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.......