Coaxial cable is a type of electrical cable designed to carry radio frequency (RF) signals from one point to another with minimal interference. The "coaxial" part refers to the fact that both the center conductor and the outer shield share the same axis — they're nested inside one another, like pipes inside pipes. The name sounds technical, but the idea is simple: keep the signal-carrying wire in the middle isolated from external noise and from leaking its own signal outward. For amateur radio operators, selecting the right ham radio coax cable is fundamental to achieving optimal station performance and maximizing signal efficiency.
Key Specifications: Impedance, Frequency Response, and Power Handling
For ham radios, most options are 50 ohms, which are ideal for high-powered applications while delivering low loss. This impedance matching is crucial for efficient power transfer between your transceiver and antenna. The impedance mismatch between 75Ω coax and 50Ω radio equipment creates a 1.5:1 SWR. This causes about 4% of power to be reflected — often acceptable, especially considering RG-6's advantages, though 50-ohm coax remains the standard for amateur radio applications.
Frequency response varies significantly between cable types. Loss increases with frequency, which is why a cable that's perfectly adequate for HF can be a serious problem on VHF and UHF. Understanding this relationship helps amateur radio operators choose appropriate coaxial cable for their specific operating bands.
All three of these cable types will handle 100W or more at frequencies below 500 MHz, which covers most ham transceivers. If you are running more than 100W, you should check the power specification of the cable you are using. Power handling capabilities decrease with frequency, making proper cable selection critical for high-power operations.
Common Coax Cable Designations and Naming Conventions
The RG prefix on cable stands for "Radio Guide," the original military specification for coax cable. The number that follows the RG was just a page in the radio guide—it has no other significance. The RG designation is just a general description of coaxial cables that are available. Modern cable designations like LMR (Land Mobile Radio) represent evolved specifications designed for lower loss and improved performance.
At one time, RG-58, RG-8X and RG-8U were military standards but now these terms are used rather loosely and refer primarily to the size of the cable. Accordingly, I added "type" to the term to indicate that it is not a precise standard. The LMR (Land Mobile Radio) cable terminology is becoming popular in the amateur radio world, so the corresponding LMR designator is shown in the table (LMR-200, LMR-240, LMR-400).
Difference Between Solid and Stranded Conductors
Cables with solid center conductors are less flexible than those with stranded center conductors. The dielectric material and the outer insulating jacket can also affect the flexibility of the cable. For portable operations, I always buy cable that is rated "flexible" because it is easier to handle and deploy. This choice impacts both installation flexibility and long-term reliability, with stranded conductors offering better flexibility at the expense of slightly higher loss in some cases.
Popular Ham Radio Coax Cable Types
RG-58: Applications and Limitations for QRP Operations
RG-58 U is the most commonly used coaxial cable in the amateur radio community. It is a versatile and affordable option that can handle frequencies up to 1 GHz, making it suitable for many ham radio applications. RG-58 U is typically used for short runs of less than 100 feet, although longer runs are possible with proper termination techniques. This flexible cable is about .195 inches OD with a single braided shield. It's typically used for lower power applications, short patch cords, and mobile installations. The small diameter allows it to fit into tight spaces typically found in vehicles. Because of the relatively short cable distances involved in mobile installations, losses are minimal.
RG-58 (50 ohm) is about 0.195", quite lossy, suitable only for mobile installations (typically < 20 feet, < 150 watts). For QRP operations where power levels remain low, RG-58 provides an economical solution for short runs, particularly in portable and mobile applications where flexibility matters more than minimal loss.
RG-8 and RG-213: Heavy-Duty Options for High Power
RG-8U type is about twice the diameter of RG-58 and RG-8X and it's the general purpose coaxial cable, best for long cable runs in HF and VHF. RG8 is a thicker 50 ohm cable, at 12 AWG, that can provide a stronger signal than RG58. It is mainly used for amateur radio. These larger diameter cables handle significantly more power and exhibit lower loss characteristics compared to smaller alternatives.
For example 100 feet of cable at 156 MHz: RG-8: 2.4 dB loss RG-8X: 4.3 dB loss LMR400: 1.5 dB loss, demonstrating the performance benefits of larger diameter cables for longer runs and higher frequencies.
LMR-400 and LMR-600: Low-Loss Alternatives
The LMR series represents a modern evolution in coax design. Where traditional RG cables use plain braided shields, LMR cables use bonded aluminum foil and tight braids that dramatically reduce signal loss — sometimes 30 to 40 percent lower attenuation than an equivalent RG type. The foam polyethylene dielectric and bonded foil plus braid construction give it loss figures roughly 2.2× better than RG-58 at 144 MHz and 2× better at 440 MHz.
LMR-400 sits in the middle of the LMR range, handling longer runs in commercial and industrial environments where RG-8 would lose too much signal and RG-11 is overkill. For those who require even higher power handling capabilities, there's the LMR-600 series cable. This type of cable has a much larger diameter than either the RG-8X or LMR-400 and can handle up to 10,000 watts of power.
