Category Archives: SOTA

A scratchbuilt G6LBQ BiTx ‘Walkie-Talkie’ for 40 and 20m SSB/CW

After completing a 6-band SSB/CW QRP transceiver (Summit Prowler IV) I found myself thinking about a more compact QRP SSB/CW rig for SOTA, with two of the main day-time SOTA HF bands (40/20m). The design driver this time was to try a different ‘form factor’ — I wanted a rig with a narrow and long case, such that it would easily slide inside a backpack, and on a summit sit vertically against a rock or be hand held. All my SOTA rigs so far use both front and back panels for connections and controls, so they need to sit level on a horizontal surface. As most rocks or tree stumps are low, you can’t easily read the display. Some designers get around this by putting the display on the top of the box, a sensible adaptation but one that makes the rig look like a flounder. Because I spend a lot of time building and using these radios at home on the shack bench as well as on a summit, I wanted a design for use in both situations.

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Federation Range (VK3/VN-029) ski day, 2018

Last year I cross country ski’d into Federation Range VK3/VN-029, 1490 meters above sea level, activated it for 8 points (+3 winter bonus points) and ski’d out again. This is possible because this summit is just off groomed cross country ski tracks at Lake Mountain, ninety minutes north east of Melbourne, a popular sight-seeing, tobogganing and cross country skiing spot. Time to do it again. After picking up skis at Marysville I took Royston Trail from the car park up the long incline, to Panorama, then Hut Trail to Boundary Hut, the remains of a hiking hut, long since burned out, only the stone walls standing to waist height. Distance out is about 4km.

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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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‘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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Mt Hotham SOTA Weekend Feb 2-4 2018

VK3’s ARH, YY and PF on Mt Murray.

On the weekend of the 3rd and 4th Feb 2018 I joined about 18 others at Brian VK3MCD’s now annual VK Mt Hotham SOTA weekend, starting with a night on Mt Buffalo camping at Lake Catani the night before, and with some activations at Falls Creek on Friday. With the summits at Mt Buffalo (The Horn, The Hump) and Falls Creek (Mt Nelse, Mt Cope), then 2 days four wheel driving, I accumulated 124 activator points.  A productive long weekend!

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Mt Torbreck, Pyramid Hill and Sugarloaf Peak 2017

The Melbourne Cup, a hugely hyped horse race affords Melburnians with a three day long weekend, allowing yours truly, being disinterested in all things equestrian, a day in the Victorian mountains, my first activations for more than 3 months. Mt Torbreck VK3/VN-001 in the Rubicon Range just south of Eildon would start the day, followed by nearby Pyramid Hill and the peak in the Cathedral Ranges if time and energy allowed.  Leaving Melbourne suburbs early, I turned the ignition key at 6:10am and drove towards Eildon, then south down Snobs Creek Rd to Conns Gap Rd, parking at Barnewall Plains Track by 0812, 2 hours and 2 minutes drive time.  The temperature was 8.5C.  The gate was open and a proper 4WD would have ploughed up the first steep section, but I happily walked the kilometer or so to the camping area then up the track to the summit. Steep, but with rewarding scenery, although the summit was in mist and just under cloud.

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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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Three Summits in the Yarra Ranges: Federation Range, Mt Strickland and Mt Donna Buang

Activators have been bemoaning the poor state of HF propagation recently. But when planning an August SOTA activation in Melbourne, the propagation forecast runs a distant second to the weather forecast. If the HF propagation is bad you might not get the 4 contacts, but if the weather is bad you might get seriously bogged or snowed in.  If nothing else you’ll come home wet and miserable.  So I studied the weather report carefully for Friday the 4th of August. A series of three low pressure systems of varying strength were on the weather map bringing low temperatures, strong winds, rain and snow down to 900 meters. Friday morning looked to afford a break. I considered Mt Matlock (VK3/VC-001) but when the morning came after an evening of steady rain I opted for Federation Range (VK3/VN-029) near Lake Mountain, figuring that walking 5km each way through slushy snow would be better than driving 50km each way along the pot-holed water-logged C511. As it happened, it was the right choice.

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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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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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