Tag Archives: homebrew

SP-2B2C: A video series on the design and construction of a Dual-Band 2 Channel QRP CW rig

My radio projects to this point have typically involved a build and test effort, often spanning 3, 4 or even 6 months, culminating in one long, detailed blog post which was assembled over many months and a video that serves the dual purposes of showing and explaining the rig followed by an outing to one or more SOTA summits.

One consequence of this is that my video and blog output is quite low. Another is the resulting content is long, detailed, and not necessarily accessible to all readers or viewers. The concept/plan/build/test/box up and, finally, demonstrate approach is akin to building a house over a few years and publishing your account upon completion. So much of the story goes untold — old school thinking in 2021.

Concept

I decided to turn this approach around, in the style of Charlie Morris ZL2CTM who (when in homebrewing mode) pumps out an interesting video at least once a week, in which he shares his thoughts, turns over components in his fingers, sketches out circuits and stages, and involves you in a construction story. In fact Charlie went further and invited his subscribers to suggest or vote on candidate projects, which introduces the risk that he will end up with a project that doesn’t work, a situation which I note Charlie is too smart to have fallen in to.

By opening up a homebrew project, or at least by documenting it stage by stage, taking and incorporating feedback along the way, your viewers come on the journey with you, and the outcome emerges as being kind of our achievement rather than my achievement.

There is also a sense that you (the maker) are your viewer’s surrogate maker, which is a worthy thing, given so many would-be makers lack the time, space, experience, tools, eyesight, dexterity, or freedom to complete a homebrew radio project.

2B2C rig in pocket.

Feeding the YouTube video-monster

There is another reason for taking this approach. After a few years on YouTube I started wanting to know more about how the platform works. Or, how to work it. The motivation to ‘catch more subscribers’ is a thought exercise in itself and I won’t go further on it, as it is different for everyone. Suffice to say that when you go to the trouble of making what you think is a good YT video, you naturally want it to be seen by as many people as possible. That in itself seems logical, human, and not crazily narcissistic.

Guidance on catching more YouTube eyeballs is not difficult to find. Useful clues can be found the videos released by YT themselves to creators. Anyone can view these, and there are no secrets, similar advice can be found on many of the thousands of ‘grow your YT channel’ channels. It basically comes down to a bit of commonsense YT Search Engine Optimisation hygiene, and, mixing it up a bit and keeping on with it until you find your niche, then being consistent. Good and engaging content is king (as if we needed to be told that).

One algorithm input is sustained views. How do you get views? Well, you could mine internet memes, or film yourself doing something totally ridiculous or crazy, or take your clothes off, or annoy Police. The options are endless and most have been tried. Almost nobody watches the same great video every day for a month, so the answer isn’t in making a small number of great videos and expecting them to be watched repeatedly.

The majority of YT creators churn out content as best they can, on a regular basis, typically weekly. And new videos get watched, even if only for a few minutes, generating views, and feeding the voracious YT video monster. Video is a consumable medium. The strategy then is to turn out a good video weekly. With all this in mind I resolved to make a video series about the design and construction of a simple but useful QRP CW transceiver, almost as a byproduct. This post kicks off episode 1 and the 8 part series. The complete transceiver design and build story will be published on YouTube as follows:

Part 1 – Concept
Part 2 – Receiver PCB
Part 3 – Receiver Band Pass Filters
Part 4 – Receiver build & test
Part 5 – Tx PCB, keying, pre-driver, LPFs
Part 6 – Transmitter driver
Part 7 – Transmitter PA and tests
Part 8 – Case, finishing and field test.

Other videos on the rig on SOTA and park outings will be added as they occur.

Promoting solder-melting

The other motivation is to share and promote making, or ‘melting solder’. While blogs are an important record and are critical to convey detail, a picture paints a thousand words and moving pictures moreso. The most powerful, pervasive and pervasive medium is undoubtedly video via YouTube, which has become the world’s goto source for content, how-to’s, and entertainment. And in the best of content, all of these elements come together. So, like it or not, video/YT is now the pre-eminent platform for reaching eyeballs at scale, regardless of content type.

