Without knowing details of your card and source, it's not really possible to say if you can record below 20HZ - best idea is to try it and see! I expect it will probably work.
As far as I know, Audacity is limited only by the space available on your hard drive. However, some users have found problems letting the program go until the disc is actually full and runs out of space, so better to avoid it if you can.

Kind Regards
----- Original Message -----
From: jacot
To: audacity-users@lists.sourceforge.net
Sent: 30 March 2011 13:37
Subject: [Audacity-users] record below 20 hz and for 4H long posssible or not

1- I have to record below 20hz  signal 
is it possible whit audacity and audio card 
how can be modified my audio card for
2- the record have to be for 4H  or more what the limit of audacity
jack 47'n 71'w

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