A 300w switching regulator for a QRO AM transmitter power supply

Laurie VK3SJ is an accomplished RF designer and homebrewer in Melbourne’s 160m scene. You can hear his excellent AM signal regularly on the 160m AM Coffee Break net most weekdays. Laurie has spent a great deal of time experimenting with Class D, E and Pulse Width Modulators. He has an interesting Class D AM transmitter design with a pulse width modulator. Laurie’s design has been built by Wayne VK3ALK, who I met online in the Class E Forum on AMFone. After lots of emails and a few calls with these homebrew AM experts, I decided to proceed with my build of a VK3SJ AM transmitter for 160m.

Continue reading
Tagged , , , ,

A Pulse Width Modulator for the FAT5 160M Class E Transmitter

After a few months of operating my FAT5 160m AM Class E transmitter with its linear modulator, it was time to try Dave and Eric’s Pulse Width Modular module (PuWMa). This is a PWM using the Texas Instruments’ UCC25701 PWM chip, with TC4421 drivers and IRF640 switching FETs, followed by the obligatory Low Pass Filter to clean the 170kHz AC off the modulated DC.

Continue reading
Tagged , , , ,

Microphone Compressor from 1978 lives again (ETI490)

Whilst sorting electronics junk recently I unearthed this board. My build of the Electronics Today International microphone compressor, ETI490, published in the magazine in December 1978. I remember preserving my copy of this magazine for many years, long after the pages faded and cover tattered, as it contained the construction article for this useful amateur radio station component.

Continue reading
Tagged , ,

Summit Prowler 6: A pocket-sized SSB/CW transceiver for 80, 40, 30 and 20m

Peter DK7IH is a master of compact homebrew transceivers. I’ve been reading his excellent blog where he chronicles more than half a dozen homebrew HF transceivers and related projects. Most are compact SSB superhet transceivers with digital VFOs, AGC, metering and PAs in the range 5 to 50 watts. A few of these rigs are just so remarkably tiny I wonder how he has the persistence and patience, not to mention how he gets them stable. With Peter’s fine examples in my head, I started daydreaming about a compact SSB/CW transceiver, hoping to go a fair bit smaller than my slightly chunky attempt at a hand-held from last year.

Continue reading

Tagged , ,

160m 100W Class-E AM transmitter (FAT5)

The FAT5 project is a 100 watt Class E AM transmitter from Dave GW4GTE and Eric GW8LJJ, dating back to 2011. The name derives from Dave’s desire to design a 100 watt AM workhorse using contemporary FETs to rival the ubiquitous AT5, a widely used war surplus boat anchor for low band AM.

Continue reading

Tagged , , , ,

Mt Hotham SOTA Weekend Feb 2-3 2019

A brief post to share a short video from last week’s Mt Hotham SOTA weekend. Once again, Brian VK3BCM hosted several dozen SOTA and mountaineering enthusiasts at Anton Huette Lodge, Mt Hotham, for two days of summit bagging and SOTA talk. On the way up I activated the two ‘easy’ summits on the Mt Buffalo plateau, The Hump and The Horn.

Continue reading

Tagged

Homebrew 50 watt amplifier for 80-17m (W6JL)

Don W6JL’s 50 watt FET amplifier is a popular afterburner for FT817s and other QRP rigs and exciters. Don won the QST Homebrew contest in 2009 with this design. The amp offers a useful order of magnitude (12dB) power lift over QRP levels, and apart from the power FETs can be built from an averagely stocked junk box. The FETs are commonplace and cheap — they can be bought for as little as 98c each!

Continue reading

Tagged , , ,

Mt Bogong (VK3/VE-001), 21st Jan 2019

Mt Bogong (1986m ASL) is Victoria’s highest mountain. All the tracks to the summit involve a steep climb, none more so than the Staircase Trail, a 1200m ascent over just 6.5km linear distance. Although I’d just completed a 2 day walk in to Mt Feathertop (Victoria’s second highest peak) the previous two days, various factors combined to nudge me to arrive at the Staircase Trail around 0830 on Monday 21 Jan 2019, a little bit apprehensive about the energy level that would be required to get to the top that day, and the temperature I’d be walking in — hot. The previous days had been high 30s (Celsius), and the hot summer week would peak at 42C in the valley the day after.

Continue reading

Mt Feathertop (VK3/VE-002), 19th Jan 2019

This year I tackled Feathertop as an overnight walk, leaving the car on the side of the Alpine Highway near Diamantina Hut at 1645 on Saturday 19th Jan 2019, after having driven up from Melbourne. It was about an hour later than I’d hoped for, but a daylight savings sunset time of 2032 gave me nearly 4 hours in the warm but cooling air to get to Federation Hut. The walk in along the Razorback Trail was in good conditions, but I was carrying my SOTA kit and camping gear, not well optimised, way too much weight, and it all started to hurt in the last hour. I met at least a dozen summiteers on their return leg, some looking like troops limping back from a battle, a few considerably worse for wear. More on this later.

Continue reading

Tagged , , , , , ,
Shack of VK2KMI

Ham Radio Blog of VK2KMI

Ham Historian

A passionate amateur looks at Melbourne history

R.IT

My journey of repairing and recycling anything I put my hands on that I believe is still useful. Not just hardware, but including software with relevant content and issues in the field of Cyber Security, Vulnerability Scanning and Penetration Testing.

G4YDM Ham-Radio and SWL news

Radio craft, homebrew, QRP/SOTA, AM

VK1DA.blog

Amateur radio experiences with VK1DA

Tj Lab

信号処理とラジオ

The Microscopic New Yankee Make Shop

Bits of technology and illogic by WA2MZE

Paul Gacek

W6PNG/M0SNA

NewURL: https://dk7ih.de

This blog is no longer in use!