Here's part of a post I made to our wpaNBEMS yahoo group which has tips for newer users of MT63. Try NBEMS/FLDIGI with the WRAP checksum feature.
We had a great ragchew net tonight with yet another new check in who copied our MT63 bulletin on his first try. Actually, we almost had a clean sweep on the MT63 bulletin tonight, and I'd like to shoot for 100% all around the table.
MT63 can be a bit tricky. Make sure you go to configure, modems, and then to the MT63 tab to make sure you have 64 bit interleave and extended characters checked.
I think one of the key issues with MT63 is calibration of the sound card. We've discussed this before but we have a lot of new folks here so I'd like to point to the calibration instruction on our website:
Also, I did a uTIPu video on calibration that folks might find helpful:
One thing to keep in mind with MT63 is the tuning on the waterfall is somewhat critical, but I think this is more of an issue due to the relatively light signature as compared to Olivia and some of the narrower modes. You can just see Olivia better on the waterfall and you'll notice that Olivia produces 2 sets of alternating tones at the beginning of each transmission, which really show up well and helps receiving stations tune to the signal. MT63 1k long (64 bit interleave) is really spread out over the audio spectrum and much harder to see especially under weak conditions.
To help with tuning on MT63, we put out a 1k tone (see the tune button at the top right side of the FLDIGI screen) before we transmit the MT63 signal so that receiving stations can center the tone to the 1000 Hz mark on the waterfall using the rig VFO in fine tune mode.
Here's another very important point regarding the tuning of MT63... once the transmission starts, receiving stations will take up to 15 seconds or so for the software to grind away at the massive amount of forward error correction. This is normal. But a big mistake I made when first trying to copy MT63 on HF was to not wait for decode, and I would try to re-tune while trying to receive the signal. Each time you re-tune, you have another 15 seconds or so before the software syncs and if you constantly re-tune, it'll never produce any print.