LW on the PL-380
Experiments to make the PL-380 play better on LW are encouraging. The MW coil with Hoop Loop coupling winding were replaced with a 3300-uH coil wound on an FT114-61 toroid. While -61 is not the best mixture for LW and the 1.14-inch-diameter toroid was small for the number of turns required (about 180), it's what I had. With this coil, the PL-380 will tune from 150 to about 510 kHz. The Hoop Loop is coupled through a 15-turn primary. The new coil hangs out the top of the radio, as it's too large to fit inside.
I verified the Hoop Loop was tuning with the radio by holding a G8 tuned to a beacon station it couldn't hear, in the middle of the loop. Then I turned on the PL-380 and tuned it to the same frequency. Even though the G8's antenna won't tune to LW, the station became audible. Tuning the PL-380 up or down from that frequency made the signal on the G8 go away, verifying that the loop was tuning properly. If you have a second receiver that covers the same frequency range, you can do this test with any external antenna tuned by the radio. Even though the new coil won't tune to 530 kHz, R. Enciclopedia was still good copy, as was the ZLS Stella Maris beacon (526 kHz) in the Bahamas. That beacon is a beast; I often hear it on my car radio tuned to 530 kHz.
The mods were complete three hours before sunset yesterday, and right away they paid off. Previously, the only LW station I could hear was a beacon about 20 miles away, on 405 kHz. It sends the number 5 in Morse Code. With the new coil in place and the Hoop Loop plugged in, I logged three new beacons right away. They ranged from SQT in Melbourne, FL, about 80 miles north, to FIS in Key West, about 150 miles south.
After sunset things got even better, as the log below shows. I had good copy on the German-183 kHz, and weak audio on France-216 and Algeria-198, but they weren't good enough to log. Best NDB DX was DDP, San Juan, PR, about 1000 miles. What's interesting and a little ironic is, although I logged two Cayman Islands beacons, I couldn't copy any Cubans! The Caymans are on the other side of Cuba, so this is a mystery. The last time I DXed LW was from the Bahamas, 15 years ago. My best results were at sunrise, but this morning brought no new loggings.
The LC ratio of this modification is pretty high. I've worked out a way to pad the internal tuning varactor with a fixed cap; this means breaking LW into two segments, 150-290 and 250-510 kHz, using two coils (2250 and 750 uH). The Hoop Loop is small for LW, but under the right conditions I think I'll be able to hear European BC stations (which I would much prefer to beacons!). Building the two LW coils and the MW coil into small plastic boxes and installing a connector on the top of the radio, will make it easier to change bands. It will also let me use a larger toroid for the MW coil, which should help a little.
Here's the first night's log: