Category Archives: maker

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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VK3YE’s ‘non-invasive’ LED-LDR AGC add-on

When I saw the AGC circuit by Peter Parker VK3YE, I realised it solved a problem common to many simple homebrew receivers.  You cannot automatically control the gain of a receiver with fixed gain stages. Most simple receivers do not have IF stages, let alone variable gain IFs. And the LM386 has no gain control. So it’s easy enough to sample the audio at the volume potentiometer, amplify it, rectify it for a source of AGC. But then you need a voltage controlled gain stage ( a Voltage Controlled Amplifier  or VCA).  If your receiver doesn’t have one, AGC won’t work, and you with have to either add a VCA in the receiver somewhere or replace one of the fixed gain stages with a VCA.  Until now.

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Arduino CW keyer for a BiTx or other homebrew rig

It’s been 3 years since I got my MST400 Mk 1 40 meter SSB transceiver going and started using it for SOTA activations. For those not familiar with it, it’s like a kit version of the BiTx40 from 2013. It has a similarly spec’d monoband superhet receiver, 10MHz IF, and IRF510 5 watt power stage. The circuit on a page is here. It’s been with me for nearly all of my 65 activations (over 400 SOTA activation points) around VK3. Now, with HF propagation approaching cycle lows, it is time to do what I should have done ages ago… add CW.

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Homebrew 160 meter AM/CW transmitter receiver

The VK 160 and AM SOTA event (1st April 2017) provided the deadline pressure needed to complete this build. The rig is a separate transmitter and receiver, so seeing as there are no shared modules, I shall call it a trans-receiver rather than transceiver. The designs for both transmitter and receiver are by Drew Diamond VK3XU. See Drew’s Projects Volume 3  book for full details, available from the WIA or RSGB. I posted details of the 160m AM receiver when I first built it, a year ago. At that time I also built the transmitter and power supply. I got the transmitter going but blew up the PA FET (BUZ90). During the long wait for replacements, I shelved the build and moved onto something else. Now, thanks to SOTA, it is finished.


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On repair

My mower broke last time I used it. Payback for all the times I have mistreated it, yanked its handle, tilted it on 2 wheels over a gutter, or banged it roughly into a tree stump. The chassis rusted out where the handle attaches, so much so that the handle on the left side pulled off, taking with it a nicely rectangular chunk of rusted mower.  So I did what any self respecting man would do. I left it in the shed and ignored it.

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