EXPLANATION OF THE REGEN RECEIVERS - Page 1
Forum section: electronics / rf-microwave

author: BRAVOKILO
author_rank: Newbie
timestamp: June 11, 2018, 06:45:07 am
content: The explanation of the Armstrong regens is that the signal is fed back to the grid and re-amplified. Thus regenerative. A secondary was placed in the main coil which inductively fed back the signal into the triode tube. In fact, the Super regen discussed the need for "quenching" and Armstrong solved this too. He place a second tube which was oscillating at just above human hearing(obviously so we won't hear it) which shuts down the main tube to "reset" it. The explanation is that the original signal does not disappear and "congest" the amp.Recently came across a single FET FM RX which has a free running vibrator made of two transistors which also "quenches" the FET.But more recent articles I came across (Talking Electronics) described many of its transistorized "regens" quite differently. It says that the transistor with a tank is made to oscillate very low power at a certain frequency. The feedback to oscillate it is capacitive, a cap between the C and the E of the transistor.Once a signal comes in of the same frequency, the receiver oscillator gets affected ( becomes difficult to oscillate it says) and the voltage of the coil to the rail plus line changes in accordance to the varying strength of the incoming signal (AM). The changing voltage is amplified by an audio amp.Nowhere does it talk about the received signal amplified and re-amplifed and thus does not talk about the need to quench the main osccillator. In a way, the signal does not enter the transistor at all as in the explanation of Armstrong regen. Sounds to me like when a stronger TX jams a weaker TX. The change in current draw reflects the signal but the signal is never re-amplified.I came across another explanation that "noise" initiates the Armstrong regen to oscillate. Well, in that case it is also an oscillator. And a signal appears in the surrounding, it gets affected and is picked up and fed to an amplifier.It is interesting cuz I am also reading on Direct Conversion Receivers using the famous SA602/612 originally NE by Signetics. Somehow similar. A local oscillator frequency is mixed with an incoming signal and any differential in frequency within the human hearing is heard (for CW). For SSB and AM, it says that when the frequencies are the same, known as zero beat, the IC extracts the sound. (See John Dillon's Neophyte DC receiver). The latter part on detecting SSB and AM sounds to me like the local oscillator gets suppressed when an incoming signal of the same frequency appears. The change in current draw is amplified instead of the differential frequency heard.Would like to hear from Masters around here. Thanks.

author: bd139
author_rank: Super Contributor
timestamp: June 11, 2018, 07:19:01 am
content: Never understood the appeal of a regen myself. I built one and it had terrible blocking problems. Strong signals would overload it in two seconds flat. Regen is basically a very unstable positive feedback loop. The regen control is the feedback amount and the tank defines the pass frequency for feedback. The topology doesn’t matter much for the function. Demod is usually a function of the non linearity of the amplification device. Noise is what starts all oscillations offIn the SA612 in a DC the LO doesn’t get suppressed very much at all, just the sum frequencies are so high the amplifier can’t amplify them. It is a Gilbert cell mixer that simply mixes the incoming signal with the LO and produces sum and difference frequencies. If you mix say 7Mhz with an incoming 7.001MHz signal it will output: 1Khz (difference) and 14.001KHz (sum). This is the function of multiplying the two sinusoids together. Due to the huge disparity of the signals there is usually an RC low pass filter after the SA612 in these receivers. This has a massive attenuation at 14Mhz if the corner frequency is say 10Khz. Plus the audio amp can’t amplify 14Mhz anyway. No magic there.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: June 11, 2018, 08:29:13 pm
content: There is often confusion between regen receivers and superregen receivers.They are two different things. The explanations of how they work will be different.Regen receivers are basically a transistor RF amplifier/detector stage subject to positive feedback.This increases its gain, sharpens its selectivity, and allows CW/SSB reception (if gently oscillating). They are most used on MF and HF frequencies.Why would you build one? Because they're elegant circuits. The buzz of hearing signals a world away on a single transistor. You won't get that on any other receiver configuration.Some examples:As for a superregen, that is probably the one that Talking Electronics (which specialises in small and simple VHF and UHF transmitters for **ahem** educational purposes) was on about.A superregen gets even more gain by operating at a quench frequency in the tens of kilohertz. That can be done in the same transistor as the detector or through external quenching.A superregen receiver works well for VHF AM (hardly used except for aircraft), data and broadcast FM. It's very sensitive but not very selective.Again novelty projects that show how you can achieve (sort of) many things that require multiple transistors and stages in just one or two. Examples at:

author: BRAVOKILO
author_rank: Newbie
timestamp: June 13, 2018, 01:38:14 am
content: Thanks for the invaluable inputs.Related to this topic, about the SA612. John Dillon's article on his Neophyte. He said that only for CW is the diffential frequency is relevant. Not for SSB and AM. He said that for SSB and AM, the frequency "zero beats", meaning, there is no differential! So where is the sound coming from.I can only think of the regen principle (not Armstrong's) where a local low power oscillator (the receiver's front end) gets affected by the presence of a signal of the same frequency. It's current draw would vary the voltage on the C of the tranny varies in accordance with the modulation of the incoming signal.

author: bd139
author_rank: Super Contributor
timestamp: June 13, 2018, 06:59:15 am
content: SSB is still difference product. Just the bandwidth is higher. Not sure what he is talking about.CW you’re downconverting the signal to audio and intentionally missing by 700Hz or so.SSB you’re downconverting the signal to audio and intentionally lining up the edge of the signal with the LO.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: June 13, 2018, 10:23:32 am
content: The Neophyte is different again - it's a direct conversion receiver.The local oscillator is set about 1kHz away from the frequency of the CW transmitted signal so you can hear its beat note. It can be higher or lower so there are actually two settings where you will hear the signal. You won't hear a tone if you zero beat (this position is in between the two settings).Whereas on SSB the local oscillator is set right on the frequency of the suppressed carrier so the voice comes out intelligible. There's only one setting of the tuning control where the SSB will be intelligible. If there was a carrier it would zero beat, but as there isn't the only way you know you're tuned in correctly is if you can understand what's being said.

author: mikerj
author_rank: Super Contributor
timestamp: June 21, 2018, 12:48:02 pm
content: Quote from: bd139 on June 11, 2018, 07:19:01 amIsn't the appeal achieving the maximum sensitivity with the minimum of components?

author: bd139
author_rank: Super Contributor
timestamp: June 21, 2018, 12:49:45 pm
content: Not if you have to compromise on overall performance.I can make a bike with hexagonal wheels easier than circular ones. Would I want to ride it? Hell no.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 21, 2018, 01:25:17 pm
content: Quote from: bd139 on June 21, 2018, 12:49:45 pmThey were very popular for fox hunting on 2M because they were easy to build as a group project and the performance was good enough for the purpose. You didn't even need a attenuator when getting close, just take it out of regeneration.

author: Audioguru
author_rank: Super Contributor
timestamp: June 24, 2018, 04:42:08 am
content: Regen and super-regen are used for kids' cheap remote controlled cars today, not for radios.They were used for radios many years ago when you had only a couple of radio stations in town so the poor selectivity did not cause interference. A regen radio needed you to fiddle with the regen amount control.The quenching of a super-regen provided automatic regen amount control and was used before FM stereo because of interference from the 19kHz pilot and the 23kHz to 53kHz sidebands.Morons did not notice the AM clicks and static on a regen FM radio since its sensitivity was seriously reduced by it being tuned to one side of an FM station for "slope detection".A regen aircraft receiver must not be used in an airplane or near an airport since it causes interference.A regen or super-regen radio in your home or car might cause interference to neighbours.