Co ax plugs are one of the best little inventions ever but they do have a nasty kick up their sleeve.
An aerial cable carries a voltage produce by the aerial itself,this is a minute voltage that carries no danger,but a voltage nonetheless less.
Like any voltage if you short it out then you are suddenly the owner of problems.The easiest to imagine is the mains when this is shorted out,can and do get a nice large bang.
Short the voltage voltage coming from an aerial then yo simply have no signal.A co ax plug must be very carefully fitted to avoid the outer braid shorting to the inner conductor,all it takes is one strand of braid and bingo no picture.
If you have made up your own co ax leads and are having problems, then carefully take the plug apart apart and check for any shorts.
A classic case of shorts in co ax plugs is if the cable as been yanked pulling the cable through the plug not all the way but sufficient to cause the short and no picture.