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Regenerative receiver does not work, why?

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neazoi

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Hi I have built a regenerative receiver using this schematic https://ok1ike.c-a-v.com/soubory/tipy/001.gif
But it does not work.
If I connect a 10K from the base of the transistor (c3 pin) to the vcc, then I can listen to stations but the controls do not change neither the frequency or the regeneration. I can listen to all band stations at once, no selectivity.

Any ideas of what might be wrong, before I abandon the circuit and consider it as junk?
I like the fact that it uses pots instead of caps for the tuning and that it does not use tapped coils.
 

jiripolivka

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The secret is in the oscillator stage, it should oscillate and be tuned. Check the voltages on potentiometers.
Use correct capacitor and coil values for each selected band.

- - - Updated - - -

Did you connect the varicap correctly? Check its voltage when tuned by the pot.
 
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neazoi

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The secret is in the oscillator stage, it should oscillate and be tuned. Check the voltages on potentiometers.
Use correct capacitor and coil values for each selected band.

- - - Updated - - -

Did you connect the varicap correctly? Check its voltage when tuned by the pot.

I have used the components for the 50-30 meter band only currently.
The varicap is in correct orientation, else it would get very hot. Also the tuning voltage in the varicap pin is varied from 0v to a bit less than 9v, which indicates correct operation at that point.
I have tried to tap the oscilloscope in different point of the oscillator and made different settings on the regen pot, so that I can see the oscillations on the scope, but it is not happening.
As a last resort I connected a 10k resistor from the base of the oscillator transistor to the vcc and now signals can be detected but no tuning or selectivity at all. Without this resistor how can the transistor be switched on anyway?
 

betwixt

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I can't see that ever working reliably.
I presume it is supposed to work as a zero IF receiver with detection using the B-E junction of the top BF199. It would rely on the oscillations starting before it could bias the transistor to start the oscillations - not a stable condition! The capacitor values also look suspicious as well, I would imagine the tuning range would be very limited as the varicap is swamped by larger fixed values. Basically, it's an incorectly biased oscillator with a poorly designed wideband antenna amplifier connected to it.

Brian.
 

neazoi

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I can't see that ever working reliably.
I presume it is supposed to work as a zero IF receiver with detection using the B-E junction of the top BF199. It would rely on the oscillations starting before it could bias the transistor to start the oscillations - not a stable condition! The capacitor values also look suspicious as well, I would imagine the tuning range would be very limited as the varicap is swamped by larger fixed values. Basically, it's an incorectly biased oscillator with a poorly designed wideband antenna amplifier connected to it.

Brian.

Sometimes you have to ask before build...
Thanks Brian

- - - Updated - - -

Sometimes you have to ask before build...
Thanks Brian

How would you review this circuit?
http://circuitsalad.com/2014/12/06/another-excellent-performing-regen-circuit-coming-shortly/
It seems to have good characteristics and tested.
I do not think multiband operation would be difficult, since it uses no tap coil.

Is the antenna really isolated from the tank circuit so that no oscillations escape to the antenna, I don't think so?
 

betwixt

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I don't think so either.
Up to the point of oscillation, the first transistor works as a common base amplifier which is good. If it does oscillate, the antenna is connected directly to the oscillating stage so it will radiate interference.

What puzzles me in the design is the tuned circuit. In the configuration shown it has lowest imedance at signal frequency when you normally want it to be highest impedance at that time. I'm suspicious that it doesn't work as intended and the 'receiving' is actually done by the Q multiplier, not Q3 and Q4.

Brian.
 

Audioguru

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A regenerative receiver is used in a child's cheap toy car. Make a real radio instead.
The schematic uses BF199 NPN transistors but wrongly shows them as PNP. I wonder what else is wrong with the circuit?
 

I14R10

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A regenerative receiver is used in a child's cheap toy car. Make a real radio instead.
The schematic uses BF199 NPN transistors but wrongly shows them as PNP. I wonder what else is wrong with the circuit?

I agree. I made one myself as my first radio. It's based on C. Kitchin design. I could actually hear some radio stations from distance of a few thousand km. But they all were radio stations (I was in a wrong band) and I could not hear any SSB signals.
 

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Regenerative receivers have a lot going for them. No images, good overload performance, good selectivity and they work with AM, DSB and SSB. They can also receive FM subject to the normal lmitations of slope detection but consider that in a regenerative receiver you can adjust the slope! Their only real disadvantage is the difficulty of tracking the regeneration and maybe pre-amplifier tuned circuits.