RG-174 and RG-316: Miniature Coax for Portable Operations
RG-174 (50 ohms) is very small (~0.11") and lossy. Suitable only for short pigtails and jumpers at very low power, as in receivers, scanners, etc. These ultra-small diameter cables serve specific applications where space constraints outweigh loss considerations, particularly in portable equipment interconnections and test setups where flexibility and compact size are paramount.
Cable Loss and SWR Considerations
Understanding Attenuation and Loss per Frequency
All coaxial cables will attenuate the signal as it travels down the cable and the signal loss can be significant. For example, just 3 dB of signal loss means that you've lost half of the transmit power as it propagates down the line. This loss applies for both transmit and receive… you'll have less power out to the antenna and less signal showing up at the receiver. A 3 dB loss means half your power is wasted as heat in the cable. On VHF and UHF, where cable loss increases significantly with frequency, choosing the right cable can make the difference between a strong signal and a marginal one.
The 146 MHz loss through 100 feet of this cable is 1.5 dB, or 0.9 dB better than ordinary RG-8U. A loss of 1.5 dB means that we still lose 30% of the power. If we use our 100-foot run of LMR-400 on the 20m band (14 MHz), the loss is only 0.5 dB. This means that 90% of our signal power makes it through the cable.
How Cable Length Affects Signal Loss
Cable loss scales linearly with length, making proper calculation essential for longer runs. Here's how much power from a 100-watt radio reaches the antenna after 100 feet of each cable type at 144 MHz and 440 MHz: At 440 MHz, RG-58 delivers only 20 watts out of 100, illustrating the dramatic impact of frequency and cable choice on power delivery.
For a 50-foot VHF/UHF run, the extra $40 for LMR-400 vs RG-58 buys you approximately 3.8 dB more signal — nearly a full S-unit on receive, and the difference between a solid contact and a lost one. Understanding this relationship helps operators make informed decisions about cable investments.
SWR Impact on Coax Performance
Coax, oh the other hand, is very lossy at high SWR. Mismatch loss is the additional power reflected back due to an imperfect impedance match (SWR > 1.0). In practice, moderate SWR (under 2:1) adds relatively little additional loss — usually less than 0.5 dB. Important: This additional loss is multiplicative with the cable's base loss. A lossy cable with high SWR compounds the problem. The good news: Below 2:1 SWR, the additional loss is minimal and usually not worth worrying about.
Loss Calculations for Different Ham Bands
Modern coax loss calculators provide accurate assessments for various frequency bands. Times Microwave Systems has a very handy online calculator for coaxial cable specifications, which I used for the calculations in this article. You can use the Times Microwave System calculator to try out different combinations of cable length, cable style and operating frequency. These tools allow operators to optimize their feedline choices based on specific operating requirements and frequency allocations.
Selecting Coax for Different Ham Radio Applications
HF Operations: Balancing Cost and Performance
For the right applications it's excellent: it's flexible (minimum bend radius of about 1.5 inches), inexpensive, and at HF frequencies the loss difference versus premium cable is negligible for short runs. Specific situations where RG-58 is the right call: HF operation (below 30 MHz) with runs under 40 feet. For longer HF runs or when pursuing maximum efficiency, the HF ham antenna on my roof is connected to my transceiver using LMR-400. Many would say this is silly, because there is not a lot of difference between cheaper RG-8 or even RG-58 and the better LMR-400 at HF frequencies.
RG-8X: This .242 inch OD cable is extremely popular in the Ham radio community primarily because it's super flexible, relatively low loss, and fairly inexpensive. It's good for HF applications up to 30 MHz at 1.2 kW and is generally suitable for runs up to 100 feet. It's also acceptable for short runs on 144/220/440 MHz, especially in mobile applications.
VHF/UHF Considerations and Requirements
Smaller diameter cables are OK for short runs, portable/mobile use, or for low frequency antennas. At VHF/UHF frequencies, and for long cable runs, larger diameter cables will always be a better choice. The higher frequencies used in VHF and UHF operations make cable selection critical for maintaining signal quality.
Use it up to 50 feet in length for HF. I would use it up to 25 feet in length at VHF, and probably even shorter for UHF. This guidance reflects the increasing importance of low-loss cable as operating frequency increases.
Microwave and Weak Signal Work Cable Needs
For microwave frequencies and weak signal operations, premium low-loss cables become essential. LMR-600 is the low-loss heavyweight for runs over 100 feet in critical RF links — donor antennas for cell signal boosters, ham radio antenna feeders, or point-to-point data links. These applications demand the lowest possible loss to maintain signal integrity across long paths or at extremely high frequencies.
Portable and Emergency Communication Setups
Portable operations require balancing performance with practical considerations like weight, flexibility, and setup speed. Portable and field day operations where flexibility and weight matter often benefit from smaller diameter cables despite higher loss, as the shorter runs typical in portable setups minimize the impact of increased attenuation.
Proper Coax Installation and Maintenance
Connector Types and Proper Termination Techniques
The PL-259 can be used with acceptable loss from the lowest HF bands right up to 100 MHz, but is often used all the way up to 440 MHz UHF as long as the coax feedline is limited to 10-15 feet like in your vehicle mount. SMA can be used with relatively low loss from the lowest HF bands, all the way up to 18 GHz. Understanding connector limitations helps operators choose appropriate terminations for their specific applications.
A poorly installed PL-
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