Dual-band 2 channel QRP CW transceiver

‘SP-2B2C’ is a project to design, build and document in a video series the design and construction of a two band (40 and 20m) crystal locked (channelised) QRP CW transceiver. The rig is entirely scratch-built, from ‘borrowed’ designs, circuit elements and ideas. It is a compact, neat pocket rig that will provide more than adequate service as a simple parks and portable rig, but it comes into its own for SOTA where the crystal-locked channels will not be a major impediment to making contacts.

Frequency control is provided by separate dedicated and trimmed 7MHz and 14MHz crystal oscillators with buffers and with a fixed transmit offset. The receiver is a conventional Direct Conversion design with strong band pass filtering and an SA612 mixer, followed by a dual op amp for audio filtering and gain, and an LM386 for headphone or speaker listening. It has ample gain both in the shack and on a windy summit.

The transmitter duplicates a parts of the popular QCX and MTR radios using a high speed logic gate as a digital driver, to three BS170 FETs in parallel for a full 5 watts on both bands. Keying for a straight key is done using discrete components. The receiver draws about 50mA and the transmitter up to 0.8A on key down. Band switching is done with two miniature telecom relays.

Sketching the physical and electronic design options.

Schematic

Case

The aluminium sheet and angle case was made to closely match that of a previous rig, SP-X. I wanted these two rigs to look like big brother and little brother. The 2B2C case measures 52mm wide, 105mm long and 32mm high. That’s 2 inches wide, 4 1/4 inches long, and 1 1/4 inches high.

Critique

The videos have plenty of on-air snippets so it is easy to get a sense of performance. They openly address the design and build challenges encountered so I won’t repeat them here, other than to note a few observations on the design that the astute or experienced viewer will notice.

The first is the 40m receiver note — some of the callers come back at around 300 to 500Hz, not the 700Hz that is usual. This is because the transmit offset is done by pulling the crystal low with a diode switched capacitor (around 22pF on 40m). There is also a series C for trimming the crystal (30pF) to the desired frequency, and these two Cs interact. As this trimmer is closed to pull the crystal down, the transmit offset reduces due to the diminishing effect of the 22pF capacitor. The best compromise I could get was to have the oscillator on 7022.3kHz which delivers around 4 to 500Hz transmit pull.

7022.3kHz is an odd frequency. If the caller nets exactly, they sound a 500Hz note. But I suspect some operators call on 7022, and some on 7022.5, so the caller’s CW note is unpredictable. A solution is to go on eBay and buy two 7023 crystals, and parallel these for (hopefully) more swing, and also, a bit more transmit pull. I might do that, because it would be much better to transmit on 7023.0, not 7022.3, and callers should respond consistently on the whole kHz.

The other obvious limitation is the DC receiver bandwidth, which is probably as much as 8kHz wide. That means strong signals can capture the receiver anywhere in this range. The best QSOs are had on a clear band. The crystal-clear tinkling sound of CW on a DC receiver is a delightful thing, but it wears thin in a crowded band.

Apart from these points I am happy with the usability and performance of this simple CW rig, and look forward to trying it on a SOTA activation soon, once COVID lockdowns are lifted, where I think it will shine!

2B2C was spotted at VE6JY on 14060 CW.

Acknowledgments

Thanks go to the authors/designers of the various receiver/transmitter circuit blocks I have copied, in particular, Steve Webber KD1JV, creator of the MTR series, and Hans Summers G0UPL whose QCX is an ongoing inspiration. I’ve used KD1JV bandpass filters, and the same RF driver and PA as is in both these designs.

The keying is from RSGB Homebrew columnist Eamon EI9GQ.

Inspiration is drawn constantly from Hayward, Campbell and Larkins’ Expermiental Methods in RF Design (EMRFD).

Finally the SOTA crowd is a global source of genuine interest and know-how in low power portable radios and their operation, and continues the fine amateur radio tradition of operating minimal QRP radios from the mountains and the fields.

From EMRFD.

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SP-X, a pocket rig for the CW activator in a hurry!

