Fax pass-through poor quality

Dear Sirs,

I have poor quality on fax pass-through in my setup: PSTN->Asterisk->Alcatel->FaxMachine, voice calls are fine. Researching in another posts, seems this could be a time sync issue between cards

Due i have 2 Te210 Cards, i will try to link channels only inside same card to avoid time sync issues, i mean Calls from Span 0 always be linked to the span 1 in the same card, and calls from span 2 will be linked to span 3.

Do you thing this could help to fix the fax quality?

if so, could you suggest me some way to know from the dialplan the span or group of the current active zap channel?

Thanks in Advance.

Just for the record,

Linking zap channels only inside same card fix the issue, another way is conecting cards with a time sync cable from digium.

Regarding the way to do is a basic thing: zaptel context in zapata.conf.