![]() This also eliminates phase noise, and the third and fourth effects can be minimized by internal adjustment and temperature compensation, respectively. Weak coupling, the second effect, is most dominant, so it is imperative to use a common synthesizer/LO source to stabilize the phase between two signal generators. For a 1-m copper cable (coefficient of thermal expansion 16.4 x 10 -6/K), a 10K temperature change leads to a 0.164-mm change in length or about 2 degrees of phase drift. Consequently, the wavelength will be two-thirds that in free space and the electrical length approximately 1.5 times the physical length. Thermal expansion is calculated for coaxial cables where the velocity of propagation is approximately two-thirds that of free space. ![]() For example, at 6 GHz, the wavelength is 3.3 cm, and adding only 1 mm more cable produces a phase shift of 11 degrees. This changes the electrical length of the signal path.
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