Category Archives: Portable

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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Three summits on Mt Buffalo: The Hump (VK3/VE-019), The Horn (VE-014) and Mt McLeod (VE-034) 2017

The annual Australia Day holiday, Thursday January 26th 2017, set up an opportunity for a break and some alpine walking and activating.  Leaving Melbourne on Wednesday 25th I drove to Mt Buffalo and camped at Lake Catani on the Mt Buffalo plateau. Mt Buffalo is a mountain plateau (1400 meters) and national park, about 350 km north east of Melbourne.  This is a sub-alpine camp site which must be reserved ahead of arrival with Parks Victoria. There are lots of good camping spots under low snow-gums, a pristine fresh water lake that you can swim in, hot showers, no drinking water, and (apparently) a population of endemic dingoes.  Just down the road is former ski spot Dingo Dell, where I’ve ski’d many years earlier.  I had no idea that it is named after these Australian native dogs.

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Mt Feathertop (VK3/VE-002) 2017

Mt Feathertop (VK3/VE-002), 1922m, 10 Points, is the second highest mountain in Victoria.  Along with Mt Bogong and other summits and highlights along the Australian Alps Walking Track it is a popular hiking destination for more experienced and fit bushwalkers.  A number of sites offer advice and information for climbers.  So far there have been 6 SOTA activations (since first activated by Wayne VK3WAM in 2013).

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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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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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