Superregen (a partial solution?)

[Nigel Goodwin]

I wonder if the breadboard is causing difficulties, because I'm doing alot of my testing on a breadboard.

How many times have you been told you can't use a breadboard at VHF?, do you never listen to anything you're told?.

 

[audioguru]

He is agreeing with me.
I think it is just two components (resistor and capacitor), and you are saying it is the capacitor and inductor.

My resistor capacitor and inductor are connected together the same way. except the other end of the inductor is connected to collector and the resistor and capacitor are pull-ups instead.

The tuned high impedance tank is supposed to be at the transistor's high impedance collector. The quenching parts are supposed to be at the transistor's emitter to "quench" or cutoff the transistor when its signal gets high.
Your circuit is backwards: the high impedance tank is at the transistor's low impedance emitter and the quenching parts are at the collector which will not cause the transistor to cutoff.

When the emitter inductor is at 0.1uH I hear more "hum". When I replaced it with a 1uH inductor, I hear more stations.

The emitter inductor is supposed to be a high impedance choke, not a tuned tank. The high value of 1uH makes a pretty good choke.
Maybe the hum that is heard is TV vertical sync which is 4.5MHz away from the sound carrier and is AM modulated. Your circuit has only a single tuned circuit so its selectivity is pretty low. Real radios have many tuned circuits for good selectivity. Your circuit detects AM, real FM radios don't.
Put the tank at the collector where it belongs and put the quenching parts at the emitter where they belong.

I wonder if the breadboard is causing difficulties, because I'm doing a lot of my testing on a breadboard.

When are you going to learn that high frequency radio circuits don't work on a breadboard due to its very high stray capacitance and inductance.
Use a pcb or Veroboard with very short traces.

 

[mstechca]

Your circuit has only a single tuned circuit so its selectivity is pretty low.

Single-tuning is intentional. I want to add a poor-mans varactor arrangement to it later.

Real radios have many tuned circuits for good selectivity.

Which then requires more mathematical equations.

Your circuit detects AM

That's ok, as long as it can detect ANYTHING in the VHF/UHF range, I'm happy.

Put the tank at the collector where it belongs and put the quenching parts at the emitter where they belong.

You must be one of those guys that stick with the books. :LOL:

When are you going to learn that high frequency radio circuits don't work on a breadboard due to its very high stray capacitance and inductance.

Audioguru, It's called giving myself unlimited chances at perfecting the same circuit without wasting time or money on more board.

I understand what you are saying. I don't know the maximum frequency I can work with before going to a PCB. I can pick up FM stations without going to a PCB.

A huge advantage with using a breadboard is that I can test 100's or even 1000's of circuits on the same breadboard before it is toast. On a PCB, I'll be lucky if I can test a few variants of the SAME circuit (namely replacing parts with different part #'s).

 

[Nigel Goodwin]

You must be one of those guys that stick with the books. :LOL:

He's one of those guys who builds things that work!, not sticking to the rules is OK if you know what you're doing (and why), your things don't work because you don't know what you're doing, and don't have a clue why

A huge advantage with using a breadboard is that I can test 100's or even 1000's of circuits on the same breadboard before it is toast. On a PCB, I'll be lucky if I can test a few variants of the SAME circuit (namely replacing parts with different part #'s).

Except you CAN'T build VHF circuits on a breadboard, it's yet another reason they don't work - OK for audio use, but RF no way, and VHF RF?, not a hope in hell!. You keep asking for equations?, are you adding the breadboard capacitance into these equations?.

 

[audioguru]

Except you CAN'T build VHF circuits on a breadboard, it's yet another reason they don't work.

Sometimes he says it works.
I think it is just a crystal radio. A tuned LC and a transistor's junction as an AM detector diode.
I wonder if it works better without a power supply.

 

[zevon8]

Sometimes he says it works.
I think it is just a crystal radio. A tuned LC and a transistor's junction as an AM detector diode.
I wonder if it works better without a power supply.

Pickard found by accident that his set worked better without the batteries. He thought his crystal reciever was neat enough to patent.... a hundred years ago...

I think Audioguru is right, this has "degraded" to being a foxhole radio, sans the razor blade.

 

[mstechca]

crystal radio, LMAO.

I have determined that the wrong combination of the resistor and capacitor in the quench is causing problems, as well as a bad NPN transistor.

It's not a crystal radio.

 

[audioguru]

For an oscillator to quench, it needs to be cutoff. A parallel resistor and capacitor in series with the emitter to ground will charge and cutoff the transistor. Your circuit doesn't have a parallel resistor and capacitor in series with the emitter to ground.

 

[audioguru]

MStechca,
Here is an article about "How to design a super-regenerative receiver".
**broken link removed**
It has the normal circuit of an oscillator with the tank at the collector and the quenching parts at the emitter.
It has the normal supply bypass capacitor that your circuits never have.
IT HAS FORMULAS and MATHEMATICAL EQUATIONS for you to guess about how much is your stray capacitance and inductance.

