[600MRG] building the ultimate regenerative receiver

[kl7aj at acsalaska.net]

I've always had a regenerative receiver or two lying around the shack. Since I'm getting into 630 meters, I thought I'd build a new regen for that band, just for jollies.

Contrary to a lot of literature out there, all regenerative receivers are not the same. Some of the newer versions, such as MFJ's are pretty good, but there's room for improvement. A lot of the later designs are based on the assumption that "a little positive feedback covers a multitude of sins." While true in theory (the autodyne function is indeed capable of infinite gain and sensitivity, regardless of the open loop parameters), in practice this is not the case. After playing around with a LOT of regen receiver designs, here are two truths that make all the difference in performance.

1) Use the HIGHEST Q tank circuit possible. Do NOT rely entirely on "Q-multiplication" to make this work. A decent regen receiver will work "reasonably well" without any regeneration.

2) Design the RF amplifier to have the highest OPEN LOOP gain possible. You only need a gain of slightly more than 1 to make an oscillator oscillate....this is NOT the best idea for a regen receiver. Again, the receiver should work "fairly well" before adding any feedback/regeneration. In an attempt to make modern regens "user friendly" i.e., not touchy, manufacturers have been using gain control, such as by adjusting the bias or adjusting the emitter resistor value, to created some degeneration. This practice SERIOUSLY degrades performance. The old school "tickler coil" method for adjusting regeneration is STILL the superior method....by a long shot. Yes, it's touchy....but when you get the hang of it, the magical regen performance of ages past really comes to life.

In the near future, I will present some oscilloscope shots of my optimized 630 meter regen.
Stay tuned!

Eric
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Eric P. Nichols, KL7AJ
AlasKit Educational and Scientific Resources
3763 Lyle Avenue
North Pole, AK 99705
(907) 488-0483
(907) 371-7120
http://alaskit.co