Tag Archives: homebrew

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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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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More power to the activator (choosing a new LiFePO4 pack)

When the time came recently for a new battery, I jumped onto HobbyKing and was bewildered by the range of options, even after limiting the search to a particular current capacity, in my case 4-5AH, and 4S (4 cells). Wishing to leverage the ‘wisdom of the SOTA crowd’, and at risk of reopening the “whats the best battery for SOTA” chestnut, I posted to the yahoo SOTA_Australia group:

I’m buying another LiPo from HobbyKing. This battery will be for general purpose 5 watt txcvr use, but will also be used to power an afterburner of the W6JL type, using a pair of IRF2Z24N hexFETs, for up to 50 watts. My question is, what do I make of the discharge figure on the LiPo packs, which varies from 10c to 35c? I presume this is the rate at which the battery can supply current under load, the higher the better. A higher discharge figure might be important when powering an afterburner, which might draw current peaks of many amps on voice peaks. Prices seem to correspond with higher discharge figures, from as low as $25 (10c) up to $55 (35c) for packs around the 4AH rating.

My only current Li-XXX asset.  

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2016/17 rollover party on Mt Disappointment VK3/Vc-014, and the christening of ‘Summit Prowler Two’

I left my plans for 2016/17 rollover late, and when I checked sotawatch alerts 24 hours out, there must have been 15 summits manned. From lunchtime on I was due at my brother’s QTH in Doreen, north of Melbourne. So I chose Mt Disappointment, which is an hour’s drive from my place and 45 minutes drive from the lunch destination. This gave me time for a leisurely activation on the picnic table near the summit. This was also to be my first attempt to activate a summit on 30 meters CW with the newly finished Wilderness SST rig.  It all went to plan. With 4 CW QSOs on 30 meters bagged, I switched to 40 after rollover for a bunch of hunt-and-pounce QSOs. Here’s a video that offers a taste of the CW and SSB signals heard and worked.

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