THE SKIN EFFECT
PROPERTIES OF COAXIAL CABLES
A coaxial cable has various electrical properties, which we will explain briefly here. They are decisive for the selection of the best cable for the respective application. There are, among others:
The attenuation of the cable, i.e. how much a signal is weakened- The impedance, the effects of alternating current resistance of the cable
- Other measurements such as shielding, velocity factor, maximum permissible power, etc.
Typical values for the losses of a coaxial cable range from about 30 dB/100m at 144 MHz (high attenuation) to less than 4 dB/100m at 144 MHz (low attenuation).
Especially for reception, we are dealing with extremely low signal levels. Therefore, the attenuation is one of the most important selection criteria of a coaxial cable. Yet, the cable with the lowest attenuation is not always the best, because who can drill holes several centimetres thick in the wall to lay cables as thick as an arm? So it comes down to a sensible compromise between attenuation, ease of installation, weight and price. And - you should always keep the cable as short as possible.
The better the cable, the denser the braiding of the outer conductor. Cables that use an additional foil on top of the braiding achieve the best shielding. Such cables have up to 100 dB or more shielding. However, these foils make the assembly of the plug a little more complicated, more on this later.
Cables with a solid inner conductor are often better suited for high power, but they become heavier. To compensate for this disadvantage, a solid wire made of aluminium is often used, which is coated with copper on the outside for better conductivity. This is sufficient, because -> see skin effect. If you want to lay a cable for a rotatable antenna around the rotor, both cable types (stranded, solid wire) work. Stranded cables are somewhat less problematic; this also has something to do with the connector, more on this later.
A BRIEF INTRODUCTION TO INDIVIDUAL CABLE TYPES
(incomplete selection)
RG-58
The RG-58 cable is one of the best known and most commonly used cables. It has an outer diameter of 5 mm and is quite flexible. This makes it suitable for many applications, even where you have to run it in tight places. However, the attenuation of RG-58 is very high and there are enough modern alternatives (H-155, Aircell-5, Airborne-5) with double shielding, much less attenuation and other better properties. So it is easy to switch to these better cable types for new installations.
RG-213
The approx. 10mm wide RG-213 is available in many versions, recognisable by additional letters after the designation such as RG-213CU-MIL-C17 or similar. The cable is very popular because of its robustness and high availability (= low price). It is almost only used on shortwave for high power applications, because for VHF it has too high attenuation.
Ecoflex-10, Ecoflex-15
The Ecoflex-10 cable from the German manufacturer SSB Electronic is very popular because it meets the highest quality standards. It is double-shielded, has relatively low attenuation and is also quite light. This makes it suitable for use up to the WLAN frequency range, and on the 2m and 70cm amateur radio bands even over longer lengths.
The cable is also available in other variants, for example as Ecoflex-10 Plus (lighter, higher cut-off frequency) or as Ecoflex-10 Plus Heatex with flame-retardant properties for public buildings. The thicker variant Ecoflex-15 (15mm outer diameter) has a significantly lower attenuation once again. There is also an Ecoflex-15 'Plus' version.
Ultraflex-10, Ultraflex-13
The manufacturer Messi & Paoloni puts a lot of effort into the production of high quality coaxial cables in their own production facility in Italy. The 10mm cable Ultraflex-10 can be used up to 6 GHz and is sufficiently flexible due to its stranded inner conductor. Double shielding is part of the quality standard anyway. The cable is also available in 7mm and 13mm diameter versions.
WHICH CABLE FOR WHICH APPLICATION?
When it comes to cables and plugs, the most expensive is not automatically the best. It has to fit the application. We have already given some hints, on shortwave higher power levels can normally be handled than on VHF/UHF/SHF, but in the higher bands low attenuation is crucial. Both lead to cables with larger diameters, but some series like Ecoflex or Aircom are especially optimised for high frequencies up to 6 GHz or even 12 GHz, others like Aircell rather for shortwave and VHF. GSM/LTE/5G as well as WiFi require cables with low attenuation on higher frequencies, the transmitted power can be neglected because it is usually very low for consumer applications.
SOLUTIONS OFFERED BY WIMO
This article has introduced you to the technical characteristics of a coaxial cable, and briefly outlined which of them are most important for us radio amateurs. We have also presented different cable types and use cases to help you choose the right cable.
WiMo offers a wide range of coaxial cables, from standard types to very high quality cables made in Europe as well as special cable types. On our website, you will find the full range of products, various filters help you to make your choice. For example, you can choose by diameter, as this often determines the possible applications (size of the hole in the wall, visibility, weight etc.).
If you do not want to equip the cable with plugs yourself - please use the service of WiMo. In addition to a very large cable warehouse in Herxheim, we also stock a wide range of connectors. Several state-of-the-art cable machines from Schleuniger (Switzerland) and well-trained employees help us to produce customised cables quickly and accurately in Germany. At competitive prices, with the high speed of a local supplier.
The WiMo cable configurator also helps you with your selection. Here you simply choose the two connectors and the length (to the cm) - and you will get a list of coaxial cables with all variants WiMo can offer. Including price and delivery time!
At high frequency - and this is already the case on medium and short wave - the current is forced to the surface of the wire by induction. As a result, copper or silver plating of wire or stranded wire lowers the losses. The inner part can even be made of less good conductors such as steel or aluminium and thus becomes mechanically more stable.
Stranded wire can also carry more high frequency currents than a solid inner conductor due to the larger surface area, it is also somewhat more flexible.
