RF cable for LTE antennas

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Updated – January 25, 2024

Good HF cables for connecting LTE antennas to routers are essential for optimal reception and transmission performance, as are all the connectors used. In general, the thicker the better, but also more expensive.

Now, as always in life, it is important to find the best compromise between price and performance. The data to be taken into account when making your selection is explained below.

Framework conditions

First of all, it is important to research the general conditions. How long does the cable have to be, what maximum bending radii are possible when laying it?

In the stationary environment (house, property) the distance to the transmission tower does not change. So you can start from the reception field strength given according to the distance to the transmission mast and, if necessary, accept longer cable routes or “worse” quality cables as long as the reception still corresponds to the desired level.

In mobile use, you should always assume the worst possible conditions and therefore choose the shortest cable routes and the best cable and connector qualities, with inevitably larger bending radii.
However, the cables that are usually permanently installed on the antennas are up to 5 m long, which on the one hand is suitable for almost any installation, but on the other hand relieves you of the agony of choosing the right cable. Partly to the chagrin of those who would like to be “optimally” equipped.
Anyone who uses antennas that are delivered without permanently connected cables can meet this goal to the fullest.

Cable structure

Dielectric and shielding

A high-frequency (HF) cable consists of an inner conductor that transmits the signal, a dielectric (an oxygen-rich, white PE plastic. The softer, the more oxygen is trapped in the pores of the plastic, and the larger the permissible bending radius ( in order to avoid crushing of the pores). Furthermore, the cable contains at least one, if necessary several, wire braid(s) that shield from interference radiation and/or electrically conductive CU foils.

Bend radius

The bending radius is the smallest possible radius due to insulation technology in which the cable can be laid “around the corner” without damaging the internal HF insulation layer(s). The best insulator would be air. Since this cannot be achieved in a cable, the above-mentioned plastic technology is used.
In addition, the shielding foils must be protected from tearing if they are bent too tightly, which also requires a larger bending radius. Braids are more tolerant in this regard.

Sheath material

The outer PVC jacket, usually black and possibly UV-resistant, is intended to protect the cable from environmental influences and mechanical damage.
Halogen-free cable jackets are fire-safe and are therefore preferred for use in residential environments because, in the event of a fire, they produce less smoke and no harmful halogens, such as bromine, chlorine, fluorine or iodine, or their acid gases.

Cables equipped in this way meet the conditions regarding:

• Flammability according to IEC 60332-1
• Acid gas development according to IEC 60754-1 / 60754-2
• Smoke development according to IEC 61034-2

Shielding

A good cable is characterized by a shielding attenuation of at least around 100 dB. In environments with high electromagnetic interference potential, additional standing wave barriers made of ferrite cores are recommended. These are assembled with around 20 pieces per cable by sliding them over the cable. They are available in different inner diameters. Common diameters are, for example, 4.95 mm / 7 mm / 10.3 mm.

The choice of cable should therefore also be based on the dimensions of the ferrites that may be necessary and are commercially available.

RF cable and data

Here is a list of commonly used RF cables in descending order of attenuation values. Data sheets are available by clicking on the respective cable type in the first column.

Here are technically identical SSB cables of type ECO flex x, not listed separately FRNC, or. HEATEX differ from the listed types only in that they are halogen-free.

Table Plugin

Antenna gain above all else?

From a user perspective, it is ideal to have the highest possible antenna gain in order to achieve the best data transfer rates. If you compare the worst with the best HF cable, the difference is, depending on the antenna gain, up to a tenfold increase in (router) transmission power (3 W instead of around 0.32 W)!

The legislator (Order 59/2009 Official Gazette of the Federal Network Agency No. 20/2009 dated October 21, 2009), however, limits the transmission power EIRP (equivalent isotropically radiated power) to 25 dBm, approximately 0.32 W.

Most routers allow a legally compliant setup of the EIRP at 23 dBm via the country settings. This means that a reserve of 2 dBm is taken into account. The choice of antenna and cable determines whether these limit values are adhered to or significantly exceeded.

Antenna Gain Theory

The gain information for antennas suggests amplification. However, that is not the case. An antenna does not amplify anything because it is a passive component and only transmits transmitted or received power.

But: a directional antenna can absorb more energy from the direction in which it is aimed (thereby supposedly amplifying it) and has a radiation pattern in the form of a more or less stretched lobe.

A rod antenna, on the other hand, has the (theoretical) radiation characteristics of a sphere, receives and transmits in all directions. A “wave” appears on the antenna rod like a sine wave, with three zero crossings and a wave crest and trough. The maximum deflection of this curve is considered the antenna gain.

Component choice

A combination of 6 m Air cell 5 Cable, the antenna LGAM-7-27-24-58 with 5 dBi gain in the 2,600 MHz range produces a permissible transmission power of 24.55 dBm at 0.29 W.
However, the same antenna only has a gain of 2 dBi in the ranges up to 800 - 1,600 MHz and, with the same type of cable but only 1 m cable length, emits an identical transmission power of 24.71 dBm of 0.3 W.
However, if you use the original 6 meters in this frequency range, the transmission power is only 23.23 dBm, corresponding to 0.21 W!

In order to achieve approximately the same transmission power with the same cable length, you would have to use the cable instead of Aircell 5 EcoFlex 15 use and would achieve 24.43 dBm or 0.28 W.

If you want to exploit the maximum transmission power (within the permitted limits) in all frequency ranges, you will not be able to avoid working with different cables (attenuation factors). This results in: the better cable for 800 - 1,600 MHz, the worse for 2,400 MHz.

calculation

By entering the respective values of the specific application into the yellow fields in the table below, the relevant parameters are automatically calculated and output in the green fields.
Regarding the attenuation values of the cable, note the desired frequency (800, 1,600 or 2,600 MHz), as the attenuation increases with increasing frequency.

If the EIRP value is displayed with a red background instead of green, the limit value of 25 dBm has been exceeded, which is specifically stated in the field below.
In this case, either a cable with higher attenuation or a longer cable length or an antenna with lower gain must be used in order to comply with legal regulations.

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Cable laying

As long as cables are to be laid behind skirting boards, in cable ducts or false ceilings, bending radii are relatively uncritical. In a motorhome, space is tighter and bending radii are more of an issue. Window feedthroughs are usually implemented with a “flat” cable approximately 20 – 40 cm long, which inevitably results in higher attenuation losses and should only be used if there is absolutely no other option.
A recommended cable is, for example, the one from Cable master.

As stated at the beginning, bending radii should not be exceeded in order to avoid impairment of the electrical properties of the cable. Even a short-term “kink” inevitably leads to the irreversible destruction of the dielectric at this point.

Extensions

You should avoid cable extensions, as each plug connection results in attenuation losses, which are included in the calculation of the EIRP and must be compensated for by higher antenna gains.