Northern with 40mer oligo

[Patrice Marion]

Excuse my english, I'm french speaking.
Is anyone have a GOOD protocole for Northern hybridization with a 40mer 
oligo ? I have look at several formulas to figure out the Tm and all of 
them give different results. I am working with hybridization solution 
containing 5 X SSPE, no formamide, my oligos are 52% to 54% GC (100% 
homology). The Tm-25 I obtained (for hybridization) is around 37 C.  Does 
it look right ? 
What kind of wash solution sould I use ? Can I go high stringency with 
oligos (i.e. 0,2 SSC) without loosing the signal?

Thanks in advance,
Pat