Test of Radio Frequency Amplifiers

Abstract

The prescnt paper is a resume of the test results obtained by the authors for the various type of high frequency amplifiers. For the wave length longer than 3000 meters, the selective or the non selective character may be obtained at will with the suitable design of amplifiers. By the use of audio-transformer sheets which from the closed magnetic path for the auto-transformer, a very good character can be given for the non-selective auto-transformer amplifiers. The amplifiers designed gives practically constant amplification for wave length from 5000m to 25000m or from 3000m to 10, 000m. It is shown that audio-transformer sheets may be also employed for the non-selective type amplifiers.
For shorter wave length, the non-selective type amplifiers must be abandoned since they are not efficient enough. To increase the amplification per stage, one of the following method must be employed.
(a) The coil of low-loss type must be employed.
(b) Care must be taken to reduce the effect of the capacities included in parallel with the plate impedance.
(c) It is sometimes necessary to reduce the effective resistance in the plate tuned circuit of the initial stage amplifier by feeding back the amplified voltage into the input side of this initial stage. (reaction)
Typical examples obtained with reaction for the resistance and the transformer amplifiers are given. Some practical remarks are also given, which may be useful to get the Stable working and the maximum amplification for the predetermined value of the wave length.