Those TV sets didn't just make audio at that frequency, they blasted it out on the radio waves as well with harmonics going all through the LF and VLF bands. It's much quieter there now with most of the CRT sets gone.,(reply>), If you can't hear the morse code at the end card, put a portable AM radio tuned to around 530 KHz up to your computer's speakers. You can clearly hear it thru the AM radio. Turn up your computer's volume to max.