Category Archives: SOTA

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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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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160m SOTA VK Challenge, 1st April 2017 (Mt Gordon VN-027)

The VK SOTA 160m and AM Day event provided the motivation I needed to finish off my VK3XU 160m trans-receiver. It is a separate crystal controlled  transmitter and receiver in the same box. The transmitter is a 30 watt class E transmitter with crystal oscillator, CMOS logic gate driver and BUZ90 FET PA. The receiver is a superhet with SA612 mixer and VFO, 455khz IF, MK484 AM detector, and TDA7052A audio stage. Further details in an earlier post. The modulator is an LM3876 that drives a backwards power transformer as the modulation transformer. Both transmitter and receiver have previously been tested, however, I blew the FET and had to wait what seemed like several months for an eBay replacement. In the mean time the project got shelved, until last week.

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Hotham SOTA weekend 2017

Q: How many SOTA activators does it take to change a light globe?

A: Nine. One to alert the impending globe change (subject to weather), one to take the bulb and socket to the top of a summit, one to spot when in sight of the bulb, four to replace the bulb while logging UTC and local conditions, one to take photos as the replacement is done, and one to upload the globe replacement details into an online database and write about it all on a blog.

Nine. That’s how many VK3s spent the weekend at Peninsula ski lodge on Mt Hotham for the 2017 SOTA Hotham weekend. It was my first attendance. I met Brian VK3MCD, Peter 3PF, Alan 3FDIM, Ken 3KIM, Ron 3AFW, Glen 3YY, Allen 3ARH, Tony 3CAT and Ron and Glen’s partners for two days of SOTA activations, map reading and socialising.

 Morning of Sunday 26th Feb 2017, looking out the Peninsula lodge window south.  

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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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