Difference between revisions of "Coax Cable for Ham Radio Applications"

Latest revision as of 16:17, 30 December 2016

Selecting the right cable for your radio transceiver installation is a balance between three primary factors:

1. Signal Loss
2. Cable Flexibility
3. Cost

In a perfect world you would have a relatively thin cable that was a perfect impedance match, well shielded, suffered from little to no signal loss, and was so flexible as to easily bend around tight corners and to the back of your transceiver. In the real world, no such cable exists. Everything is a compromise, the customary trade-off as with anything in life. The best shielded cables on the market are thick, lack flexibility, and are very costly. Cheap low-end CB radio cable is very flexible but loses signal readily. Signal loss is exacerbated as frequency is increased. Such signal loss is not as much of a problem in the HF radio bands as it is in the VHF and UHF bands. So, there's a lot to consider when purchasing cable for your mobile installation or a tower run into your ham shack.

In addition to cable signal loss, there are other issues to consider. Connector loss is another factor. SO239/PL259 is perfectly suitable for HF installation, including CB radio, not lossy when used on UHF installations. Cable durability is another factor. Your outdoor cable installation has to endure sunlight, the elements, and in some cases, squirrels and other critters. Mobile installations can often take even more abuse, especially under vehicle body cable runs (which should be avoided as a general rule.) Yes, you truly have a lot to consider when selecting the right wire for your transceiver signal fire. Power capacity, (if you are running an amp) may also become a factor.

Coaxial Cable Index

RG-59 or RG-6 should not be used for ham (75ohm TV)

RG-58 (CB cable) has a high loss factor in VHF and UHF frequencies, so it really only is useful in runs less than 50 feet for frequencies above 100 MHz, and 20 feet for frequencies above 400 MHz.

RG-8U is great for 50-75 foot runs in the VHF/UHF range.

UR67 or RG213 for 70cm.

LMR-400, Belden 9913 for 100 feet + in 70cm amateur radio, or GMRS.

RG8, RG8X, RG58U

RG58U

• more flexible
• solid center conductor
• lower cost
• good for short runs with mobile installations
• Outer Diameter: 0.200 inches

RG8

• less loss on long runs 50ft - 100ft
• thicker and less flexible
• Outer Diameter: 0.405 inches

RG8X (mini foam)

• smaller than RG8 with less loss than RG58U
• stranded center conductor
• still not as good as RG8
• Outer Diameter: 0.240 inches

NASA Coax Cable Loss Chart

RG-58 has an impedance of 50 ohms. Types are labeled RG-58 or RG-58/U. These cables have a solid center conductor. The second type is RG-58A/U and they have a center conductor made up of many thin wire strands.

RG8/U and RG8A/U has been obsoleted and RG213/U is the modern replacement. Both RG213/U and RG214/U are considered military specification cable. This is very rugged cable and a popular choice among amateur radio operators. However, the cable begins to be noticeably lossy at higher frequencies. A 50ft run of RG213 for the 2m ham band is perfectly acceptable. A 100ft run of RG213 for the 70cm ham band is ill advised.

Comparing RG8X and RG58: They are both the same diameter. RG58 is more flexible. RG8X has slightly less signal loss. In a mobile installation any loss below 1GHz is inconsequential.

RG213

RG-213/U is a low-loss, 50-ohm Coaxial Cable with a non-contaminating PVC jacket.

• Outer Diameter: 0.405 inches

There is a type of cable labeled 90-19213 which is nearly identical to RG-213. It is one of many "clone" cable types hitting the market in recent years.

RG213 is good for use on HF frequencies with cable runs up to 100ft without suffering any appreciable loss. It is not ideal for the VHF band and absolutely a poor choice at 70cm. The loss becomes significant as you increase frequency, it should not be considered for use above 220MHz.

LMR-400

• Outer Diameter: 0.405 inches

Also called Times Microwave, LMR400 has a copperclad aluminum center conductor. LMR400 is often considered a modern replacement for older Belden 9913. LMR400 is lighter in weight and easier to manufacture. It is also more flexible making it somewhat easier to work with. However, at most frequencies the Belden 9913 has a tiny advantage in slightly less loss compared to LMR400. The LMR400 dielectric is basically foam which makes it more rugged than Belden 9913. Basic LMR400 has a solid center conductor. The more expensive Ultra Flex LMR400 has a stranded center conductor.

Comparing LMR400 to the inferior RG213 you will probably not notice a difference in loss on the HF bands for lengths less than 100 ft. For runs at 200 ft then you will start to notice where LMR400 outperforms RG213. At frequencies at and above the 2m ham band the difference becomes far more noticeable.

Belden 9913

• Outer Diameter: 0.405 inches

Belden 9913 has a solid copper center conductor. The dielectric of Belden 9913 is a thin tube of polyethylene and a thin spiral of polyethylene holding the center conductor in place. This makes it slightly less lossy than LMR400, however, the difference is not really significant.

Belden 9913 and LMR400 have a .405 inch outer diameter with a #10AWG center conductor, and takes ordinary Amphenol connectors like 83-1SP (UHF male). The center conductor of Belden 9913 and LMR400 is slightly larger than RG213.

More modern is the Belden 9913F7, which uses 10 AWG stranded (7x19) .108" bare copper conductor and gas-injected foam HDPE dieletric insulation. This makes it more competitive with LMR400. The "F" is the indicator of a "foam" dielectric. If the designation is LMR-400 UF then the U indicates it is UV resistant, which withstands better in direct sunlight.

Belden 9913 F7 is a low loss flexible foam dielectric with a VP (velocity Factor) of 85%.