Tuesday, December 10, 2019

Lambda Diode Oscillator

This simple oscillator will drive a converter to feed DBM or Gilbert Cell. The first step in building a new radio will be the LDO. It can be made with plug in coils and be multi band. It can hardly get any simpler. A couple of JFETs and a resistor feeding a tank circuit will work. A series resistor to limit the current is a good idea.

The resistor is being changed to determine what size pot will work.
The plan is to put a 470 Ohm resistor in series with a 1K Ohm pot.
A low value resistor allows the current to soar and a high value will kill the oscillator.  The 470 Ohm to 1470 Ohm should be a good trade off.

Thursday, December 5, 2019

relating a sine wave amplitude to the phase angle

Rotating the phasor creates a sine wave. The amplitude of the phasor is the sine of the angle (Assuming a max amplitude of 1). If the max was 100 the phasor would be 100* sine(theta) etc.

The angular velocity can be measured in degrees and using a sine table the amplitude can be determined. As an example let's look at 45 degrees. Sine is the first column. sine 45 degrees is .7071. Assuming a 100 volt peak the amplitude at 45 degrees would be 100*.7071 = 70.71.

Using the sine chart it would be possible to determine the value of the signal at any angle or conversely to determine the angle at and signal level. Now you can assign values to the waveform and determine the angle using the chart.

Wednesday, December 4, 2019

A mind experiment into the world of Electro - Magnetics. Part 6

In this series of screen shots I show a transmission line with different feed Z and load Z.

What effect does matching the load Z to the feed line Z have?

What effect does lowering the generator Z have?

Consider R1 as an antenna, when the signal is radiated (absorbed by the load) we see no reflected signal and the generator can handle more power. The rule of thumb often quoted is for maximum power transfer we need to match the load to the generator. This is true BUT the generator drops half the power.
 Food for thought.

A mind experiment into the world of Electro - Magnetics. Part 5

As a field expands and contracts it will effect its surrounding. An inductor has self inductance when the fields from one turn interact with the other turns in the coil. Ifd the field is captured by its neighbors it will release its energy. In the coil energy is absorbed and released back into the circuit.

In an antenna the energy escapes into space and is radiated.

The field would build and collapse. The energy is contained.

If the energy breaks away it is radiated.

Now consider an AC current flowing in a conductor. What determines if it is radiated or not? 

A mind experiment into the world of Electro - Magnetics. Part 3

Consider the domino effect. What if we could wave a magic wand and knock them down then wave it the other direction and stand them back up. Perhaps a double ended wand wave one end and they fall wave the other and they stand again.
Maxwell's law states an electric field in motion creates a magnetic field. In the mind experiment the wand would be an electric field and the dominoes the magnetic field.
As an electrical potential is placed on a conductor it will create a magnetic "B" field around the conductor. An AC field will produce a B field in one polarity as it goes positive and a B field in the opposite polarity as it goes negative. The fields and motion are at 90 degrees to each other.

So our dominoes would stand - fall - stand in opposite direction.
This is enough for now. More later.......

Thursday, November 28, 2019

A mind experiment into the world of Electro - Magnetics. Part 2

A wire with no current flow will have its charges in random directions.
They could be in the four compass points and an infinite number of other directions.
The electron spin producing the fields.
Charges in motion create field in all directions. Now we send a charge down the wire and it creates a unifying effect.
We can determine the direction using the right hand rule. A wave can travel at near the speed of light BUT the electrons are basically stationary. The electrons orient with respect to the wave and the magnetic field is strengthened (it is already there just in random orientation.). More later.....

A mind experiment into the world of Electro - Magnetics. Part 1

Einstein would use real world examples to study the invisible world. I am not the genius he was but I will attempt a simple analogy. First the item I selected to demonstrate the principle is a level gauge. The sight gauge is made of a series of magnetic rollers.
Here we have a datasheet for one.
The flappers are white on one side and red on the other. As the level increases a magnet on a float causes the roller to flip over.
In this system we see two possible positions.
In the invisible world we can have an infinite number of positions. If the red is the north pole we can determine the position using the right hand rule.
Point your finger in the direction of the motion (spin) and the thumb points to the north pole. So if we know an electron has spin and we can determine its magnetic polarity using the right hand rule we can examine a crystal which is in caous and see no magnetic property. Applying a field to establish an orientation of the spins will produce a magnetic polarization.
First installment more to come..............

Sunday, November 17, 2019

Another look at the Transistor Universal (Amp) P or N

We start with a general purpose transistor and 4 resistors. The resistors I'm using are 100k, 10k, 4k7 and 511. I use these because they are what I have on hand you could use what you have within a reasonable amount. As we look at the circuits you will see how critical the values are.

First we establish the DC bias. R3 and R4 set the base bias. R2 sets the emitter bias. R1 is the collector load resistor. Connecting the Vcc completes the DC circuit.

Adding the capacitors provides the AC circuit. I marked the possible circuit connections. The The base cannot be the output and the collector cannot be the input. We connect the signal to the input and the load to the output. The third capacitor goes to ground (-Vcc).
Completing the circuit we have a battery and signal source. Time for some sim's.
Input base, output collector and ground emitter.
Input base, output emitter and ground collector.
Ground base, input emitter and output collector.

You may see the circuits drawn differently. Compare these three. In all three the base is grounded and the input is on the emitter. I downloaded these next three to show other variation.

So all we need is 4 values of resistors and a general purpose transistor to establish a basic amp stage with DC bias. Three capacitors to set the AC circuit response. The 2N3904 is a good general purpose transistor for hobby work. It will work in circuits up to 100 Mhz. You can look at the post on TUN and TUP circuit to see the tables of transistor you can use.


Saturday, November 16, 2019

Built an amp using the TUN design to see how it performed.

A piece of formica counter top and some copper tape can be used as the circuit board.

The back of the board will take glue better but the circuit shows better with the white background.

It is just a matter of leaving a little space between the strips.

Use an exacto knife to cut pads for the components to tie to. The two bigger strips are the power connections.

The white back ground helps you see the desired results.

It's just a matter of matching the pads and power connections as displayed in the diagram.

Here I used a piece of wood. I coated the wood with some glue befofe mounting the copper tape.

This is the amp with all the parts mounted. I used surface mount parts except for the transistors. You can use wired components if you like.

I connected power and set the input to produce 1 volt on the output. The input was about 40 mv.

The sim shows the schematic and the expected results. The circuit produced a little higher output than the sim predicted.

If I can do it anyone can.