Apex domains cannot have CNAME records.
Question and response
Question
dig pdxnet.uk. NS
Answer
pdxnet.uk. 5 NS nebula.ns.pdxdns.com.
pdxnet.uk. 5 NS apollo.ns.pdxdns.net.
pdxnet.uk. 5 NS nova.ns.pdxdns.co.uk.
pdxnet.uk. 5 NS orbit.ns.pdxdns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0