 

[Nigel Goodwin]

MStechca,
Here is an article about "How to design a super-regenerative receiver".
**broken link removed**
It has the normal circuit of an oscillator with the tank at the collector and the quenching parts at the emitter.
It has the normal supply bypass capacitor that your circuits never have.
IT HAS FORMULAS and MATHEMATICAL EQUATIONS for you to guess about how much is your stray capacitance and inductance.

Do you think he could understand the formulas given there

A nice article, but somewhat technical for someone who builds by random chance

 

[mstechca]

"tap tap" again Bryan1 :LOL:

Before I saw this reply, I actually managed to pick up a faint TV station. it sounded like CTV (from Toronto). and that is all from just playing with the capacitor (connected across the 18K pull-up resistor).

I noticed that if I make the capacitor too large, I get a metronome style sound. So I know I'm on the right track so far.

I still can't seem to determine the optimum quench frequency. I'll look again at that page you pointed out to see if it is there.

I'm beginning to think that my room is 1/2 the problem because I take a store-bought radio and try to connect to a distant station (103.5Mhz) with a long antenna, and with a short one, and I can hardly pick it up. It is only located in toronto. The stations that I can pick up are 102.9Mhz in Hamilton which takes up at least 1/8th of the band, and I can pick up 104.5Mhz in Toronto.

But it seems that if I have the antenna end in the right spot (somewhere at a corner on my ceiling), I can pick up 103.5Mhz a bit more.

If I drilled a hole in my ceiling until I can see the sky and stick the antenna through that, would I be able to pick up stations better? LOL

By the way, I live across the street from a chain of hydro (electricity) towers.

 

[zevon8]

Just as an aside, you can't randomly choose antenna lengths either, over-simplified, you may pick a length that is a short circuit at the desired frequency.

 

[audioguru]

MStechca,
I'm not far from you and my home stereo FM tuner with rabbit ears for its antenna and my car radio with its whip antenna pick up an FM radio station on just about every frequency (200kHz apart) from 88MHz to 108MHz. That is about 90 to 100 stations.
My 20 dollars Sony Walkman FM stereo portable radio picks up about 40 or 50 FM stations with its earphones cord as its antenna.

The crappy radio that I got for free and is sold for $1.00 at the dollar store picks up 4 or 5 FM stations, all across its overloaded dial.

 

[mstechca]

The fact is that I am more interested in higher frequencies than the FM band. I might be able to make a decent FM radio with my setup.

It looks like I'll have to generate my own equation.

So far, one equation that is close to working is: carrier frequency / Hfe = Quenching frequency.

 

[audioguru]

It looks like I'll have to generate my own equation.

So far, one equation that is close to working is: carrier frequency / Hfe = Quenching frequency.

Nope.
1) The transistor's Hfe (Hfe is its AC gain, hFE is its DC gain) must be more than 1 at the RF frequency so that it can oscillate.
2) The quenching frequency must be at least 2 times higher than the highest modulation frequency to avoid beats. Make the quenching frequency at least 4 times higher than the highest modulation frequency so you can use a reasonable lowpass filter to remove the quenching frequency from the output.

The Hfe of the transistor has nothing to do with the quenching. The RC network in series with the emitter to ground determines the quenching frequency.

First you must move its tank to the collector and move its quenching parts to its emitter where they belong. Then you can add a positive feedback capacitor from collector to emitter and you will have a super-regen receiver.
Don't forget to add supply bypass capacitors, about 1nF ceramic for RF and 10uF or more electrolytic for audio.

 

[mstechca]

2) The quenching frequency must be at least 2 times higher than the highest modulation frequency to avoid beats. Make the quenching frequency at least 4 times higher than the highest modulation frequency so you can use a reasonable lowpass filter to remove the quenching frequency from the output.

I'm still unclear with "modulation frequency". Is it the oscillator frequency?

 

[audioguru]

I'm still unclear with "modulation frequency". Is it the oscillator frequency?

Modulation is the information in the transmission. If it is ordinary audio then it could extend up to 20kHz which is as high a frequency as you can hear. If it is a stereo FM or TV broadcast then it has mono audio from 50Hz to 15kHz, a 19kHz stereo pilot signal and 23kHz to 53kHz stereo subcarrier sidebands. It might even have data modulated up to 100kHz.

To receive your local TV audio without interference from the quenching oscillator beating with the stereo pilot or subcarrier sidebands then the quenching oscillator must operate at 106kHZ or higher.

 

[mstechca]

I knew that the maximum frequency humans can hear is 20Khz, but how did you know the other information? I can't seem to find it anywhere on the net.

and are there any other modulation frequencies of interest out there?

 

[audioguru]

how did you know the other information? I can't seem to find it anywhere on the net.

I learned about FM stereo when it was first broadcast and I built a kit FM stereo multiplex adapter to go with my kit FM tuner. Its detailed operation is in Google, search for FM Stereo.

are there any other modulation frequencies of interest out there?

FM stations used to broadcast SCA "restaurant" music around 67kHz. Now they have data that says their type of music.
Some TV stations have a second language and data modulated at ultrasonic frequencies.