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VHF Super Regen

I'm playing with super-regenerative oscillators in LTSpice.

My question concerns the 230XP valve VHF super-regenerative oscillator in this figure 8.9:

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Here's figure 8.11 from the same book:

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The text reads: "the super-regenerative oscillator in figure 8.11 is a triode valve connected in a commonly used high-frequency circuit of the Hartley type which relies on the internal capacities of the valve for its operation." Why is it a Hartley when the tap is fed through an RFC?

Does the 230XP oscillator in figure 8.9 also rely on internal valve capacities? How do these oscillators work? What is special about tuning capacitor C in figure 8.11? What is the role of the cathode chokes?

I've been playing with JFET oscillator circuits in LTSpice and I can't get them to oscillate unless the LC network between drain and gate creates a phase inversion. How do these valve circuits make 0 (or 360 degrees) of phase shift around the loop?

What is the nearest semiconductor equivalent of the above valve circuits? Below is a JFET oscillator with feedback from drain to gate; but no reliance on parasitic capacities, although I'm sure they affect the frequency. Is this an LC Pierce?

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TIA Andrew.

Reply to
Andrew Holme
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I'm wondering if they're actually common-grid oscillators relying on anode-to-cathode parasitic capacitance. This circuit oscillates:

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Reply to
Andrew Holme

A very perplexing circuit. I'm not sure the original author of this circuit completely understood how it actually worked either! There are at least two plausible mechanisms for the RF feedback, the plate-cathode feedback from inter-element capacitances, or plate-grid feedback from the tank itself through the unmarked capacitor to the grid.

I think the feedback mainly comes from the capacitor to the grid from other side of the tank. (ie a Hartley oscillator) That cap is just a DC blocker I believe. You could probably replace V1 with a JFET and the circuit would work fine without a drain-source feedback capacitor.

The RFC in the cathode circuit is to prevent C1 from shunting the RF on the cathode. This makes the plate-cathode feedback more likely, especially as the plate circuit is floated by its own RFC. I have no idea of the properties of a CV6 tube so I can only guess what is really going on.

The cathode circuit looks very much like it is a self-quenching circuit, but the diagram below suggests it is separately quenched? This is an IFF transponder? The feedback loop is interesting, looks like reflexing to me. I'd guess the entire circuit oscillates at the quench frequency and the modulation is recovered by filtering that output?

I've always wanted to build a toy walkie talkie from a similar circuit. Super-regen on RX and AM on TX by changing the source and drain circuits on T/R.

--
Alan Yates
http://www.vk2zay.net/
The Moon is Waning Crescent (17% of Full)
Reply to
Alan Yates
[snip]

It's an IFF responder and it's separately quenched. When lit by radar, it emits a pulse of characteristic duration and much stronger than a passive reflection.

The book also contains examples of the same oscillator circuit but without the cathode choke i.e. grounded cathode.

Reply to
Andrew Holme

Aha, that came form the unique (and now quite rare) book "Super-Regen receivers" by JR Whitehead.

Without knowing what the RFC value is, it's hard to say what type of oscillator it is.

There were thousands of super-regens built in the 1960's and 70's using transistors, often OC170 and OC171, for radio control, door openers, alarms, early CB sets and the like. I have a lot of schematics somewhere.

There has been some more recent work done on super-regen receivers, One was in QEX Sept-Oct 2000.

Barry

Reply to
Barry Lennox

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