Category Archives: maker

Arduino GPS experiment for SOTA

How could a GPS unit integrated with a SOTA transceiver assist in activations? I’ve been turning that thought over for a while now after seeing David VK5KK’s GPS and Arduino based grid square locator (posted to the ‘VK Homebrew’ group on facebook).   The ready availability of cheap GPS units with a simple serial interface makes the option straight-forward.  As my homebrew rigs are using Arduino Nanos and si5351 breakout boards, the GPS is just another (serial) attachment.

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Hard-to-find faults and other homebrew ‘Gumption traps’

I recently cut this small piece Veroboard to hold two vertically aligned miniature potentiometers on a receiver front panel. The three soldered tracks to the right allow connection of the audio signal to the volume control using shielded twin conductor cable. Very standard stuff, I’ve been wiring up audio amplifiers to volume controls like this for about four decades. But this one wouldn’t work. It has a fault — it’s there, in the picture above, right in front of your eyes… can you see it?

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‘Summit Prowler IV’ — Homebrew 160m to 17m QRP SSB/CW transceiver for portable and SOTA use

‘Summit Prowler IV’ is a scratch-built six-band SSB and CW transceiver, designed for portable and SOTA activations. It is based on Leon VK2DOB’s MST3 (Minimal Sideband Transceiver, third version) from 2016, with alterations to support multiple bands, my Arduino-based digital VFO/controller and keyer, and a few extras to support portable operating. The transceiver is a conventional single-conversion superhet with 12MHz IF and an si5351 and Arduino Nano-based digital VFO. This project comes after having done more than 50 activations with my 2013 MST Mk I kit radio on 40m SSB. This rig has performed well on 40m SSB (and CW after I added it) and has launched my interest in SOTA activating, turning me into an occasional weekend ‘summit prowler‘.

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Veroboard at radio frequencies

Charlie ZL2CTM has been pushing out a series of excellent videos on his YouTube channel that take you through the circuit design, making and testing of superhet SSB transceiver modules.  Yesterday my eyebrow involuntarily raised ever so slightly at his use of Veroboard as the substrate for his latest 8MHz crystal filter.  Veroboard? At radio frequencies?  Veroboard et les fréquences radio ne sont pas compatibles!

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QRP By The Bay, Chelsea Beach, Melbourne, 25 Nov 2017

QRP By The Bay for November 2017 brought together many familiar and a few new faces and callsigns on an unseasonably hot 32 degree Celsius day. When Peter VK3YE wrapped himself up with radios and aerial parts including an ankle clasp that looked straight out of a Monty Python costume department a small crowd followed him over the dunes and down into the shallows. It was the best place to be on a hot afternoon, toes in the clear and cooling waters of Port Philip Bay.  Or should I say, VK3YE’s State-sized ground plane. The now sub surface mannacle paid off for its wearer.  Forty and 10m contacts rolled in while a few of us chatted at the edge.

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An SSB receiver from an Arduino/si5351 VFO/BFO

Having finished my latest Arduino Nano/si5351 VFO/BFO/Controller, I wanted to hook it up to some receiver stages to realise a SSB receiver. My grand plan for these modules is to build a multiband SSB/CW transceiver for SOTA and portable operation (another rig in my established ‘Summit Prowler’ series). The architecture will be a single conversion superhet with an IF of 12 MHz. For a base design I chose Leon VK2DOB’s MST3, a proven design which I am very familiar with, having used the MST (circa 2013) on nearly all of my SOTA activations to date.

I scratch-built two boards. The first is the MST3 product detector (SA612), audio filter (NE5534) and audio amplifier (TDA7052A). This module includes receiver muting, sidetone injection and audio-derived AGC which controls the gain of the TDA7052A. The second board contains the transmit and receive mixers (both SA612s), some SA630D RF switches to switch the bandpass filter between transmit and receive signal paths, as well as two 5-pole crystal filters (one for SSB, one for CW), each switched by another pair of SA630Ds. There is no IF gain stage, although I put some pads on the end of this board for one or two MOSFET stages, if needed.

As per other recent scratch building efforts these boards are a curious jumble of thru-hole and SOIC ICs, soldered to the copper side of a Muppet style hand drawn and etched board, largely populated with junk box and surplus sales components.

Once the boards were debugged, temporarily adding a 40m bandpass filter and connecting the VFO/BFO up brought the little receiver to life. I used no si5351 clock filtering or buffering, just CLK0 and CLK2 square waves straight into the SA612 Gilbert cell active mixers, which have some useful gain. The sound of the receiver is pleasant, to me at least. The video includes a range of DX and local signals on 40m from my QTH in the north-eastern suburbs of Melbourne, received over a day.
Next, I will add a third board with a bank of switched bandpass filters and switching logic, all controlled by the Arduino. More to follow.

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My second homebrew Arduino/si5351 Digital VFO-Controller

Back in February 2017 I scratch-built my first Arduino and si5351 VFO. Here’s my second one. It is a generic Nano/si5351 module wired up to Farhan’s Raduino circuit. The si5351 is on an Adafruit breakout which includes a 3.3v regulator and crystal. Everything else is as per Raduino other than the presence of a second 7805 regulator for the LCD (and a 1000uF electrolytic storage capacitor) which will allow testing of Pavel CO7WT’s scheme for saving the VFO frequency to the Arduino’s EEPROM when the power drops.

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DIYODE Issue 1 July 2017

DIYode, a new Australian DIY electronics magazine has just launched. I picked up my first edition from the Jaycar counter. It’s thick, glossy and oozes high production values. There’s an nostalgia in having a current electronics magazine on the coffee table. It takes me back to the 1980s when Electronics Australia, Silicon Chip and Electronics Today International bought circuits, components, kits and articles, not to mention ads and specials from hobbyist-focused advertisers like Dick Smith into our lives every few weeks.  Those days are gone forever.  Smartphones and the internet have put every circuit diagram and datasheet at our fingertips, and have spawned global communities which put world experts just minutes or hours away.  So in July 2017, where does a glossy DIY electronics magazine fit in this smorgasbord of information and community?

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1977 digital clock kit retrospective 

I recently came across a small electronic treasure from my youth. It is a digital clock kit, circa 1977. This was the first electronics kit I ever bought and built. It might have been bought from Dick Smith Electronics although there is no DSE branding — that may have come later.  I think it cost in the order of $25. I remember it being pricey enough that I had to put a few dollars aside for a while until I had enough.

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Homebrew 40m SSB rig gets CW, keyer, break-in, AGC and metering

A couple of ‘solder sessions’ finished all the wiring, debugging and testing required to deploy my Arduino Nano keyer and SWR/power meter, and the LED LDR AGC and S-meter modules into my homebrew 40 meter SSB rig (MST Mk1 from OzQrp).  Before reassembly I sprayed the front and rear panels, and added my preferred DecaDry white lettering and a protective coat of  clear satin sealer. It’s now resplendent with all the expected features of a SSB/CW monoband portable rig.

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