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Cables, Cable manufacturing

THE SKIN EFFECT

What is that?
Knowledge Box

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.
The attenuation
The attenuation of a coaxial cable results from the lossy, physical properties of metallic conductors. In concrete terms, this means that a signal is weakened, it arrives with a lower level after transmission via the cable than at the Tabellenblatt1 Explorarbeginning. The following simple rules apply: thicker coaxial cables attenuate less than thin ones, the attenuation increases with the frequency. So actually "more is better " is correct for thicker cables in this case, or more precisely: less is lost because the distance between the sheath and the inner conductor is higher and thus the losses in the dielectric are lower (the dielectric is the area between the inner and outer conductor). Further, the attenuation is frequency-dependent, i.e. it increases with rising frequencies. That is why a good (= low attenuation) cable is especially important on VHF (2m and higher). The attenuation is given with the dimensionless factor decibel (dB), more precisely "x dB attenuation per 100 m cable length". 3 dB attenuation would mean a factor of 2, i.e. a loss of 50%, 6 dB reduced by a factor of 4 (only 25% arrive), 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 impedance
In commercial radio technology as well as in in amateur radio, coaxial cables with an impedance of 50 ohms are most common today. In television technology, 75 Ohm cables are very often found. The value is basically the ratio of the diameter of the inner conductor to the distance of the outer conductor. Cables with a higher impedance usually have a lower attenuation, but are thicker in proportion. The value of 50 ohms was chosen because this is a good compromise between loss and the impedance of the antennas and other devices to be connected. The impedance cannot be influenced by the user, so all you have to do when choosing is make sure that the impedance is 50 ohms. This is the correct value for amateur radio, as well as for almost all WLAN, mobile radio, Lora and other antennas.
The shielding factor
The outer conductor of a coaxial cable is usually made of a braid of thin copper wires. Inexpensive cables use relatively few wires here, so the shielding effectiveness is low (around 60 dB). The shielding factor describes the shielding of the cable to the outside. This effect is interesting in two directions - a good shielding protects against radiation to the outside and prevents interference in systems (TV, network, etc.). Similarly, a good shielding protects against interference from outside on the received signal.
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.
The power
Thicker cables permit higher power - not only because of the lower attenuation, but also due to a higher permissible voltage, because the distance between inner and outer conductor is larger. The dielectric heats up less due to losses. Therefore, only a few watts should be transmitted via a thin cable of the type "RG-174". A thin cable feed-through at the window is no problem for a satellite reception cable, but less recommendable for a cable coming from a power amplifier.
The velocity factor
In free space, high-frequency waves travel at almost the speed of light. This is completely different on a cable! Here the propagation speed is much lower, usually around 60 to 70% of the speed of light in a vacuum. This value is important when I use a coaxial cable to specifically delay a signal with the help of the cable length. This is done, for example, with so-called phase cables, which interconnect several antennas. Or with a balun that acts as a transformer to match the impedance of an antenna to the cable impedance. Another application is a filter made from a short piece of coaxial cable. Cut to the right length - taking into account the velocity factor - it is possible to build very inexpensive bandpass filters, for example to filter the broadcast band.
Construction of the inner conductor
There are two ways to construct the inner conductor of a coaxial cable: as a stranded conductor made of many individual wires (litz wire) and as a solid inner conductor made of one wire. Both have advantages and disadvantages. A cable with a stranded wire is usually more flexible. The more wires the strand uses, the better the flexibility and the larger the surface, see skin effect. However, the manufacturing effort increases and the cable becomes more expensive.
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.

