A question about the super-regenerative receiver

[listen]

Hi，

I have a question on the super-regenerative receiver. Many articles say that there is a trade-off between the sensitivity and selectivity among the super-regenerative receiver. I.e., if we increase the sensitivity, the selectivity would degrade. Would anybody clarify it a bit further?

Thanks a lot in advance!

 

[Audioguru]

A REAL radio has many tuned circuits or crystal filters for excellent selectivity, a wide bandwidth and low distortion. It has high gain for good sensitivity and has automatic gain control and good design so that strong local stations do not overload it.

A super-regen "radio" is very simple and has only a single tuned circuit that makes it have poor selectivity for strong local stations. It has positive feedback to boost the sensitivity that makes the bandwidth very narrow for weak signals and causes strong local stations to overload it.

A super-regen "radio" worked alright 60 years ago if you lived on a farm far from a city that had only a couple of not very strong stations.
Today in my city there are so many strong local stations and weak distant stations that the dial on my REAL radio is completely full of them and I cannot use a super-regen "radio".

A super-regen "radio" is an AM radio that picks up all the snap crackle and pop amplitude interference heard on an AM radio. It detects FM if it is tuned to one side of the station which causes distortion.

 

[chuckey]

I do not agree. The super-regen works by by increasing the Q of the (one) tuned circuit. So gain and selectivity increase at the same time. Can you supply any references for your statement?
Frank

 

[Audioguru]

The super-regen works by by increasing the Q of the (one) tuned circuit. So gain and selectivity increase at the same time.

I agree that the Q of the single tuned circuit is high. Then it has a bandwidth at its peak that is much too narrow and does not have steep slopes away from the peak which causes poor selectivity for the strong stations that interfere with each other and cover up the weak stations.

Many articles and Thesis's in Google say, "Low Cost. Selectivity and sensitivity are not good in a super-regenerative receiver as compared to other receivers".

In his article about super-regen receivers, Charles Kitchin of Analog Devices says, "The variable selectivity allows the operator to optimize the slope of the receiver's amplitude versus frequency characteristic (sounds like reducing the Q to me) to allow FM demodulation by slope detection".
He mentions "blocking" by strong local signals (I called it overload).
"The regen has great RF selectivity and gain. At the same time, both the gain and the selectivity can drop dramatically with very strong input signal" (which is what I said). https://www.arrl.org/files/file/Technology/tis/info/pdf/9811qex026.pdf

 

[godfreyl]

I think chucky was disagreeing with this statement from the OP:

...there is a trade-off between the sensitivity and selectivity among the super-regenerative receiver. I.e., if we increase the sensitivity, the selectivity would degrade.

 

[chuckey]

Audioguru , I agree that the super-regen suffers from all sorts of problem, mainly stability related (probabley curable with modern semi-conductors), but as I understand it gain and bandwidth are directly and inversely linked. As for bandwidth, I have heard of Qs in the order of 30,000 which at 1MHZ would give a bandwidth of 30 KHZ and a voltage gain changing microvolts into millvolts I think I'll rush away and build one!
Frank

 

[Audioguru]

As for bandwidth, I have heard of Qs in the order of 30,000 which at 1MHZ would give a bandwidth of 30 KHZ and a voltage gain changing microvolts into millvolts I think I'll rush away and build one!

Why do you want to make a horrible-sounding AM radio?

 

[listen]

Hi chuckey,

Pls. see the attached PDF file. Pls. see page2190 with yellow part.

it made me puzzled.

Thanks

I do not agree. The super-regen works by by increasing the Q of the (one) tuned circuit. So gain and selectivity increase at the same time. Can you supply any references for your statement?
Frank

 

[chuckey]

I do not really understand what the paper is saying, and can only defer to its very academic solutions. Its not at all intuative. :-(
Audioguru, Matron says its good therapy and might stop me from annoying the other patients.

Frank

 

[jiripolivka]

Dear friends, the super-regenerative receiver has been studied may years ago. The conclusions are:
1. Two kinds of SR receivers exist, one is self-quenched, the other has an external quench generator.
2. The SR receiver is typically an oscillator which oscillates with interruptions. To start oscillations, without any external signal it starts by noise, this is why a SR receiver generates a strong audio noise without a signal. A signal from antenna which is stronger than noise triggers the RF oscillation and is demodulated with a high gain.
3. SR receivers have a poor selectivity as the RF circuit Q is reduced by the quenching process. It is good as AM receiver, and tuned to the side of the bell-shaped resonant curve it can demodulate a FM signal. Due to typically 100 kHz FM spectrum bandwidth, Q is required to be low, still distortion occurs.
4. Now many SR receivers are used in low-cost UHF receivers, with a low Q they need no fine tuning. Many are noisy, so they can be used for short-range communication like door and garage openers.

Operating a SR receiver needs a skill, to tune the RF oscillator while adjusting the quenching circuit to optimize the output. Not too suitable for modern users used to "get data out" without any adjustments.