Editing Direction finding (section)

==== Klystron and TWT preamplifiers ====
The klystron and [[Traveling-wave tube|TWT]] are linear devices and so, in principle, could be used as receiver preamplifiers. However, the klystron was quite unsuitable as it was a narrow-band device and extremely noisy<ref name = Beck />{{rp|392}} and the TWT, although potentially more suitable,<ref name = Beck />{{rp|548}} has poor matching characteristics and large bulk, which made it unsuitable for multi-channel systems using a preamplifier per antenna. However, a system has been demonstrated, in which a single TWT preamplifier selectively selects signals from an antenna array.<ref>Kiely D.G., "Advances in microwave direction finding", Proc. IEE, Vol. 113, No.11, Nov 1964, pp. 1967–1711</ref>