I’ve long been interested in compact and fairly minimal SSB and CW rigs with good performance. I’m not into bells, whistles or menus. Menus are for restaurants! When hiking, walking or bouncing around summits I want to minimise things that are not absolutely necessary, things that can go wrong. Less is more when it comes to a transceiver for portable work.

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Ten Tec Model 1056 DC Receiver – is it any good, and what to do with it?

One of life’s simple pleasures is to rediscover something that bought you engagement and enjoyment in the past. And in COVID lockdown, stuck at home, it’s the perfect time to rummage through boxes in dark corners to sort, throw out, and rediscover old treasures. So it was that I came across this Ten Tec direct conversion receiver board, built around 20 years ago.

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Something old, something new: A four-band 5W/50W SSB/CW transceiver (‘Summit Prowler 7’)

‘Summit Prowler 7’ is my name for this scratch-built multiband SSB and CW transceiver. This rig covers four of the most popular portable, Parks and SOTA bands — 80, 40, 30 and 20m, at a power level of 5 watts, but with an in-built switchable 50 watt power amplifier, so that you have the option to call up the extra power if the going gets rough. The rig weights in at around 1 kilogram or 2.2 pounds, about the same as an FT-817, and is similarly sized. It’s a rig for a wide range of portable situations, and is equally at home on the shack bench.

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Pocket-sized homebrew 40m CW QRPp/QRP transceiver

In May 2019 I activated Mt Dandenong VK3/VC-025 with my latest homebrew rig. It was a CW only activation, five QSOs completed, but while I was handing out 599s, the reports coming back to me from the chasers were well down. Over the next few days on OZSOTA (the VK SOTA discussion group) several chasers made comments to the effect that they could hear other VK3s but nothing much from me. When regulars Tony VK3CAT, Ron VK3AFW and Gerard VK2IO reported the same thing, the evidence for a problem at my end mounted.

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Social distancing project #1: Lightweight Linked Dipole

The coronavirus has stopped just about everything, and is undoubtedly changing our lives forever. With almost every group or event cancelled, there are predictions of mass boredom and social isolation. Many people apparently have no idea what they’ll find to do with their time. How odd. That’s never been a problem for makers like me. So in the interests of the bored and isolated, I offer this story of something useful that can be made in an afternoon — a linked dipole.

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200 watt Class D and Pulse Width Modulated AM Transmitter

This post wraps up a series describing the construction of a 200W Class D AM transmitter for 160m, built, tested and put on air over 6 months from August 2019. The transmitter consists of a digital PLL VFO and driver circuit, an Arduino controller, a microphone amplifier, a Pulse Width Modulator, two H-bridge Class D RF modules each capable of at least 100 watts of carrier, an RF power combiner, Low Pass Filter, a 300W power supply and a switching regulator. At the Australian legal limit of 120W carrier, all parts of the transmitter run cool due the use of switching designs. Previous posts describe the switching regulator, 300 watt DC power supply and dummy loads for this project.

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QRP By The Bay, Chelsea Beach, Melbourne, Saturday 8th February 2020

QRP By The Bay is a regular meet-up of amateur radio operators, makers and experimenters , Chelsea Beach, Melbourne. On Saturday 8th February the weather was summery, a warm 28 degrees C, but windy, 35km/h blow from the south-east. A strong turn out resulted in lots of conversation, show-and-tell, and general story telling. The video shows some of the faces and activity. If you want to know more about any of the people or projects drop a comment below.

I was expecting Peter VK3YE to take his wade-tenna into the shallows for some pedestrian mobile contacts, but the wind made that option risky. No matter, there was plenty to see and discuss at the tables.

Thanks to Peter VK3YE for continuing this series of ‘eyeball’ QSOs, a now regular and much appreciated date on the amateur radio calendar in Melbourne.

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8 Band Superhet AM Receiver

Amplitude Modulation holds a fascination for me. It dates back to those hours spent as a teenager listening to the big broadcast-like amateur AM stations in the 1970s and 80s, on 160, 80 and 40 meters. Signals that seemed as wide and loud as medium wave commercial broadcast stations, bearing sonorous, paced voices that projected a wealth of wisdom and experience, and in many cases, a grandfatherly manner. Back then, AM was known as ‘The Gentleman’s Mode’.

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