Regenerative Receivers Using Capacitive Feedback
Regenerative Receivers Using Capacitive Feedback
Some time ago, regenerative receivers using capacitive feedback through the internal plate to grid capacitance of a vacuum tube triode were discussed here.
This thread and the references therein left some questions regarding the feedback mechanism and the important issue of feedback control unanswered. This paper here is presented in the hope that it will provide answers to at least some of the open questions.
For further reference, the abstract section of this paper is quoted below.
The design concept of a regenerative receiver using a capacitive feedback path back into the grid
tank is well known because is was used in the first regenerative receiver design patented by E.H. Armstrong in 1913. As opposed the the more prevalent inductive feedback employing a "tickler coil", capacitive feedback in most cases relies on the internal plate to grid capacitance of vacuum triodes and requires no external components to complete the feedback path. Most intriguing with capacitive feedback is the issue of exercising feedback control. Since the internal plate to grid capacitance of the triode in use cannot be altered, feedback control needs to be implemented by an adjustable tuned plate tank in the regenerative RF amplifier stage. The two basic plate circuits here are the parallel LC plate tank and the series LC plate tank and we will analyze the behavior of regenerative RF amplifier stages based on capacitive feedback for both of these by deriving equations valid for an arbitrary LC network in the plate circuit. As is turns out, the parallel LC plate tank typically offers an abundance of positive feedback but suffers from a highly sensitive feedback control and has a very pronounced detuning effect on the grid tank. The series LC tank, in contrast, offers a very fine-grained feedback control with less detuning but there may be circumstances where it might not have enough positive feedback reserves.
Attachments:
- Cfeedback_rel.pdf (383 KB)
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