Low-band AM Tx: Power supplies

Complete 500W variable regulated DC power supply assembly.

This post describes the power supplies for a 200 watt AM transmitter. There are four independent DC regulated supplies. The ‘high tension’ (HT) supply delivers 0 to 100 volts at 5 amps steady to the modulator, and is sized for a continuous 200 watt AM carrier (with 800 watts of peak power in the sidebands). Two regular 12 volt linear regulated supplies power the 12 volt circuitry (independent 12 volt supplies is a way of keeping digital and other noise off the modulator and driver stages).

Low-band AM Tx: Pulse Width Modulator and Preamp

This post describes the modulator section of a 200 watt dual-band (160 and 80m) AM transmitter, built during the COVID-19 first-wave lockdowns in Melbourne. The transmitter is fully solid state, runs cool to luke-warm at 85 to 90% efficiency, and produces high quality AM on the two lower amateur bands.

Low-band AM Tx: RF Deck

‘RF deck’ is a term that describes the RF power modules in a transmitter or linear amplifier. In this 200 watt 160 and 80m AM transmitter, the RF deck consists of two identical FET RF modules each with its own driver, an RF power combiner, the band switched Low Pass Filter module, a Transmit/Receive switching relay, and an SWR and RF power sampling module.

Low-band AM Tx: Digital VFO/Controller

Lockdown has made 2020 a year unlike any other. Melburnians were dealt a long and painful period of isolation with a CoronaVirus second wave, from around July to September, still in force, and looking like continuing to (at least partially) keep us housebound for some months yet. Days merge together, work and leisure time is largely indistinguishable. People are rediscovering reading, knitting, and endlessly bingeing TV. Makers are melting solder and stringing wires in the air.

Mt Ritchie VK3/VC-003 and Mt Toolebewong VK3/VC-033

Paul VK3HN and David VK3KR.

David VK3KR and I made plans for a visit to Mt Ritchie VK3/VC-003, 1255m (8 pts) and Mt Toolebewong VK3/VC-033, 735m (4 pts). This would be our first use of the approach from the north, rather than using the usual 8km round trip via Road 15 (from Acheron Way) then Road 10. While the southern route is a great hike in the Yarra Ranges, it takes up most of a day. But more so, some more skilled cartographers than I have determined that an alternate route in, from the north, has greater clearance from the water catchment area boundary. Two good reasons to choose the new route, from the north.

Digital SWR and Power Meter

This module is an analogue and digital SWR and power meter/monitor, designed to replace analogue SWR and power metering in an AM Transmitter project. Of equal importance was the ability to detect high SWR and raise an interlock (a control line) to inhibit transmitter power in the presence of unreasonably high SWR. I make no claim to either SWR or power accuracy; my version is an indicative tool and an interesting experiment, not an accurate test equipment, although it could be made into same with some skill and patience.

Ten Tec Model 1056 DC Receiver – is it any good, and what to do with it?

One of life’s simple pleasures is to rediscover something that bought you engagement and enjoyment in the past. And in COVID lockdown, stuck at home, it’s the perfect time to rummage through boxes in dark corners to sort, throw out, and rediscover old treasures. So it was that I came across this Ten Tec direct conversion receiver board, built around 20 years ago.

Something old, something new: A four-band 5W/50W SSB/CW transceiver (‘Summit Prowler 7’)

‘Summit Prowler 7’ is my name for this scratch-built multiband SSB and CW transceiver. This rig covers four of the most popular portable, Parks and SOTA bands — 80, 40, 30 and 20m, at a power level of 5 watts, but with an in-built switchable 50 watt power amplifier, so that you have the option to call up the extra power if the going gets rough. The rig weights in at around 1 kilogram or 2.2 pounds, about the same as an FT-817, and is similarly sized. It’s a rig for a wide range of portable situations, and is equally at home on the shack bench.

Pocket-sized homebrew 40m CW QRPp/QRP transceiver

In May 2019 I activated Mt Dandenong VK3/VC-025 with my latest homebrew rig. It was a CW only activation, five QSOs completed, but while I was handing out 599s, the reports coming back to me from the chasers were well down. Over the next few days on OZSOTA (the VK SOTA discussion group) several chasers made comments to the effect that they could hear other VK3s but nothing much from me. When regulars Tony VK3CAT, Ron VK3AFW and Gerard VK2IO reported the same thing, the evidence for a problem at my end mounted.

Social distancing project #1: Lightweight Linked Dipole

The coronavirus has stopped just about everything, and is undoubtedly changing our lives forever. With almost every group or event cancelled, there are predictions of mass boredom and social isolation. Many people apparently have no idea what they’ll find to do with their time. How odd. That’s never been a problem for makers like me. So in the interests of the bored and isolated, I offer this story of something useful that can be made in an afternoon — a linked dipole.