This

my %packet_fields = (
   $Idents{ Format_7 }    => qw(    ident
            flags
            x
...
[download]

Should be:

my %packet_fields = (
   $Idents{ Format_7 }    => [qw(    ident
            flags
            x
...]
[download]

Likewise, this:

   $Idents{ Format_7 } => qw(ident
                RDP_Ident
                Radar_Site_Ident
                site_x
[download]

Should be this:

 $Idents{ Format_7 } => [qw(ident
                RDP_Ident
                Radar_Site_Ident
                site_x
... ]
[download]

The value of a key must be a scalar or *reference* to an array or hash, not an actual array or hash, as you had in your code. Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality