Paul Nicholson wrote an excellent article explaining the fundamental principle behind forward error correction codes.
It does not discuss any particular coding scheme (Convolutional, Reed-Solomon, LDPC, and so on), rather, the intent is to home in on the underlying principle that all forward error correction schemes exploit. This is done so without using any mathematics at all, well perhaps just a little simple arithmetic.
On September15th Roger, VK4YB, and Steve, VE7SL, successfully completed a two-way JT9 QSO after a few previous attempts. With a distance of 11802 km, this QSO is believed to be the longest two-way QSO ever completed under amateur service rules on 630 meter.