Category Archives: homebrew

Saving an Arduino-controlled DDS VFO frequency over a power cycle

Following the success of My First DDS VFO, complete with Arduino script programming, I found myself interested in mimicking more of the features of the digital dials in ‘real’ rigs. Like dynamic incremental speed-tuning, where the tuning rate increases or decreases dynamically depending on how fast you spin the dial. More on this later. A more achievable feature is to have the band, mode and VFO come up on the frequency where you left it at the last power-down. This involves writing these parameters into the Arduino’s EEPROM, using the EEPROM library.

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QRP by the Bay 4th Feb 2017

QRP by the Bay for February 2017 was held on a blistering 36 degree day at Victory Park, Chelsea Beach. As I approached it looked like about 2,000 people had come to QRP by the Bay, and many of them dragging beach umbrellas and esky’s. Looked like a ripper of a summer QRP party. Parking the car took me 15 minutes. I wondered what Peter Parker had done to pull such an impressive crowd. Alas, when I got to the hallowed tables, there were about a dozen of us, the other 1,988 people having walked blissfully past the squid pole and BITX rigs for the golden sands and cooling waters of Chelsea Beach. Their loss.

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Yet another Arduino Nano and si5351 DDS VFO/BFO

The second weekend in January 2017 afforded time to build something I’ve been wanting to build for several years, my first DDS VFO. I’ve built a kit DDS VFO with pre-soldered surface mount parts and burned-in firmware, but this was to be a scratch build with Arduino Nano, Arduino/C code with modifications, and a Silicon Labs si5351 on a breakout board. I used the wiring map and script from Tom AK2B. It is modified from one by SQ9NJE and uses Jason NT7S si5351 library. The script is elegantly simple, supporting a single push-button to cycle frequency increments, and dealing with encoder interrupts, contact debouncing, refreshing the LCD display, IF offset and VFO/BFO outputs. At the code level Jason’s si5351 library hides the gutsy device interfacing, giving you just a handful of common-sense functions to call… for example, set_frequency() takes as its argument the frequency in centi-hertz (1/100th of a hertz) and the ‘clock 0/1/2’ flag. It couldn’t be simpler. The Adafruit board contains the si5351 and a 25MHz clock (from local IoT supplier Core Electronics).  I chose Veroboard as the substrate for the controller proper, and it proved suitable. Here’s a video demonstration of the VFO’s features.

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Mt Nelse (VK3/VE-004) first attempt: Or, how to blow an IRF510 on a 10 point summit

Day 3 of the Australia Day long weekend (Saturday 28th) was to be a 30 point day up on the summits of the Bogong High Plains, not far south of Falls Creek, starting with Mt Nelse (VK3/VE-004), Mt Cope (VG-001) and Mt McKay (VE-007). I chose Mt Nelse, a 5km walk each way, to start the day, parking at the second sign and car park after Rocky Valley Dam (first Heathy Spur, then Watchbed Creek).  The walk up is easy over rolling hill-like grades. After passing Marum Point track on the right, then Johnson’s and Edmonson hut turnoffs, the summit came up on the right, about 300m off the track. At the top the wind was buffeting. I found a threesome of hikers eating their lunch in the leeward side of the cairn which provided some limited shelter. These three mid-age walkers had met at Bogong summit 30 years ago and had got together for a high country walking weekend nearly every year since. It was their 30th anniversary walk this year.

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A scratch-built 30m CW transceiver (Wilderness SST 30)

The Wilderness SST was designed around 1997 by Wayne Burdick, N6KR of Elecraft fame.  It was kitted (by Wilderness Radio) and sold well to excellent reviews.  On eHam the rig scores 5.0/5 from 33 reviews.  It is an exercise in minimalist design, and there is obvious lineage to be seen in how certain aspects of the SST design found their way into the Wilderness range of QRP radios, such as the way the receiver is coupled to the PA output and monitors the transmitted signal, and the audio-derived AGC.  It was respected among the QRP crowd in the USA (it appears in a list of QRP kits on Wikipedia, most of which are from US sources) but was not widely known here in VK. Fortunately, all of the resources and more to build this transceiver are easily found online.

