There’s a reason why most homebrew transceiver kits and scratch-built projects are monoband and single mode — theres a chance you’ll finish it, or at least, get it working for a while. Building a multiband HF transceiver is a big job, as any homebrewer who has attempted it will tell you. It may take years.
Weak Signal Propagation Reporter is a global radio propagation monitoring and reporting network comprised of thousands of low power beacons operating on the amateur radio bands. WSPR beacons can be detected from the lowest of Medium Wave frequencies (137kHz) all the way through the HF spectrum (all the bands from 160m to 10m are popular) to the VHF bands, 50 and 144MHz. WSPR receivers decode the tiny beacon packets and upload them to a central database, at WSPRNet.org, where anyone can literally ‘see’ the propagation paths that are currently open.
The bottom ends of 80, 40 and 20m are not what they used to be. For starters, the busiest part is the digital segment where computers talk to computers – listening to this segment is like eavesdropping on a bunch of dialup bulletin boards having a party in 1983. Then there’s the CW segment. When there are CW signals to listen to, all are frequency stable, chirp and click-free, generated by more computers from deep inside rigs that are more computer than radio. These shining examples of digital CW perfection have traded efficiency and quality… for personality.
This AM solid state Class D single band transmitter was assembled over a three year period. Started in 2018, it’s first configuration used a 100 watt push pull RF module published by Drew Diamond VK3XU in Amateur Radio magazine, modulated by a 200 watt linear power amplifier driving a reversed mains transformer, available as a kit from local supplier Jaycar. I built up the RF board, 50 volt power supply (using a stock 300VA toroids mains transformer, no regulator) and proceeded to destroy half a dozen power FETs (STW20NM50) in the RF power stage. Realising I didn’t really know what I was doing, I wisely put it aside.
I’ve long been interested in compact and fairly minimal SSB and CW rigs with good performance. I’m not into bells, whistles or menus. Menus are for restaurants! When hiking, walking or bouncing around summits I want to minimise things that are not absolutely necessary, things that can go wrong. Less is more when it comes to a transceiver for portable work.
Ten meters or the 28MHz band is showing glimmers of life from sunspot cycle 25. Even so, its not an obvious choice if you want to build a portable SSB monobander and have lots of contacts. But 28MHz is the IF of choice for VHF and UHF transverters. After noticing the 6, 2 and 70cm transverters available on eBay from the workshop of UR3LMZ and the good reports from buyers, I cooked up the idea to build a 28MHz ‘transverter IF’ transceiver, to be paired with one or more VHF or UHF transverters.
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).
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.
‘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.
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.