.0, Public Domain
[via Dangerous Prototypes]

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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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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]

Looking Back at QRP Transmitters

When you get to a certain age, you get unsettled by people calling “your” music oldies. That’s how a few of us felt when we saw [Mikrowave1’s] video about Retro QRP – Solid Gold Years (see below). “QRP” is the ham radio term for low power operation, and the “solid gold” years in question are the 1960s to 1980. The videox has some good stuff, including some old books and some analysis of a popular one-transistor design from that time. He even tries a few different period transistors to see which works best.

[Mikrowave1] talks about the construction techniques used in that time frame, old transistors, and some vintage test equipment. You can even see an old ARC-5 command receiver in use to listen to the transmitter. These were made for use in military aircraft and were very common as surplus.

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Ham Goes Nuts for Tiny Transmitter

What’s the minimal BOM for a working amateur radio transmitter? Looks like you can get away with seven parts, or eight if you include the walnut. You’ve got to have a walnut.

Some hams really love the challenge of QRP, or the deliberate use of low-power transmitters to provide a challenge to making long-distance contacts. We’ve covered the world of QRP before and noted that while QRP rigs don’t throw a lot of power, it doesn’t mean that they need to be simple. Some get quite complex and support many different modulation schemes, even digital modes. With only a single 2N3904 transistor,  [Jarno (PA3DMI)]’s tiny transmitter won’t do much more than send Morse using CW modulation, but given that it’s doing so from inside a walnut shell, we have no complaints. The two halves of the shell are hinged together and hold a scrap of perfboard for the simple quartz crystal oscillator. The prototype was tuned outside the shell,  and the 9-volt battery is obviously external, but aside from that it’s nothing but nuts.

We’d love to see [Jarno] add a spring to the hinge and contacts on the shell halves so no keyer is required. Who knows? Castanet-style keying might be all the rage with hams after that.

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LTSpice for Radio Amateurs (and Others)

We don’t think [VK4FFAB] did himself a favor by calling his seven-part LTSpice tutorial LTSpice for Radio Amateurs. Sure, the posts do focus on radio frequency analysis, but these days lots of people are involved in radio work that aren’t necessarily hams.

Either way, if you are interested in simulating RF amplifiers and filters, you ought to check these posts out. Of course, the first few cover simple things like voltage dividers just to get your feet wet. The final part even covers a double-balanced mixer with some transformers, so there’s quite a range of material.

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A Lightweight Two Metre Carbon Fibre Yagi Antenna

If you’ve ever cast your eye towards the rooftops, you’ll be familiar with the Yagi antenna. A dipole radiator with a reflector and a series of passive director elements in front of it, you’ll find them in all fields of radio including in a lot of cases the TV antenna on your rooftop.

In the world of amateur radio they are used extensively, both in fixed and portable situations. One of their most portable uses comes from the amateur satellite community, who at the most basic level use handheld Yagi antennas to manually track passing satellites. As you can imagine, holding up an antenna for the pass of a satellite can be a test for your muscles, so a lot of effort has gone into making Yagis for this application that are as lightweight as possible.

[Tysonpower] has a contribution to the world of lightweight Yagis, he’s taken a conventional design with a PVC boom and updated it with a stronger and lighter boom made from carbon fibre composite pipe. The elements are copper-coated steel welding rods, some inexpensive aluminium clamps came from AliExpress, and all is held together by some 3D-printed parts. As a result the whole unit comes in at a claimed bargain price of under 20 Euros.

This antenna is for the 2 M (144 MHz) amateur band, but since it’s based on the [WB0CMT] “7 dB for 7 bucks”  (PDF) design it should be easily modified for other frequencies. The 3D printed parts can be found on Thingiverse,  and he’s also posted a couple of videos in German. We’ve posted the one showing the build below the break, you can find the other showing the antenna being tested at the link above.

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