How to strongly fix N-type connector to thick RG cable?
I use paste solder, a SMD rework hot air gun with a small nozzle and a soldering iron to solder center pins in coax connectors (for connectors that do not allow crimping).
Fill the pin with paste, apply extra to the wire near the pin, heat up the pin and conductor, then hit the conductor (not the pin) with a hot iron and some additional solder to complete the joint. This helps to produce a good joint without getting solder on the outside of the pin, which usually prevents assembly of the connector