Category Archives: AM

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.

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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.

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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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Listening to West Coast AM on 75 meters

Standing on  a crowded commuter train, going home at the end of the work day in Melbourne Australia, listening to a late night west coast AM QSO on 75 meters, 3870khz, using my Samsung smart phone, via W7RNA’s web SDR.  This is just one of the miracles of SDR and the Internet — the ability to use someone else’s station anywhere in the world, from almost anywhere in the world. My old elmer from my school days in the 1970s, Moss VK5TU, would turn his tuning knob in his grave if he could see this. KB6 and WB6es chewing the rag, on big AM transmitters.  You can almost smell the burning dust on the ultraviolet glass envelopes.  Pressing the tiny audio buds into my ear to shield some of the ambient train noise I hear the tone of the transmitter, rounded low-mids and bass.  It could be 1972. It’s a nostalgic and beautiful sound.

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