In spring 1931 Zavoisky was sent to Leningrad to the Central Radio Laboratory of the Komintern Plant, where he pursued thorough research of superregenerator. There he also designed ultrashort-wave (cophased) generator. Here is an extract from Zavoisky's report about his work in CRL: "…The experimental work, done in the Ultrashort-Wave Laboratory, consisted in the following:

1. I. Research on superregenerator:
2. Common resonance shape of superregenerator;
3. Mechanisms of resonance shape of superregenerator;
4. Necessary and sufficient condition for superregenerative hiss mode;
5. Relationship of superregenerative hiss and different parameters of superregenerator;
6. Separate generation and modulation;
7. Explanation for superregenerative hiss and superregenerator sensitivity. The report to be published is based on the researches.

1. II. Together with P.M.Vinnik, a staff member of the Ultrashort-Wave Laboratory, we designed new schemes for generation of short and ultrashort waves, which can be characterized in general as following:
2. The circuits let obtain waves shorter than usual with the same valves;
3. Due to the circuits the efficiency increases up to 40-50%;
4. The circuits provide the growth of generator power by valves connection without wave-length changing;
5. Some operating modes of generator are characterized by extremely high harmonics.
6. III. Together with P.M.Vinnik we developed a new type of valve receiver, characterized by the absence of typical detector, which functions are performed simultaneously by generator and the transmitting triode".