My 1 transistor FM Super-Regen Receiver!

[betwixt]

Just a word of caution:

Be careful using these receivers in areas where they might cause interference to other users. The nature of super-regenerative receivers dictates they must transmit a certain amount of interference and it will not be a 'clean' signal, it could spread quite widely into nearby frequencies. Adding the pre-amplifier stage will not only make the receiver more sensitive, it will block some of the interference and also reduce the effects that nearby objects have on altering the tuning. I would go with the pre-amp if at all possible.

As pointed out earlier these are AM receivers not FM but they will convert frequencies shifting in and out of their passband into variable amplitudes (slope demodulation) so FM can be resolved. I have built super-regen receivers working up to almost 1GHz with success so higher frequencies than the FM broadcast band are certainly possible.

If being used near an airport or emergency services PLEASE heed the warning about the interference they can cause. Although you might be able to hear the radio traffic, you could be blocking it for essential personnel.

Brian.

 

[vfone]

When you start doing your first ever receiver, you have to forget about any generated interferers, otherwise you loose the entire fun.
Sometimes, even if you are an experienced professional, is fun to think and do hobby projects like a beginner...
Most of the PhD’s in RF engineering never built in their life, a simple one or two transistor radio.

 

[sanjubluerock3]

Hiii transistor495. can you please send me the pcb design for this fm receiver

 

[zlatkoMM]

Look into upper posts there is pcb.gif ....

 

[edsonstedile]

Re: one transistor fm radio

Friends,
I've successfully made Patrick Cambre's single transistor regenerative FM Radio using BF245C in place of MPF102 suggested. I didn't have any trouble except my BF256 didn't work on first turn ON! Just replaced and it works very fine. I've used a 2K regen pot in place of 1K suggested, but its funny that my later experiments with 1K and 5K didn't work at all!!

It may be due to the transistor variations.

I recommend you to build this little wizard. It was really an amazing experience that it picked up stations without any antenna initially. The audio was 90% clear and contains bass treble frequencies made me shocked.

It is a very sensitive and selective regen receiver. Try it!

I WOULD APPRECIATE IF YOU SEND ME THE SCHEMATICS OF THIS RECEIVER.
I DID NOT FIND IT ELSEWHERE.
THANKS IN ADVANCE.
EDSON STEDILE - edsonstedile@gmail.com

 

[Audioguru]

Re: one transistor fm radio

I WOULD APPRECIATE IF YOU SEND ME THE SCHEMATICS OF THIS RECEIVER.
I DID NOT FIND IT ELSEWHERE.

In Google, I entered Radio Shack Special and found links to it and a correction to it. But the website of Patrick Cambre does not work today.
Then I entered into Google "Patrick Cambre FM Radio Project" and got many more links to his project.

 

[ALERTLINKS]

**broken link removed**

 

[zlatkoMM]

And another one ..very simple design and work fine
look into image...

 

[Audioguru]

And another one ..very simple design and work fine
look into image...

Your schematic is too small and is a negative. Can you make it larger, clearer and with a white background please?

 

[zlatkoMM]

I cannot crete this image for some unknown reason..?
This image is created in program called IC.
**broken link removed**

 

[alexan_e]

Here is the BW version with white background

 

[Audioguru]

Alex, thanks for producing a normal-looking schematic. I lost my image viewer with a "negative" button when I got Win7.

This schematic is missing a dot at the emitter and is missing another dot at the collector of the RF transistor.
It appears to be a simple regenerative AM radio (a Colpitts oscillator) with the pot adjusting its sensitivity. It is not a super-regen that automatically adjusts its own sensitivity. It can receive distorted FM using slope detection if it is tuned to one side of a station.

 

[zlatkoMM]

Detection isn't done by slope detection, but by synchronising the oscillator frequency to the frequency swing of the incoming FM RF signal. The oscilator frequency follows the frequency swing of the incoming RF signal, the result is that the LF signal is detected by curent changes of the oscilator stage
I have built an FM regenerative receiver with an RF preamp stage, oscillator with the same topology like the noisy regen. The oscillator is synchronised to the incoming signal. Detection is done by slope detection. The results are much better than with an FM regenerative receiver without any RF preamp stage.

