I recently cut this small piece Veroboard to hold two vertically aligned miniature potentiometers on a receiver front panel. The three soldered tracks to the right allow connection of the audio signal to the volume control using shielded twin conductor cable. Very standard stuff, I’ve been wiring up audio amplifiers to volume controls like this for about four decades. But this one wouldn’t work. It has a fault — it’s there, in the picture above, right in front of your eyes… can you see it?
‘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‘.
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!
Charlie ZL2CTM has been pushing out a series of excellent videos on his YouTube channel that take you through the circuit design, making and testing of superhet SSB transceiver modules. Yesterday my eyebrow involuntarily raised ever so slightly at his use of Veroboard as the substrate for his latest 8MHz crystal filter. Veroboard? At radio frequencies? Veroboard et les fréquences radio ne sont pas compatibles!
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.
I’ve included 630 meters in my 8 band Progressive Receiver project. Not that I expect to hear much LF CW, but down the track I hope to hook up a shack computer for FT-8, WSPR or whatever weak signal digi mode they use down there. 630m is a playground for homebrew transmitters and receivers. For example, Dimitris VK1SV has some simple but impressive class E transmitters using the familiar IRF5xx switching FETs. You can get a lot of bang for your buck out of any transistor or FET operating at 470kHz. So including 630m in my receiver creates opportunities for future play!
Using metal can transistor radio IFTs as the tuned elements of a BPF is just such an obvious and neat idea. A pack of four IFTs is available from Jaycar, three cans for the 455kHz IF and one (red) for the oscillator. VK1SV built a 630m filter with two, whereas Steph VK5ZSV went as far as five. My filter uses four, mainly because the white ones come 2 in a pack, so my investment was 2 packs (about $10). The video shows a band scan with the filter out, then in. Thanks to VK1SV and VK5ZVS for publishing their designs on their sites.
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.
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.
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.
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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