It’s one of the most frequently asked questions on forums, in Facebook groups, and at gatherings: Which coaxial cable is best for my antenna installation? The answer is that many types of coaxial cables are good by default; it just depends on what you expect from them. Do you want to minimize signal loss? Will the coaxial cable often be exposed to wet environments outdoors? Is it for a one-time installation?
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Coaxial cable build up
All coaxial cables are fundamentally composed of four parts.
The core
The core (or center conductor) is a metal wire that carries the radio frequency (RF) signal. It’s usually made of copper, either stranded or solid. Sometimes, steel or aluminum is used instead. Steel cores are found in coaxial cables that can withstand heavy mechanical stress, while aluminum is more often used in budget coax cables.
Since RF tends to flow on the surface of the core, copper cores are sometimes coated with a thin layer of silver, and steel or aluminum cores are sometimes coated with a layer of copper. This silver or copper layer reduces loss, although on HF and short coax lengths, this difference iisn’t noticeable in practice. Silver-coated coax is more commonly used at UHF and higher frequencies.
The dielectric
Around the core is an insulating plastic dielectric. The most commonly used material is solid polyethylene (PE), as in popular RG-58 and RG-213. It’s affordable, durable, but rather heavy and not very flexible. PE foam is also frequently used; it’s lighter, flexible, and provides less signal loss. Sometimes, an air chamber is added between the core and the dielectric to further reduce loss. However, this air chamber can fill with moisture, leading to SWR issues. For such coax cables with air chambers, N-connectors (or better) are often used, sealed with self-vulcanizing tape.
PTFE or FEP (also known as Tefloin is also used as dielectric. These plastics withstand high temperatures and heavy mechanical stress.
The shielding
All coaxial cables have shielding, usually a copper braid, sometimes tinned for extra corrosion protection. To prevent interference from external sources on the core, some coax cables have double braiding or an additional layer of copper or aluminum foil.
The jacket
The jacket of the coaxial cable protects it from external influences, primarily from the weather. The jacket is almost always plastic. Polyethylene (PE) and polyvinyl chloride (PVC) are most commonly used. PE is highly UV-resistant but permeable, meaning moisture can penetrate the jacket over time. The thicker the jacket, the less permeable it is. PVC is less permeable, sturdier than PE, but UV-stabilized PVC coax jackets are still prone to becoming brittle over llong time from UV exposure. However a lifetime of 10 years is achievable.
Coax jackets are also made of PTFE or FEP, which are mechanically strong, non-permeable, and resistant to aging.
Signal loss
Every type of coaxial cable has signal loss, though the differences can be significant. Popular RG-58C/U has about 7.1 dB loss over 30 meters at 150 MHz (2-meter band). The thicker RG-213/U has 2.6 dB loss at the same frequency, while LCF158, a very thick coax used in cell iinstallations, only has 0.24 dB loss.
So, what’s a good choice? There’s a substantial price difference; LCF158 is about 20 times more expensive than RG-58. However, investing in low-loss coax is worthwhile, especially for VHF and higher frequencies, where losses are significantly higher than for HF.
A rule of thumb is that on HF, a few dB of loss isn’t disastrous. On VHF and higher, it can make a difference unless you’re only making local connections. But it would be stupid to invest in a 3000 Euro or US Dollar RF amplifier, when most of the power is lost in the coax.
Maximum power
The maximum power a coaxial cable can handle depends on the type of coax and frequency. The maximum power capacity decreases as frequency increases. The thickness of the coax iisn’t a determinant for maximum power; it’s a combination of core material, dielectric, and dimensions.
For example, the PE version of RG-58 (5mm diameter) can handle a maximum of 300 W at 100 MHz, while the FEP version RG-316 (2.5mm diameter) can handle 375 W at the same frequency.
Aging
Most types of coax don’t age quickly, but if you’re installing coax for long-term use, remember that it won’t last forever. Aging occurs in two main ways, moisture and ultraviolet.
- PE: Due to permeability, moisture eventually migrates through the jacket, causing corrosion in the shielding. Aluminum foil shielding corrodes fast due to galvanic corrosion. Avoid using PE-jacketed coax in very wet environments. However, PE is ideal for full sun exposure.
- PVC: More sensitive to UV light, which breaks down plasticizers in PVC, causing brittleness and eventually allowing moisture to penetrate. Due to minimal permeability, it’s ideal for wet environments or even lying in a pool of water on a roof. The black color of PVC jackets slows down aging. If you choose PVC, mount the coax on the shaded side of the mast. PVC becomes stiff at low temperatures.
- PTFE/FEP: Completely resistant to aging but has mechanical and cost drawbacks.
Galvanic corrosion caused the coax aluminium foil shield to turn into aluminium oxide powder.
Fixed installation or flexible use?
If you reuse coax frequently, such as for field days, POTA, or SOTA, flexibility is very useful. However, many flexible coax types have foam dielectric, which, if heavily kinked, can cause the core to touch the shielding or even break the core entirely.
A solid core isn’t recommended for flexible use as it can break after frequent bending. For flexible use, a PE dielectric combined with stranded wire is highly suitable, such as RG-58, RG-213, RG-214, and RG-223.
Coax and antenna rotor
Using an antenna rotor requires extra caution, as the rotation causes variable stress on the coax. Types with a solid core aren’t suitable for rotor use, and coax with foam dielectric and foil shielding is also less suitable. A safe choice is coax with a PE dielectric and stranded wire (RG-58, RG-213 or RG-214). Sometimes, solid PTFE or FEP coax, like RG-400, is used for the final stretch from below the rotor to the antenna.
Price
Coaxial cable prices vary significantly. PTFE or FEP coax costs about five times as much as PE dielectric coax. In general, better specs come with a higher price tag.
Practical tips
- Using coax with foil shielding outdoors? Choose copper foil and avoid aluminium.
- Avoid running coax through standing water; if unavoidable, choose a PVC jacket.
- If the coax is constantly exposed to sunlight, choose a PE jacket or run the coax through a PVC pipe.
- For flexibility, choose coax with foam dielectric.
- If the coax is frequently moving, such as with an antenna rotor or for POTA or SOTA, choose coax with a solid dielectric.
- For the final segment high in the mast or hard-to-reach areas, consider PTFE or FEP coax for its extrreme durability. You’ll never have to replace it again.
My personal choices
For HF use, I’m a fan of 7mm coax variants with double shielding (braid and copper foil). These offer an excellent balance of price and performance, with minimal loss even over lengths of 20-30 meters. Types like Aircell-7, H-2007, Ultraflex 7, HF2500, and RF287UF have similar specs.
For VHF and UHF, I use the same variant but in 10mm coax, which has lower loss at these frequencies. Types include Ultraflex 10, RF400UF, Hyperflex 10, and Airborne 10.
Finally
I’ve seen plenty of (beginner) radio amateurs who, when building their antenna installation, didn’t account for the cost of coaxial cable in their budget. That’s a shame, because if you consider the cost of good coaxial cable, it can bring you years of enjoyment—up to ten years or more. So, don’t save on the coaxial cable!
For tips on how to chose ham radio equipment, read this article.