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Radio Broadcast
HOW DESIGNERS HAVE AVOIDED REGENERATION
THE neutrodyne was probably the first adequately sensitive receiver which did not to a greater or less degree transmit, but the neutrodyne, as no regeneration is employed, is somewhat wasteful on tubes. By this, 1 mean that a five-tube neutrodyne does not get anything like the volume from its five tubes that it would, if regeneration could be employed in the three radio-frequency tubes.
Regeneration is also a tremendous aid to selectivity. It can be regarded as an application of negative resistance. As regeneration is increased, the effective resistance of the circuit becomes less and less until it reaches zero. If pushed to, or beyond, this point, oscillation occurs.
You all know that a low resistance circuit is a "sharp" or selective circuit. The neutrodyne owes its selectivity not to the individual selectivity of each circuit, but to what is called the concomitant selectivity of the three circuits involved. For instance, if each circuit reduces interference to 10 per cent, it will be 10 per cent, in the first circuit, i per cent, in the second and ,V of i per cent, in the third. Approximately the same selectivity can be obtained in fewer circuits by making them of lower effective resistance by using regeneration.
There are several types of receivers which
manufacturers have developed to escape regeneration. The Teledyne, which is illustrated in the accompanying photographs is a recent contribution in this line. The Teledyne makes use of full regeneration in the detector, but even if the detector is allowed to oscillate, these oscillations cannot be radiated because of the peculiar type of radio-frequency amplifier ahead of the detector. The Teledyne with four tubes under equal conditions seems to have somewhat more volume than the five tube neutrodyne.
The grid and filament of this radio-frequency amplifier are connected in the usual manner across the antenna tuning inductance. The plate of this tube is coupled to the detectorgrid inductance, which is tuned with the usual parallel condenser. The detector is furnished with a conventional regeneration coil commonly called a "tickler." The coupling between these two tubes is such that when the detector-grid circuit is resonant, this circuit has an impedance approximately equal to the output impedance of the amplifier tube, which is the correct load for most efficient output of this tube. In this coupling position, the impedance is not of the correct inductive value to produce oscillations, so that the radiofrequency amplifier cannot itself oscillate. Its grid inductance, which is in the antenna, is at zero coupling position to the detector-grid inductance (primarily to prevent parasitic feed
COMPLETE CIRCUIT DIAGRAM OF THE TELEDYNE RECEIVER It uses one stage of radio-, two stages of audio-frequency amplification, and detector