Shortwave up to 6m, low to medium power
Standard cables such as RG-213 are suitable here. If you want the lowest possible interference, you should use a double-shielded cable such as Aircell-7 or Ultraflex-7.
Shortwave up to 6m, high power
For higher power RG-213 is still suitable in many cases, otherwise a good 10mm cable is required. So Ecoflex-10, Ultraflex-10 etc.
VHF, FM operation (relay, marine radio, professional radio)
FM operation on VHF does not necessarily require the highest quality cable, the levels are usually sufficient to get by with thin 5mm cable. Use H-155, Aircell-5 or Airborne-5, if you are looking for the best price RG-58 might be enough. However, the length should not exceed 10 m.
VHF SSB (Weak Signal Modes)
Radio amateurs with directional antennas for 2m and higher want to cover the longest possible distances, so the signals are correspondingly small. Here, every dB counts and so you should not save on the cable. The lengths should be kept as short as possible. Popular cables in this area are Ecoflex-10, Ecoflex-15, Ultra/Hyperflex-10 and Ultraflex-13. For extreme lengths, you have to try to get a very high-quality piece of cable from a commercial system on the second-hand market, such as Cellflex or other ‘hardline’ cables with large diameters.
Wifi, LoRa (Helium Miner)
For these applications, the focus is on the higher frequency ranges, i.e. 868 MHz (LoRa, Helium) or 2.4 or 5-6 GHz for Wifi. So here it really depends on the attenuation of the cable. But, again one often needs to make a compromise decision, because the widely used mini connectors of Wifi devices are not available for the thick cables. This means that you are often forced to work with cable adapters (so-called pigtails). The best is to look at the entire distance and calculate what is better - thick cable + adapter or thinner cable without adapter. Mostly 10 mm cable is used, for long distances > 10m sometimes thick Ecoflex-15 and then adapted to the respective device with a 20cm long pigtail.
Active antennas for short wave and VHF
Active antennas, which are only used for reception, have an amplifier built right into the base of the antenna. The output level is usually very high and with some antennas even adjustable. This allows you to save on the coaxial cable to the receiver and use the simplest and thinnest cable you can find - at these high signal levels, the attenuation does not matter very much. Extreme cable lengths of 100m or more are possible. For mechanical reasons, however, one does not use the very thin RG-174, but RG-58 or similar.
Special applications
Sometimes you need a cable that can handle a lot of power, but in a very small space. This is the case, for example, when winding baluns or for internal cabling. Here, cables with a particularly resistant dielectric, namely Teflon, are the best choice. These are then cable types such as RG-316, RG-142 or RG-400.

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!

Configure your cable here

WHAT IS THE SKIN EFFECT?

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.

Items 1-10 of 154

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  1. Ultraflex-10 Coaxial Cable
    Bestseller
    Ultraflex-10 Coaxial Cable

    10.3mm outside diameter, double-shielded, 4.8 dB/100m @144MHz.Cable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

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    As low as: €4.75
    incl. VAT, plus shipping €3.99
  2. Ecoflex-10 Coaxial Cable
    Ecoflex-10 Coaxial Cable

    LowLoss coaxial cable with 10.3mm outer diameter, very suitable for VHF/UHF, flexible with stranded inner conductor, double shielded.Cable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

    View accessories
    As low as: €6.20
    incl. VAT, plus shipping €5.21
  3. H-155 Coaxial Cable
    H-155 Coaxial Cable

    Low loss coaxial cable, outer diameter 5.5 mm, double shieldedCable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

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    As low as: €1.30
    incl. VAT, plus shipping €1.09
  4. Ecoflex-5 Coaxial Cable
    Ecoflex-5 Coaxial Cable

    LowLoss coaxial cable with 5.5mm outer diameter, very suitable for VHF/UHF, double-shielded, extremely flexible and low bending radius.

    In stock, shipped in 1 to 2 days

    View accessories
    As low as: €2.40
    incl. VAT, plus shipping €2.02
  5. Ultraflex-7 Coaxial Cable
    Ultraflex-7 Coaxial Cable

    Coaxial cable with 7.3mm outer diameter, double shielded, stranded inner conductor, low attenuation.Cable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

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    As low as: €3.00
    incl. VAT, plus shipping €2.52
  6. Aircell-7 Coaxial Cable
    Aircell-7 Coaxial Cable

    Coaxial cable with 7.3mm outer diameter, foamed dielectric for low attenuation, double shielding. German manufacturer SSB Electronic.Cable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

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    As low as: €3.80
    incl. VAT, plus shipping €3.19
  7. Ecoflex-7 Coaxial Cable
    Ecoflex-7 Coaxial Cable

    LowLoss coaxial cable with 7.3 mm outer diameter, very suitable for VHF/UHF, double-shielded, extremely flexible and low bending radius

    In stock, shipped in 1 to 2 days

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    As low as: €4.65
    incl. VAT, plus shipping €3.91
  8. RG-58 Coaxial Cable
    RG-58 Coaxial Cable

    Proven coaxial cable with 5mm outer diameter, ideal for station cabling for powers up to 200 W, large selection of suitable connectors.Cable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

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    As low as: €0.90
    incl. VAT, plus shipping €0.76
  9. Aircell-7 Heatex coaxial cable, flame retardant
    Aircell-7 Heatex coaxial cable, flame retardant

    Coaxial cable with 7,3 mm outer diameter, flame-retardant and low-smoke, suitable for laying in public buildings, double-shielded

    In stock, shipped in 1 to 2 days

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    As low as: €4.20
    incl. VAT, plus shipping €3.53
  10. Hyperflex-5 Coaxial Cable
    Hyperflex-5 Coaxial Cable

    Coaxial cable with 5.4mm outer diameter, very low attenuation due to air foam dielectric, flexible.Cable Impedance 50 Ohm

    In stock, shipped in 1 to 2 days

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    As low as: €2.30
    incl. VAT, plus shipping €1.93

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