|
|
|
|
|
Directional Apparatus for use with High-Frequency
Transmission Lines. Tjiske Douma, Sierra Electronic Corp. San Carlos, Calif. US Pat. # 2808566, Oct 1 1957. Application Jan 12 1953. This Patent describes a bridge using a toroidal current-transformer based on suitable magnetic material such as "Ferrite", with capacitive voltage sampling network and LF compensating resistor. The transformer is loaded with low value resistor to reduce effect of winding capacitance and secondary inductance. Design equations are given. An optional LF compensating resistor also provides DC path for detector, e.g., a "crystal rectifier". Douma appears to have achieved his invention by building the lumped-equivalent circuit of the Sontheimer-Korman coupler US Pat. # 2423416 (Cited as prior art). Carl Sontheimer was later to patent just about every other possible directional coupler configuration imaginable (US Pat. # 3426298). Douma's circuit is often mistakenly described as a 'Bruene Bridge', after the article: "An Inside Picture of Directional Wattmeters", by Warren B Bruene W0TTK [later W5OLY], QST April 1959 p24-28. Bruene's bridge similar to the Douma bridge, but is rearranged for use with a shunt-diode detector and lacks LF compensation. Bruene's design appears to be a patent workaround. The floating detector port makes control of parasitics difficult, and LF compensation should always be included. Hence Bruene's circuit should be regarded as obsolete since the expiry of Douma's patent in 1977. Note that Douma's work relates to the field of long and medium-wave broadcasting. The problem of neutralising the circuit for HF radio purposes is investigated in Ch6 Appendix 6.4 and 6.5. An extension to Douma's directional coupler design (compensation for generator-side capacitance) is given in US Pat. # 2734169. |
|
Cited or related references: USP 2423416 Sontheimer and Korman 1947. USP 2467648 Alexander 1949. USP 2734169 Douma 1956. USP 2285211. Korman 1942. Radio frequency Wattmeter [uses capacitive voltage sampling with compensation resistor]. |
|
|
|
|