Coax is short for coaxial cable. It's a two-conductor cable with both the conductors on the same axis. It has a center conductor, a dielectric or insulating layer, a braided metal layer, and an outer insulating layer.
Coax is used for conducting radio-frequency signals from one point to another. The signals travel not through the metal conductors, but in the space between them.
Hooking up coax is not the same as wiring an extension cord. Coax requires special connectors. There are several kinds in use, but the PL-259, also known as the VHF connector, is most common.
There are some tricks to installing PL-259 connectors to a length of coax, but they are not hard to learn.
The PL-259 connectors are designed to look like a smooth connection to the signal travelling through the cable.
There are several thicknesses of cable. Fat cable is RG-8/U or RG-213/U. Skinny cable is RG-8-X of RG-59.
First we'll start with fat cable. It's the simplest, but not the easiest.
Notice the PL-259 connector is in two pieces. Unscrew the threaded sleeve and slip it over the wire, with the threaded end of the sleeve facing the end of the coax. Push it back out of the way. Now hold up the other part of the plug, the part with the four holes in the side and the little tube that sticks out the end. Hold it next to the end of the coax and very gently take a sharp knife and peel off enough of the outer insulating layer to more than exual the length of the plug.
Notice how far it is from the back end of the plug to the plastic insulator inside the plug. Now take a soldering gun of 100 watts or more and melt some solder onto the copper braided layer of the cable. Coat or tin the copper beginning where it comes out of the insulation for a length just a sixteenth of an inch shorter than the space between the plug's plastic insulation and the back of the plug. This will take some concentration and some effort. When this is done, unravel the loose end of the braid and trim the strands off with wire cutters. Make the end of the braid as even as possible around the diameter of the inner insulation.
Now take that sharp knife and gently cut through the inner insulation about a sixteenth of an inch away from the end of the tinned copper braid. Go all the way to the center wire, and cut all the way around. Then get a good grip and pull the insulation off. May have to slip the wire cutters into the fresh cut to get leverage, but don't damage the inside conductor.
Now take the soldering gun and very carefully melt a little bit of solder into the strands of the twisted inner conductor. Put in just enough to hold the strands together.
Now if the job is done right the connector should slide over the end of the cable, with the center conductor sticking out the little end. The solder on the braided copper conductor should be visible through the four holes in the side of the connector cylinder. Make sure the cable is in all the way. Then heat the tip end and the center conductor until solder will melt between them and fill the void. This makes a good connection.
Now comes the hard part. Melt some solder into the four holes in the connector, soldering the connector to the braid. If the connector is chrome plated, it's a good idea to file the chrome off around the holes, so you can solder directly to the brass underneath. Chrome plate does not solder well. Silver-plated surfaces solder well and do not need to be filed. Silver-plated connectors are available from electronics supply stores, but Radio Shack has only chrome-plated connectors.
After the connector assembly has cooled down, use the wire cutters to cut off any excess wire coming out the end. Then file off any excess solder so the connector pin will not jam in the socket. Them slip the sleeve over the plug and screw it down. The plug is now ready to use. A final precaution would be to check the plug with an ohmmeter to make sure it's not shorted by a loose strand of wire.
Skinny coax requires a sub-diameter adapter. It slips over the cable and screws into the plug. RG-8-X and RG-59 are different diameters, so they require different adapters.
In using an adapter, slip the adapter over the wire before starting to work on it.
The adapter will come to within about a sixteenth of an inch of the insulator inside the plug. Take off some outer layer from the coax and peel the braided copper back over the adapter. It will have to be unraveled to do this. Then strip the inside insulator off the inner conductor, leaving about a sixteenth of an inch beyond the end of the adapter. Tin the center conductor so it will hold together. Then insert the coax into the plug and screw the adapter in. Solder the center conductor into the plug tip and then melt solder through the four holes and into the pushed-back braid, soldering the braid to the plug. Finish up by trimming the wire sticking out of the tip, filing any excess solder off the tip, and screwing the sleeve onto the plug body.
This job is kind of a pain in the neck, but once the plugs are installed on the coax, it's a dream to connect and disconnect.
You can purchase lengths of coax with connectors already installed, but this is not always convenient. If you want to run a coax through a floor, it's best to drill a hold just big enough for the coax, and install the connector after the coax has been threaded through the hole. Also, the finished coax might not be available in a convenient length.
For receiving, skinny coax is adequate. Usually RG-8-X is preferable to RG-59. Up to about 300 watts, skinny coax is satisfactory for transmitting. With more power, the bigger coax is necessary. I prefer RG-213/U over RG-8/U. The RG-213/U is more expensive, but it has a better braided shield and has less line loss.
Coax needs to be treated with some respect. Avoid sharp bends or kinks--they can damage the coax internally. Coax can be buried underground, but that will shorten its life, nobody knows for sure how much. Skinny coax with its foam insulation is most vulnerable when buried. RG-213/U is about the best underground. Coax will last longer underground if its protected by some old garden hose or plastic conduit pipe. Burial without protection is not recommended, though coax may last for a number of years when buried directly. Hams do it all the time.