In this day and age, with cheap online shopping, software defined radio and bargain-basement Baofengs from China, the upstart radio ham is spoilt for choice. Of course, there’s nothing quite like the charm of keying up your own homebrewed rig, cooked up in the garage from scratch. [Paul], aka [VK3HN], knows just how it feels, and put together an epic 200 watt Class D AM rig to blast his signal on the airwaves.
The amount of effort that has gone into the build is huge. There are handwound coils for the PWM low-pass filter, and the PCB is home-etched in ferric chloride, doing things the old-school way. There’s also a healthy pile of dead components that sacrificed their lives in the development of this build. Perhaps our favorite part is the general aesthetic – we can’t get over the combination of hand-drawn copper traces and off-the-shelf Arduinos.
It’s a build that far exceeds the Australian legal limits, so it only gets keyed up to 120W in real use. This has the benefit of keeping the radio operating far in the safety zone for its components, helping keep things cool and stable. We’re sure [Paul] will be getting some great contacts on this rig. If you’re suffering from low power yourself, consider an amplifer build. Video after the break.
[Thanks to Ben for the tip!]
Nice build Paul, look forward to more in the future!
73’s
Scoldog, a VK2
Theres still someone using AM on the HAM radio bands? nice build anyway, would make a great radio transmitter for local stations. 73s from OE3 :)
https://www.w8ji.com/transmitter_splatter.htm
“Strongly discouraging use of enhanced bass and treble on crowded bands. It has no place on crowded band or near weak signals. Wide-Fi is selfish and inconsiderate even when it uses a 3kHz filter because of the increase in level and frequency spread of IM products. ”
Couldn’t have said it better myself. HF spectrum is limited. If you want to eat up spectrum with unnecessary fidelity, go up to the microwave bands.
Perhaps “on crowded bands or near weak signals”, but on the 160 metre band here in VK land, which is dead at all times outside of 1100 AEST, hi-fi excursions are quite acceptable and pleasing to the ear.
This transmitter is not using enhanced audio bandwidth, it is relatively flat, no equalisation.
It is not uncommon for people to procure old low power commercial broadcast band transmitters and re-tune them to the 160 meter ham band. A project I would enjoy undertaking someday. They sound really good, and are rated for continuous operation.
Much less common today than 30 years ago. From listening to some of the ‘monologues’ I’ve heard on 75 meters I always imagine a giant, 2 foot knife switch on the far wall of the shack. The OM heaves the switch to the TX position, trudges around the 7 foot steel Gates cabinet and back into his chair to begin his discourse. While his comb over wafts gently in the breeze from the cooling blowers.