Super-Regenerative Receivers

[lfarrand]

I came across the super-regenerative receiver and found it very interesting, especially when considering how to build large voltages in a circuit. It reminded me somewhat of Tesla's magnifying transmitter & receiver. Could this be combined with an avalanching diode as the RF source signal?

Circuit



From: http://www.r-type.org/articles/art-285.htm

If a tenth of a penny had been invested at 5% per annum compound interest in the year 1 AD it would today have grown to £100,000,000,000,000,000,000,000,000,000,000,000,000 or roughly a lump of gold as big as the whole world for every 10 seconds through all those years. As the super-regen amplifies on the same principle, a phenomenal gain is only to be expected. Its voltage amplification is limited at one end by the size of the smallest possible voltage (i.e., noise) and at the other by the power-handling capability of the valve, and is of the order of a million. That is assuming the oscillations have time to build up to the limit. The lowest QF that does not cut into speech frequencies is, say, 10 kHz, so half a cycle lasts 50 μS. judging from the examples already worked out, it looks as if we ought to allow for several hundred RF cycles in this time; say 500. That puts the lowest RF for most effective performance at about 10 MHz (30 metres wavelength). The lower the RF, the stronger should be the quench oscillation, in order to build up within the limited number of RF cycles.

On the other hand, if the RF is very high and/or the quench is very powerful, it is better to increase the QF, in order to get more build-ups into a given time. The QF giving the most amplification is that which just allows time for full build-up and die away in each of its cycles.


From: http://www.r-type.org/articles/art-293.htm

While on the subject of FM it may be worth mentioning that a super-regenerative stage has been found very effective as an amplifier. I have not actually tried it in this role, but suggest it as an interesting line of experiment to follow the set just described when its possibilities have been exhausted. The theory, briefly, is that a super-regenerative oscillator is synchronized by an incoming signal of as little as 10 microvolts. Being modulated by the quenching, the oscillator has a series of sidebands spaced at intervals of fq (the quenching frequency), so each of these is frequency-modulated by an incoming FM carrier. If fq is considerably higher than the frequency deviation of the carrier - say 200 kHz - so that any one sideband can be selected to the exclusion of all others, it can be applied to the usual FM discriminator (Fig. 4). In practice it appears to be necessary to use a frequency - changer to lower the frequency of the super-regenerative output. And a buffer stage is desirable in front to prevent radiation. So it begins to approach the orthodox superhet in complexity. But with an equivalent amount of gear it seems likely to have a higher sensitivity and freedom from ignition interference. (The ordinary FM receiver is not too good at coping with the latter; but a super-regenerative stage in front ought to reduce it to manageable proportions.) Whether you ultimately go, in for this fancy hybrid or stick to the plain superhet, however, the single-valve super-regen. is a good introduction to the VHF band.

By no other means is it possible so easily and so cheaply to obtain first-hand knowledge of what is still terra incognita to many wireless men.


Interesting waveforms

[Vasik041]

Tesla's Colorado Sprigs Receivers

http://teslasociety.com/teslarec.pdf

[lfarrand]

Tesla's Colorado Sprigs Receivers

http://teslasociety.com/teslarec.pdf

Very interesting, thanks for sharing that.

[F6FLT]

The idea was very interesting in the old days, since by looping part of the output back to the input, the gain of a single tube or transistor amplifier could be increased because the signal passed through several times, at the same time the selectivity increased because the feedback favored the tuning frequency.
Of course the main problem was the triggering of autoscillations, and when radio hobbyists in the 30/40's had their antennas close together, they would interfere with each other.
The reaction is not limited to the electronics, it also puts energy back into the antenna. This is a positive effect for reception, and not well known. The energy re-injected into the antenna opposes the received ambient field. The ambient field around the antenna decreases, but since the energy is conserved, this field energy is found in the input circuit of the receiver. So it is as if the antenna is acting on a larger volume of space around it, recovering more energy.