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QRP by the Bay, Saturday 5th November 2016

QRP by the Bay is a regular homebrew, experimenter’s and portable ops show-and-tell hosted by Peter VK3YE at Chelsea Beach. This was my second event, which followed in the now established tradition.  This year it attracted about two dozen people and a variety of projects appeared on the tables. The weather was not ideal, it was very windy and cool, but the squid poles went up nonetheless.  Peter’s video of the event is here, and another one of the 160 meter bayside portable QSO here.

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‘Summit Prowler One’: A homebrew 7MHz SSB QRP transceiver for SOTA

It all started 18 months ago with the completion of the MST400, a 7MHz SSB QRP transceiver in kit form. I’ve used this 40 meter 5 watt monobander for 34 SOTA activations to date.  It is the radio that appears in every one of my activations in this blog till this weekend. Following the pleasing performance of the MST receiver I wanted to scratch-build an SA612 based radio, to see if I could reproduce the performance of the MST400 but with a few changes to make it even better for activations.  I christened this radio the ‘Summit Prowler One’.  Summit Prowler?  Last year my First Harmonic and friends went through a huge ‘Magic The Gathering‘ stage.  MTG is a mythical strategy card game full of weird characters with strange powers.  When I first saw the MTG Summit Prowler card it occurred to me that there was a link to SOTA there, somewhere.  First Harmonic has moved on to other games, but my first Summit Prowler has been born!  Here it is, in its first incarnation, on the bench, around May 2016.

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Mt Little Joe (VK3/VC-027) and Mt Strickland (VK3/VN-030)

Sunday 23rd October 2016 promised to break a cold and wet spell in Victoria’s Spring weather that had deposited heavy rain, hail and snow down to 800 meters.  The night before, a bunch of keen activators had braved the weather to participate in a VK-ZL-G-Eu joint activation timed to capitalise on grey-line propagation.  Hats off to those who did go out because Melbourne’s weather was atrocious and a summit was about the last place most people would have wanted to be.  The next day, Sunday, dawned dry.  I considered going up to Lake Mountain for Federation Range but the snow cams showed a fresh coating of powdery white stuff, not enough to ski on but plenty enough to make it cold. What I really wanted was to christen my recently completed homebrew 7MHz SSB rig, codenamed ‘Summit Prowler One’.  The design and build story for this project in another post.  Mt Little Joe promised a good activation experience and a fresh mountain walk.

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Superhet crystal mixing schemes

Homebrew superheterodyne receivers/transceivers using a computer crystal ladder filter, BFO and  VXO offer the combination of simplicity and stability.  The key to this receiver pattern is the VXO.  I know VXOs are so ’90s, and that I should embrace digital and start banging out DDS VFOs with Arduinos, eBay AD9850 cards and AdaFruit si5351‘s.  I will soon, I promise.  In the mean time I just want to explore computer crystal mixing schemes a little longer.   Scratch-building a DDS VFO necessitates some new practices, such as getting the script you’ve picked from dozens online to compile and download to the controller, for the particular combination of display, Arduino and DDS chip in use.  I’m not saying it’s too difficult, I’m just observing that it isn’t trivial, and if you get stuck you may find yourself limited in your options to unpick it.  Crystals, on the other hand, are real, physical things, remarkable for their sharp resonant characteristics.  And these days they’re almost literally a dime a dozen.

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2.4GHz Wifi corner reflector 

First Harmonic (FH) was getting patchy wifi coverage to his desktop computer in his bedroom.  The obvious thing would be to invest in a new multiband wifi modem/router, one of those things that looks like a UFO with spiky antennas for its multiple bands.  But the situation presented a good opportunity for some basic UHF antenna experiments over this short unlicensed duplex data link. Discussion of the popular Cantenna suggested lower performance than many have claimed due to the small size of Pringles/Milo cans at 2.4GHz. A repurposed satellite TV dish of diameter 1.2m or more seems to be the best option.  Not having one, and needing a solution that would not turn FH’s bedroom into a junkyard, I opted for a homebrew corner reflector based on one of the many online designs.

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