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I'm planning to build a two-tube reflexed RF regen receiver soon. I'm examining methods of controlling the regeneration — it needs to be possible to both initiate and halt oscillation in all bands (I plan to cover 500 kHz to 30 MHz, if I can manage it).

what I keep reading as the "best" method of controlling regeneration is sometimes called a variometer or variocoupler — the tickler coil is mounted on a pivot, so it can rotate from aligned with the tuning coil (or in this case, the secondary of the RF coupler between the RF amp and detector), to opposite, so the field from the coil goes from maximum positive feedback to maximum negative feedback.

I've been mulling over for a couple weeks how to do this without the physical moving coil (which seems prone to issues in a portable set). It came to me that I can use a double length tickler with a center tap, connect the arm of a potentiometer to the detector plate, and connect each end of the potentiometer track to one end of the tickler, with the return through the center tap.

Split Tickler Regen Receiver

This ought to allow me to vary the feedback continuously (if not linearly) from maximum negative to maximum positive without any mechanical parts. What I'm uncertain of is whether the resistance that's always in the circuit (except at maximum positive or negative setting) will have a negative effect on sensitivity or tuning width.

I can't find any reference to this method of controlling regeneration -- have I invented new, 85 year old technology, or was there a good reason this wasn't done?

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  • $\begingroup$ I'm reading up on variometers now. This is interesting stuff! What about fixing the inner coil to be colinear with the outer, but then adjustably delay the current through the inner coil? You could even have multiple delay lines that you add up before inserting into the inner coil, leading to multi-band tuning $\endgroup$ – Marcus Müller Aug 1 at 14:26
  • $\begingroup$ the terms tuning and filtering kind of blend over for me – tuning means adjusting the properties of an antenna so that at the right frequency, it's got the right impedance, and much energy is passed from æther to receiver only for the selected frequency. Filtering means adjusting the properties of a system so that only energy of the selected frequency is passed through the system. But my understanding doesn't really matter here, it's your question after all :) $\endgroup$ – Marcus Müller Aug 1 at 14:51
  • $\begingroup$ so, you want to build a filter, right? $\endgroup$ – Marcus Müller Aug 1 at 14:52
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    $\begingroup$ Ah I can see now: the variometer also fulfills the coupling job $\endgroup$ – Marcus Müller Aug 1 at 15:18
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    $\begingroup$ Let us continue this discussion in chat. $\endgroup$ – Zeiss Ikon Aug 1 at 15:38

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