The Dope On Radio Connectors

The most important and weakest link in a good radio setup is the cable and cable connectors. Make sure you follow good practices and don't skimp on quality or procedures. Connecting a radio to an antenna isn't all that hard if you follow some basic rules.

1) Use good quality connectors. Even some from China are ok

2) Use good coaxial cable

3) Use good practice installing connectors on the cable

4) Insure any exposed connectors are free from moisture and rain

5) Secure cables so they don't slap against any hard surfaces in the wind

Let's take these one at a time.


Connectors

Connectors will have one of three outside finishes. Chrome, nickel, and silver plated. Chrome is shiny and very good for being exposed to the elements, however they should be taped up securely to prevent water from entering the connector and cable. More expensive connectors have a silver plating and are excellent for indoor use. Silver plating will eventually tarnish but it won't affect its performance. The center insulation should be teflon for lower loss. Older bakelite insulators have a brownish look and are sufficient for frequencies under 30 mhz. The center conductor is either silver plated or gold plated for a better connection. You can purchase most of these connectors here.

There are only a few types of connectors used for Amateur Radio (Ham), SWL, CB, GMRS, or Business band radios. These are "UHF" style, PL259 male and SO-239 female.


PL-259 male connector


SO-239 flange mount


SO-239 on back of Ham radio transceiver. "UHF" style are used in most radios or transceivers from 150 mhz down to 2 mhz.

Notice the insulator that surrounds the center pin is white. This usually means it is made of teflon and can handle higher frequencies and temperatures and is unbreakable. Earlier insulators were made of Bakelite and were brittle and not efficient at higher frequencies.


Bakelite or composite plastic insulator

The term "UHF" connector is a misnomer. In the early days of radio, anything above 40 mhz was considered UHF and this connector was the industry standard so anything above 30 mhz was considered UHF, so the name. As we ventured into much higher frequencies, actual UHF, no incentive was made to rename this connector so it is still named UHF today.

 

BNC connectors are smaller and are a twist lock as shown below.


These BNC male connectors are shown attached to coax cable

 


BNC female flange connector usually found on the backs of radios


Some smaller portable HF transceivers have the BNC antenna connector on the side of the radio

N Connectors,


N female flange


N Male cable end

For high performance and low loss, UHF and microwave frequencies, you will see N type and SMA connectors used. Pictures show gold plating on these N connector center pins.


SMA type connectors

 

R-SMA or RP-SMA connector (reverse polarity) is shown on left picture. Usually found on Chinese imports. Standard SMA is picture on right.

Most operators use an adapter to go from SMA or R-SMA to BNC so they can use standard coax cable or after market whip antennas. Adapter is shown below.

 

Many times you may find that the cable connector isn't the same as your radio connector. In this case you can use adapters to connect the cable to the radio. Some are shown below.

 

 

There are a few other obscure types of RF connectors but they are rare and you will probably never come across them.


Coax

Coax is short for coaxial cable. It is a shielded cable with a center conductor. It comes in just a few types. RG174, RG8, RG8X, RG58, RG213, LMR200, LMR400, LMR600, LDF4-50. Each has a specific use. All are 50 ohm impedance. Cables such as RG59, RG11, and RG6 are 72 ohm cables and are primarily used in cable TV and video systems and are not suitable for radio communications.

The LMR and LDF series are high performance low loss cables normally used in commercial applications. They are considered 100% shielded with either an aluminum shield or copper shield. Coax cable is also rated by the amount of signal loss at higher frequencies. This is a link to a list of cables and their losses. For typical home use you will not need to use these cables because of their cost unless you operate at UHF frequencies and long cable lengths. Cable length has a lot to do with losses too. Losses are referred to as DB, percent, or -gain. That is, a hundred feet of RG8X has a loss of 3.6 db per hundred feet or 46% efficiency, or a loss (gain) of .46.

RG8X is the most common for frequencies under 150 mhz and lengths of less than 100 feet. A cutaway is shown below left.


Shown is the solid copper center conductor, then the white foam insulation followed by the copper braid and the outside black insulation jacket

Below is a cutaway of a LMR series cable

 


Attaching connectors

Care and skill is required to install connectors on the cable. There are numerous Youtube videos showing how to install connectors and there are websites showing cutting charts and procedures. One thing to remember is that some connectors require you to install the shell or strain relief and shrink tubing on the cable first before you crimp or solder the connector center pin.

Some connectors only need a crimping tool to crimp the center pin and outside compression sleeve. Conventional connectors require you to solder the center pin and mechanically compress the braided shield to the connector housing itself. A piece of heat shrink tubing over the cable and shell crimp will help stabilize the cable so it won't kink, and provides a level of protection from water getting in.

It is a good idea to ohm out the cable to make sure there is no short from center conductor to braid and continuity from center pin to center pin, and shield to shield.

Cables can be purchased with connectors already installed and are available on Ebay or other retailers. They usually come in lengths of 1, 2, 5, 10, 50, and 100 foot lengths. Some vendors will customize lengths if desired.


Protecting connectors and cable from water

When permanently mounting the cable and antenna, it is important to make sure no water will enter the cable through the connectors. A very generous amount of good vinyl electrical tape by stretch wrapping the connector and a few inches down the cable is important. Water will find a way in if you are not careful. Once water is introduced into the cable it almost always destroys the cable and no amount of drying will help. Copper braid will oxidize and turn black and will no longer make a good electrical and RF contact. You can also find self-sealing tape that will fuse together providing air tight protection. You may also find a tar like tape that makes a permanent seal. In both cases it is wise to first put a layer of electrical tape over the area to be sealed, then place the tar or self fusing tape over it. This will make it much easier to remove the fused tape if you need to remove disassemble the connector.


Securing the cable

When installing a cable feed, make sure the cable is secured with high quality 3M black vinyl electrical tape at least every ten feet. This will keep the wind from slapping the cable against metal or brick thus preventing breakage of the outside insulation and allowing water to enter. Do not use black Tywraps (cable ties or zip ties) . Even though they claim to be sun, weather, UV resistant, they will get hard and snap in just a few years.


For more information on connecting your radio to an antenna please visit this page.

 

Copyright 2021 by Rick C. Ver 0.13 Jan 26, 2021