A couple of DIY shortwave radio receivers and a new antenna
Posted: Sun Aug 25, 2024 7:36 am
Anywhoos. That hobby has been mostly dorment for a number of years, but I got struck by a spark of interest for it lately. So I dug out a pair of my homemade portable (arguably) receivers, only to realize both needed new batteries. They both were built with 12V lead acid batteries for cheapness and ease of use. These are of course all dead after about a decade. The focus got shifted to the left one in the image, since it's easier to modify and upgrade. I built a lithium battery pack for it with a proper BMS and a buck-boost converter to take a varying voltage in for charging, and output a steady 12.6V for the battery pack. This is not a looker by any means, so I wont even take it apart to show it. It's really nothing exciting anyways.
But as these are small portable devices, I've always dabbled with building active, so called 'miniwhip' antennas, that compared to traditional antennas are capacitive rather than magnetic. This means they can be small. I mean, *really* small. Let's say they want to listen to the 80m band (about 3.5MHz) you would ideally want a half-wave antenna, and for portability that would be a longwire. But that would mean you have a 40 meter long wire to hang up, ideally far up and in a straight line. Instead you can have this little active circuit board, where the large copper pad to the left is the actual antenna element. These only work for reception however. But it's ideal in my case. As it is an active antenna it also needs a bit of circuitry on the radio end to feed power into the coax to power the antenna through the same cable.
I've hand made several of these antennas in the past with very varying results, so the plan is to finally get around to building one properly, and also modify it a bit to suit my needs.