====== Freedom from Feedback ======

As a theoretical rule of thumb, a good decoupling requires a distance of 5 to 10 λ.(([λ] Lambda = Wave length = v/f with v∼3×10<sup>8</sup> m/s.))\\
However, in practive often a distance of 3 λ is sufficient. \\

At 2.1 GHz (e.g. UMTS) the formula returns 300'000'000/2'100'000'000 = 300/2100 = 0.14m.

Three λ will then be 0.42m i.e. 42cm.

===== GSM-R =====
For GSM-R Deutsche Bahn requires a decoupling of up to -60 dBm. According to a simulation of one of our antenna supplier a distance of 350 cm is sufficant to fulfill this requirements

Source: {{{{:faq:simulation_report_decoupling_gsm-r_v06.pdf|}}

Quelle: {{:faq:simulation_report_entkopplung_gsm-r_v06.pdf|}}