First – get the oid of the snr – it consists of
.1.3.6.1.4.1.41112.1.4.7.1.3.1 followed by the mac address of the radio intoerface. to get it

snmpwalk -v 1 -c CommunityString IP.Add.r.ess .1.3.6.1.4.1.41112.1.4.7.1.3.1

you should get a value like:
.1.3.6.1.4.1.41112.1.4.7.1.3.1.36.90.76.236.135.45 = INTEGER: -59

now set up a graph for the above oid