# What Do You Need to Know about Power Calibrating

It is complicated to calculate the rated power for RF phase stable cables. During application process, sufficient calculation by professional engineers is necessary, yet inconvenient. Focusimple Electronics has made a detailed instruction of the cable rated power, specifically as follows.

**First of all, What is the rated power of the RF phase stable cable?**

When the cable can safely and continuously transmit RF signals within the applicable frequency range, and there is no insulation overheating or thermal breakdown caused by insulation overheating, the allowed power capacity is the rated power of the cable.

By definition, the "temperature" will be the crucial factor influencing the rated power.

**The principal factors that affect rated power are divided into internal(self) and external factors.**

**Internal factors:**

**a.The maximum operating temperature of the cable**

**b.Attenuation and VSWR of the cable**

These parameters of internal factors are inherent criteria of the cable, which had been solidified during design and production. In general selection, the lower the attenuation of the cable, the higher the power it can withstand; the higher working temperature the cable can resist, the higher power it can withstand; the lower VSWR of the assemblies, the higher power it can withstand.

The cable datasheet of Focusimple Electronics has indicated the maximum allowable operating temperature of the cable, as well as the attenuation and power of different frequencies.

**External factors**

**c. Environmental temperature**

**d. Altitude**

**e. Frequency**

The influence of these parameters on power is the most commonly mentioned in actual use.

**Environmental Temperature**

The Environmental temperature directly affects the cooling capacity of the cable, and thus directly affects the power of the cable. In Focusimple Electronic cable datasheet, the power is the normal value at 40℃ in standard environment, and the power at other temperatures can be calibrated according to the temperature factor (℃) in Figure 1.

Figure 1

**Altitude**

When the cable is utilized at high altitude, as the height increases, the air becomes thinner and thinner, so the surface heat dissipation becomes more and more difficult, and the rated power decreases. The change of altitude and atmospheric pressure can be converted, as shown in Figure 2. The pressure value lower than the standard atmospheric pressure (101.325kPa) is also called vacuum degree. Different vacuum degrees can also be found in Figure 2.

Figure 2

In Focusimple Electronics cable datasheet, the power value is the nominal value at standard sea level, and the power at other altitudes can be corrected according to the height coefficient (CH) in Figure 3.

Figure 3

Generally speaking, the rated power decreases as the frequency increases, and the relationship between the two is more complicated, but for Engineering applications, the attenuation is inversely proportional to the power, which can be approximately conversed by the following formula.

**α1P1=α2P2 （Formula 1）**

In the formula, α1 and P1 represent the attenuation and rated power at frequency f1, and α2 and P2 represent the attenuation and rated power at frequency f2. For the attenuation of different frequencies, please refer to the cable datasheet of Focusimple Electronics, and then calculate according to formula 1.

The final corrected power Px is calculated as follows:

**Px= P×CT×CH （Formula 2）**

In the formula, P is the standard power in the Focusimple electronic cable datasheet, CT is the temperature factor, and CH is the altitude factor.

Take the FSB-500 cable of Foucsimple Electronics as an example. The datasheet is shown in Figure 4 below. Find out how to calculate the final power of this cable at a frequency of 6GHz, an ambient temperature of 50°C, and an altitude of 10,000 meters.

Procedure：

- Check Figure 4, thestandard power at 6GHz in the FSB-500 datasheet power is 0.35kw;
- Check figure 1, thetemperature coefficient CT = 0.9 at 50℃; check figure 2, the altitude coefficient CH =0.67at 10km;
- Calculate the approximatepower at the target state in accordance with Formula 2.

Px= P×CT×CH=0.35×0.9×0.67=0.21kw