Tom was not referring to the sheathing on a cable but to the velocity factor of coax. Not the same thing at all.
It is well established that covering a cable with a dielectric will change its electrical length. The late LB Cebik's site (which is still accessible) quantifies exactly how much with different dielectrics. It can range up to about 7 %, and in my experience LB's figures are spot on. 73 Roger VE3ZI _______________________________________________ Stew Perry Topband Distance Challenge coming on December 29th.
