1. M. E. Zhabotinskii and Yu. L. Sverdlov, Foundations of the Theory and Technology of Frequency Multiplication [in Russian], Izd. ?Sovetskoe radio,? Moscow (1964).
2. A. Ya. Rotshtein, Author's Certificate No. 124004 (1958);
3. Bulletin of Inventions No. 22 (1959).
4. A. G. Pinchuk, Author's Certificate No. 67166 (1946);
5. Bulletin of Inventions No. 9 (1946).