breadboard question...

[mstechca]

...so maybe my superregen has a colpitts in it.

I have it all on a breadboard, and when I calculated the frequency with the correct inductors, it was about 29Mhz than it should be. However, when I added 0.03uH (I assumed this number) to my 0.1uH, just because I think the breadboard adds inductance, I get closer to the correct value. In fact, I was only about 1Mhz away.

So just exactly, what is the inductance between any two connection points, provided they aren't connected to each other internally?

and my inductors have some wire exposed because I have them in a stand-up fashion, so I think there is some inductance there.

I don't make my own inductors. I use store-bought ones.

So what is the inductance per mm of the wire? It is about the same AWG of wire normal 1/4 watt resistors are attached to, and it is the same colour as well, and no windings on the wire.

I don't need approximations, but I need EXACT answers, because I am going to make a radio that changes stations upon the push of a button.

Later, I am going to get myself a whole bunch of 1pF capacitors so that I can build a chain of values and then be able to flip through many stations (well over 100). I already have a counter IC which I will use as well.

why capacitors over wire pieces for inductors? I think that the larger the capacitor in the LC circuit, the better the quality, because it is the inductor that makes a large amount of resistance.

 

[audioguru]

I have it all on a breadboard, and when I calculated the frequency with the correct inductors, it was about 29Mhz than it should be. However, when I added 0.03uH (I assumed this number) to my 0.1uH, just because I think the breadboard adds inductance, I get closer to the correct value. In fact, I was only about 1Mhz away.

If they aren't coupled, two inductors in series results in the total of their inductance. Inductors in parallel have a reduced total inductance.

So just exactly, what is the inductance between any two connection points, provided they aren't connected to each other internally?

A wire has inductance in series with it, the more its length then the more its inductance. Your breadboard has tracks with unknown thickness and your jumper wires also have inductance. I don't think you can accurately calculate the total inductance because on a breadboard it is all over the place.
Your problem is also having way too much capacitance between the tracks on the breadboard and between your jumper wires.

I don't need approximations, but I need EXACT answers, because I am going to make a radio that changes stations upon the push of a button.

Later, I am going to get myself a whole bunch of 1pF capacitors so that I can build a chain of values and then be able to flip through many stations (well over 100). I already have a counter IC which I will use as well.

You won't be able to calculate all the stray inductance and capacitance of a breadboard circuit.
You can't use a switch to change frequencies at VHF unless it controls the voltage of PIN diodes that do the switching. The capacitance between contacts of a switch and its wiring could easily be 30pF or more.
Do you know how little capacitance there is with only 1pF?
The loading effect and input capacitance of a counter will throw off the frequency of your oscillator way more and probably stop it.

why capacitors over wire pieces for inductors? I think that the larger the capacitor in the LC circuit, the better the quality, because it is the inductor that makes a large amount of resistance.

If you don't use the correct ratio of inductance and capacitance in a tuned circuit, then its bandwidth and Q will be way off.

 

[mstechca]

If they aren't coupled, two inductors in series results in the total of their inductance. Inductors in parallel have a reduced total inductance.

I knew that part. Resistors and Inductors are calculated the same way when connected in series/parallel.

Your problem is also having way too much capacitance between the tracks on the breadboard and between your jumper wires.

Here's the thing. It is far more expensive, and far more time-consuming to make PCB's for the superregen and always have to take out and place components in a PCB then it is to plug in and remove components on a PCB.

and because higher capacitance lowers the frequency, what is the capacitance between any two adjacent tracks on any breadboard?

You won't be able to calculate all the stray inductance and capacitance of a breadboard circuit.
You can't use a switch to change frequencies at VHF unless it controls the voltage of PIN diodes that do the switching. The capacitance between contacts of a switch and its wiring could easily be 30pF or more.
Do you know how little capacitance there is with only 1pF?
The loading effect and input capacitance of a counter will throw off the frequency of your oscillator way more and probably stop it.

The switch idea works for me. I am taking the tuned LC circuit connected to the emitter of the transistor, and instead of connecting the capacitor to ground, I am connecting it to an output of the counter, and this will create a ground or VCC for the capacitor depending on the counter result.

I am using 1pF capacitors because I want to be able to fine tune the stations without fiddling with a tuning capacitor. If the capacitors are too high, then fine tuning cannot be achieved without messing around with the inductor which I do not want to do.

 

[zachtheterrible]

mstecha, you CANNOT use a breadboard for anything thats even remotely high frequency!

Why not use veroboard? you know, the stuff with a bunch of holes in it.

 

[mstechca]

I want to insert and remove pieces quickly.

If there is capacitance between two adjacent connection strips on a breadboard, then I'm sure there is capacitance between two adjacent strips on a circuit board (or a veroboard).

and if the strips of the veroboard go on forever, doesn't the capacitance go up, and up? and I say that because if we assume 1pF capacitance between any two points, and I go down the line, I could do 1pF + 1pF + 1pF... and so on.

 

[audioguru]

what is the capacitance between any two adjacent tracks on any breadboard?

Their manufacturers don't reveal it in their specs and I haven't measured it. Measure yours.
I would guess that tracks with a 0.1" spacing and 6" long would have up to 47pF between them. A pcb or Veroboard would have about 2pF.

 

[audioguru]

The strips on a Veroboard are cut with a drill bit to a short length.

 

[Nigel Goodwin]

The strips on a Veroboard are cut with a drill bit to a short length.

I used a drill for many years, but it's FAR easier to use the correct 'spotface cutter' tool which the board manufacturers sell. They are only cheap, and well worth having.

 

[audioguru]

I use my drill press to cut pre-marked tracks. Then I can cut 30 and sometimes 60 in only a minute. :lol:

 

[Optikon]

I use my drill press to cut pre-marked tracks. Then I can cut 30 and sometimes 60 in only a minute. :lol:

I use a small battery powered dremel tool. It can route out tracks as fast as you can draw them. The OP mentioned the other types of boards are too expensive and time consuming. I wonder if he realizes that a piece of copper PCB is the least expensive and as for time consuming, how much time has he spent troubleshooting and pondering why his high frequency circuit isnt working right on a low frequency prototyping method.

And now considerations of measuring parasitics on that thing so he can tune! gastly! the design sounds doomed from the outset.

 

[Nigel Goodwin]

And now considerations of measuring parasitics on that thing so he can tune! gastly! the design sounds doomed from the outset.

A little knowledge is a dangerous thing! :lol: