fixing current

[mstechca]

My superregen is nearing completion, but I have found something interesting.

All detectors have a pull-up or pull-down resistor of some sorts (to deliver power to the entire detector). In transistor FM transmitters, I think the supply resistor is connected between emitter and ground. It is "this" resistor that changes the result of the entire receiver.

Here is what I have done:

I tried 6VDC of power, and used a 27K resistor. I get alot of noise, and maybe one or two stations if I am lucky.

I changed the power source to 3VDC and I get a station in nice and clear with no distortion at all. In fact, this station is about 60 km away from me.

I changed the voltage to 6VDC and changed the resistor to 47K. The station remains clear.

This makes me think that there is a limit to the current an FM detector can deal with.

Because I want good quality like I had, I want to be able to use a battery and have the receiver run until the battery drops under 3V.

Since the resistor has a big impact on my reception quality, is there a circuit out there that automatically selects the right current to output to the detector, based on input voltage?

Oh by the way, when I tried 47K resistor with 3VDC, I got absolutely nothing.

 

[Nigel Goodwin]

It gets worse! :roll:

 

[ThermalRunaway]

Don't forget to make sure all your components are suitably topped up with pressurised smoke, otherwise your modified receiver wont work for very long.

Brian :roll:

 

[evandude]

you could make a transistor current source, then the current will be the same regardless of input voltage (within a certain range, at least), unlike using a resistor.

I don't know anything about superregens though, so someone else will have to tell you if a current source is a good thing to put in there.

 

[ThermalRunaway]

I think the point to be made here is that he doesn't know what's good or not good to put in there either. And that's something you should probably be clear on when you make the decision to build one. It's fair comment that he's wanting to experiment with the receiver by trying different components and ideas, but if you're going to that I think it's even more important that you understand what you're doing before you build it.

Brian

 

[mstechca]

you could make a transistor current source, then the current will be the same regardless of input voltage (within a certain range, at least), unlike using a resistor.

I don't know anything about superregens though, so someone else will have to tell you if a current source is a good thing to put in there.

In my superregen, it is required to keep a cheapie battery from making my reception a mess.

how did I figure this?

Because 27K is almost half of 47K., and using 27K at 3V gives the same results as using 47K at 6V. So if we work out ohms law here, the current is about the same. :wink:

I must be the only one here that actually deals with superregens. :lol:

 

[mstechca]

you could make a transistor current source, then the current will be the same regardless of input voltage (within a certain range, at least), unlike using a resistor.

I forgot to ask, where can I find a schematic for this?

 

[evandude]

knowing that a different current will affect the operation, which you seem to have found out only by experimentation, is not the same as understanding WHY and HOW it affects it, which is what he was talking about.

if you want a circuit, google for "transistor current mirror", you'll find tons.

 

[audioguru]

Since it works OK with a 27k resistor and 3V, then why not use a 3V low-dropout voltage regulator IC for it? Then you can use just about any battery until it is nearly dead.
I know, you can't afford the dollar for the IC. :cry:

Its biasing is obviously being changed by the change of battery voltage.

Your super-regen "radio" must be very senstive to pickup a 500,000W radio station a whopping 60km down the road. :roll:

How far does it transmit interference? :?:

 

[mstechca]

Since it works OK with a 27k resistor and 3V, then why not use a 3V low-dropout voltage regulator IC for it? Then you can use just about any battery until it is nearly dead.

I'm thinking any voltage regulator will do myself, but some manuals say I should have capacitors between +ve and -ve at both the source voltage (3 - 9V), and the destination voltage (3V). I'm afraid the capacitors will give too much bandwidth.

I know, you can't afford the dollar for the IC.

I can get the dollars, but my space is tight. I would like to see myself making circuits with parts crammed together I just can't afford the dollars for the large project boxes.

Its biasing is obviously being changed by the change of battery voltage.

The entire circuit is affected by the battery.

Your super-regen "radio" must be very senstive to pickup a 500,000W radio station a whopping 60km down the road. :roll:

You can say that. PLUS, I'm not even using an antenna.

How far does it transmit interference? :?:

My radio doesn't transmit interference during my tests. The only time it did was when I was trying to receive the same station as another radio, and then my radio transmitted interference to that radio. It never transmitted interference to the TV :wink:

 

[audioguru]

Since it works OK with a 27k resistor and 3V, then why not use a 3V low-dropout voltage regulator IC for it? Then you can use just about any battery until it is nearly dead.

I'm thinking any voltage regulator will do myself, but some manuals say I should have capacitors between +ve and -ve at both the source voltage (3 - 9V), and the destination voltage (3V). I'm afraid the capacitors will give too much bandwidth.

It is recommended to have a small input bypass capacitor and an output one to improve the transient response of voltage regulator ICs. The capacitors are a dead short to audio and RF frequencies so how can they possibly affect bandwidth?

 

[zachtheterrible]

I know everyone can't stand listening to mstecha go on and on about his superregen, but if I might say something in his defence: WHO CARES!?! :lol: If that's what he wants to spend his time on and he enjoys it let him be. This is his way of figuring out how radio and electronics work, there's nothing better than hands-on experience.

No offense to anyone, I just feel kind of bad that mstecha has to take a bunch of complaining everytime he posts on his superregen circuit.

 

[ThermalRunaway]

Point taken.