Schematic:
https://www.uploadarchief.net/files/download/fm-synchroontuner(1).gif

 

[Audioguru]

The frequency of your oscillator does not syncronise with the incoming FM, because if it did then its current would not change and it would not detect the FM. Instead its frequency is fixed and your circuit detects AM (slope detection for FM) plus all the clicks and pops heard on an AM radio.

A real FM radio has AGC on its RF amplifier and it is tuned to avoid overloading caused by strong local stations.
A real FM radio has limiters in its IF amplifier to avoid detecting AM.

 

[zlatkoMM]

Oh my g ...you again
with your anti-regen attitude and useless explanation.
If you don't have nothing to say or you don't like experiments please post
somewhere else where maybe someone need your junk explanation.
Oh i forget maybe you are baned from all others electronic forums.

- - - Updated - - -

Another well designed VHF FM radio with FET you can see on shematic:
http://aurelsoft.ucoz.com/VHFFM.png

 

[betwixt]

I have to side with Audioguru on the way this functions. It IS posible to lock the oscillator to the incoming signal if there is a control method for doings so (PLL style), but there is none. Furthermore the change in oscillator current due to a small frequency shift compared to the 100MHz or so it's designed to work at would only recover an incredibly tiny audio signal, especially when developed across only 10K of resistance. Granted, there will be a degree of injection locking as there is in most self-quenching super-regenerative receivers but that would tend to reduce the audio even further. It is an AM receiver and the audio recovered from it is from slope demodulation.

The FET design in post #35 is better in most respects but is still AM.

I'm not critisizing the quality of slope detectors or super-regens, but to it's wrong to confuse the way the designs shown here work. They can receive FM signals of course but they work equally well, if not better, when receiving AM and they do not take full advantage of the properties of true FM receivers.

Brian.

 

[Audioguru]

Another well designed VHF FM radio with FET you can see on shematic:
https://aurelsoft.ucoz.com/VHFFM.png

It is another old AM regen radio that slope-detects the FM broadcast band.
Hee, hee. It uses an old 2N2369 transistor as its RF amplifier. I still have some that I got about 45 years ago.

There are a few good articles about super-regen radios on the internet.
Here is a good super-regen radio project with an excellent description. It explains how a "super-regen" automatically adjusts the gain of an ordinary regen radio:

 

[zlatkoMM]

Somewhere from net :

Slope detector
The slope detection is a method of FM-demodulation which converts the received FM signal to AM and demodulates with an envelope detector.

Balanced slope detector is frequency diskriminator which is FM demodulator,right?

 

[Audioguru]

A good FM radio has an IF bandwidth about 220kHz wide with a flat top and steep sides (a regen or super-regen radio does not). Then balanced slope detection is impossible. A frequency discriminator, ratio detector, or digital pulse counting can detect FM.

Look at FM detectors in Google. Here is an article: **broken link removed**

 

[betwixt]

Somewhere from net :

Slope detector
The slope detection is a method of FM-demodulation which converts the received FM signal to AM and demodulates with an envelope detector.

Balanced slope detector is frequency diskriminator which is FM demodulator,right?

It's not a true FM demodulator although it can recover some audio. In a real FM demodulator, the carrier frequency equates to the 'zero' of the recovered audio and shifting the frequency above or below center results in an increase or decrease in the voltage output from the demodulator. This means you can filter the carrier to limit it's bandwidth and the optimum tuning point is central to the carrier where the signal is strongest. In a slope detector, tuning to the carrier may result in little or no audio at all. It relies on the tuning point being half way down the edge of the bandwidth slope so the center point is only half signal level. As the signal moves closer or further away from the tuning point it amplitude seems larger or smaller and this is what is recovered as AM. There are many problems with slope detection, poor interference rejection, poor selectivity, poor adjacent channel rejection, they are less sensitive because you are tuned to the signal fringe and their linearity depends on the passband shape.

To complicate matters, the principle of super-regeneration is that you pre-empt the start of oscillation by 'kicking' it with the incoming signal. The quench oscillation is usually just above hearing range and it's the amplitude of the 'kick' to each of the quench cycles that causes the current to change and hence recover the modulation. Beacause of this, they tend to have a signal threshold below which they do not work and that causes non-linearity as the incoming signal moves further from the tuning point.

Brian.