Attenuation vs Temperature

Attenuation Vs Temperature

The temperature, also affects the attenuation of the cable (dB). Also in this case, with modest temperature ranges, the variation is negligible, but if you move far away from the reference temperature (in this case 20C° / 68F°), this can lead to variations remarkable by the more scrupulous operators. If you want to know the variation of attenuation related to temperature, multiply the attenuation value by the K4 coefficient, shown in the graph 4.

 

Rapporto Attenuazione/Temperatura - Attnuation/Temperature Ratio

 

Fattore Temperatura K1 - Temperature Factor K1

 

The Power Handling is calculated at the temperature of 40°C/104 F° (tested directly on the surface of the cable itself) and the variations in more or less, are leading to a decrease or increase of this value.

 

Another factor to consider, is the impedance matching of the system. If not optimal, it generates stationary waves (VSWR). At low to medium values (1 - 1.5), these do not substantially modify the power handling, but at higher values, the cable has to withstand both the incident power and the reflected one. Consequently the power handling drops. In the GRAPH 2, the coefficient K2 is obtained (VSWR), which multiplied by the value of the Power handling declared, provides the maximum allowed power for the VSWR tested in your line.

 

Coefficiente ROS - Coefficient VSWR

 

It’s interesting to know that even the altitude interacts with this data: the higher you climb in altitude, the more the heat dissipation decreases. The graph N3, provides the coefficient K3 related to altitude.

 

Fattore Altitudine K3 - Altitude Factor K3

 

It must also be considered the type of Rx-Tx transmission (RTTY or SSB). Physical accidental alterations and excessive VSWR values (impedance mismatch), are certainly increasing the lost power dissipated in the form of heat. Moreover unwanted stationary waves ratios, are making the situation even worse. In SSB operations a 5/6 seconds transmission time, followed by the same reception lag, is giving the chance to nearly double the power handling values. Be aware that the power should never be exceeding the declared peak power value.

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