The particular design shown has lots of limitations and like most designs on the internet, is based on trial and error using bits fom a junk box instead of using good theory and selected parts.

I have in mind a new approach, call it "Betwixtodyne" which works in theory but to my knowledge has never been built. It allows continuous tuning with tracking of the regeneration point. It makes the regeneration control a bandwidth control instead with the option to go 'negative bandwidth' to resolve DSB and SSB. I will get around to trying it one day but for now it just bounces around in my head. I suppose that's because there's lots of empty space there. :grin:

Brian.
 
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neazoi

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Regenerative receivers have a lot going for them. No images, good overload performance, good selectivity and they work with AM, DSB and SSB. They can also receive FM subject to the normal lmitations of slope detection but consider that in a regenerative receiver you can adjust the slope! Their only real disadvantage is the difficulty of tracking the regeneration and maybe pre-amplifier tuned circuits.
Image rejection? I do not think so. The image in a regen is the opposite sideband, like a common DCR. The selectivity of the Q-multiplier is not so good to reject the opposite sideband.
Good overload performance? I do not think so either. If you try to inject a low power signal close to a high powered signal the regen stage may lock to the high power signal instead if receiving the low powered signal.
I tend to think of regens more like very simple radios that should work very well but only considering as a measure the low amount of components you put in.
The particular design shown has lots of limitations and like most designs on the internet, is based on trial and error using bits fom a junk box instead of using good theory and selected parts.
I wonder if a good regen design exists somewhere. Kitchin's design https://www.google.gr/url?sa=t&rct=...MCFap8NU2lsBCxpC7x1LWRQ&bvm=bv.95039771,d.d24 seems good but is it really? Also the multi-tapped coil is scary. My thought is for a tap-free coil, this would be great!
I have in mind a new approach, call it "Betwixtodyne" which works in theory but to my knowledge has never been built. It allows continuous tuning with tracking of the regeneration point. It makes the regeneration control a bandwidth control instead with the option to go 'negative bandwidth' to resolve DSB and SSB. I will get around to trying it one day but for now it just bounces around in my head. I suppose that's because there's lots of empty space there. :grin:
Brian.
That is what I have also thought, a microcontroller that controlls both frequency and the feedback loop. But the micro has to be a "learning device" since these curves difference is not always the same and they are not linear.

This "learning device is what I have thought it would be useful in many projects. For example you move a stepper motor with your hand to the position wou want. The mico, learns from that movement and next time it performs it automatically. It is more like a record-play action.
 

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By image rejection I meant from the local oscillator mixing products, obviously without an LO they can't exist. For AM the sidebands are identical so the image isn't a problem. The locking problem can only exist if the stage is actually in oscillation, up to the brink of oscillation it shouldn't happen but I agree that all receivers will eventually overload in the presence of a strong signal.

The 'Betwixtodyne' principle doesn't involve learning and with care it may be possible to design without a microcontroller although it would certainly be easier with one. The idea is to use a negative reistance device as the amplifier because it gives relatively smooth control of the gain up to and beyond oscillation using only a voltage. The optimum voltage is found by periodically (tens of times a second maybe) taking the circuit beyond oscillation point by increasing the voltage and monitoring the large voltage increase at the detector. The voltage is then reduced by the desired amount to 'back off' the oscillation point or leave it alone for SSB/CW reception. If the process can be done quickly enough, the deliberate oscillation products can be filtered out and the audio left for amplification. Because the circuit dynamically finds the oscillation point, the regeneration control becomes a 'how much to back it off" control instead and shouldn't change significantly at different receiver frequencies. In respect of oscillation it works rather like the quench signal in a super-regenerative receiver. You know it's there but you never hear it.

Brian.
 

chuckey

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In your circuit you have a RF amp connected to the aerial. The feed from it then goes to the regenerative detector. Disconnect C5 and the detector now becomes an oscillator at its tuned frequency depending on the setting of the 10K feeding the 3k3 collector load. So set the tuning pot to one extreme and the mentioned pot (reaction control) also, measure the DC voltage on the collector. If the transistor is oscillating, then grasping the tuning inductor (L1) will stop it oscillating, the collector current will change and your measured voltage will change also. Try this out across the tuning range and settings of the reaction control. You should get a feeling of whether this stage is working. it will certainly stop oscillating when the reaction control is set to zero volts, but then you will have zero volts to measure.
Once you are certain that it will oscillate above some voltage on the collector, then reconnect your C5 so the problem will now be to figure out what frequency the receiver is tuned to. And you know what voltage not to exceed if you want it to be a receiver, else it will be a transmitter!
Frank
 
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