Friday, October 8, 2021

Update on 1.5 volt receiver

A question about this circuit started me looking at it. It uses a 9 volt supply but why? The audio amp and Vcap tuning require 9 volts. The detector uses 1.4 volt.



 Using this portion of the circuit with my 1.5 volt hearing aid amp give good results. 

I would substitute a 200 ohm resistor for R1 and use a lower value pot for the regen. My test determined R2 could be around 10K. With the 100k pot it operates close to the pots low limit.

I did assemble the DBM and Lambda Diode set. That is still an option.

I am considering a discrete component Gilbert Cell. While this is a good option it would require a higher supply. 

Someday maybe the Gilbert Cell, Lambda Diode, and earbud amp will find their way onto a board. The Lambda Diode does not need a tapped coil so it would be possible to make a socket to use plug in coils. The Gilbert Cell provide conversion gain. This could be the beginning of an all band receiver. It could use one Vcap and plugin coils.


Some food for thought.



Tuesday, September 21, 2021

Adding a Lamda Diode Oscillator and V-Cap

 

The four transistors produce a Vcap to tune the oscillator. The sim is stepping the 10k pot from 1k to 10k in 1k steps. The 100p cap (C2) set the range while the pot produces band spread. If C2 is a variable air cap you could tune with it and use the pot as a band spread. You could use a switch to select C2 as a band selector.

* I need to do some adjusting on the circuit but this is a good start. Putting it here so I don't loose it.



Friday, September 3, 2021

3 volt earbud amp

 Back to the project. I will be going with the 3 volt supply. My earbud is rated at 1ma. This amp look good.



The input is 500uv for 1 ma output. 

The battery drain is a little less than 1 ma. R6 could be adjusted to vary the Q current. If R6 was 1 meg it would probably be good but for I'll go with 100k and expect to need a volume control. 

Time to clean off the bench and gather parts for a build.


Tuesday, August 31, 2021

RF resistance data

 I'm putting this here so it does not get misplaced.






Monday, August 30, 2021

Consider the dualities. The opposites. What can we say about them? light - dark E field - H field particles at rest or in motion.


 Consider EMF, current, B and motion.

Can we have any of them without the other?

Suspend a wire in a H field and send a current threw it, it will try to move.

Suspend a wire in a H field and move the wire OR magnet, you will produce current in the wire.

Passing a current threw a wire produces a magnetic field. Can we have a magnetic field without current flow?

Consider the permanent magnet. It has closed loop currents in it structure which create the field.

Question: Can we have a "permanent E field"? Not a trick question so disregard a charged capacitor and the Lydel jar.

A bar magnet has a "permanent H field".

Can we have a "bar ????" with a permanent E field?

What if we melted a bar of wax and placed it in a strong E field and let it cool. Would the field effect the wax?

Can I use wax as the dielectric in a capacitor? Yes of course I can. Will it make a stronger capacitor? Yes it will. Again, what happens if I melt the wax and let it cool while holding a charge on the capacitor?

Hint: Consider the Electret Microphone.

 Notice the relationships in the right hand and left hand rules are all at 90 degrees. Also note one component is force/motion. With a generator we turn the armature to create current. With the motor the current causes the armature to spin. Can we have motion without a spinning armature? Consider the transformer. The motion in the primary is "current" flow. The motion in the secondary is also "current flow. 

 Note: In the beginning (when I was young) it was "H" field and "Cycles Per Seconds". Today they prefer "B" and "hertz" so I may at times use an unfamiliar term. I will even switch back and forth now and then.



LDO low voltage - pinned vs surface mount components

I was planning a single cell radio. The previous oscillator was looking good but will need a little more thought. In the mean time I am looking at the LDO for the single cell radio. My parts bin is fairly well stocked but I am having to decide between surface mount, pinned component or using 3 volts? (the original plan was 1 cell) This series of post show the options.


3 volts both pinned
2 volts both pinned.
1.5 volts 1 surface and 1 pinned.
2 volts both surface mount.
2 volt 1 pinned 1surface mount.
1.5 volts 1 surface 1 pinned.

So I can obtain the goal of a 1.5 volt LDO by using 1 surface mount and 1 pinned Jfet or I can move the goal and use 2 cells.




Wednesday, July 28, 2021

A little mind experiment about the coil - core - inductance relationship.

Q - What is the "Q" of a coil?
A - The quality of the coil.
Q - OK? Plain English please.
A - The reactance and the resistance divide the energy. A pure reactance has no loses. A pure resistance has a power factor of 1.
Q - OK? So what is the power factor?
A - Pure reactance PF = 0. Pure resistance PF = 1.
Q - How do we determine the PF?
A - We would use vectors or phasers or trig factors.
    The simple math for Q is X / R. So if R = 0 Q is infinity. This is why the wire size, wire type and core material matter.
    
    
    Now on to the mind experiment part 1:
    Assume we wind an air core coil for my oscillator. It would have a Q determined as any other air core coil. Assume we set the circuit to oscillate at 4 MHz. All is well but it is fixed frequency. Now I want to lower the frequency by inserting a ferrite core. As I insert the core the frequency lowers. Assume the frequency changes to 3 MHz. This would be a small change from 30uh to 15uh with a 100pfd cap. What happens to the Q? Remember Q = X / R. The wire has not changed so R remains the same. The core causes the X to increase so Q increases.
    
 
    Now on to mind experiment part 2:
    Here is the real question to consider.
    The air core coil is 15uh.
    The core raises it to 30uh.
    I place a magnet against the core and it saturates, what happens?
    The relative speed at which the field expands or contracts is the variable.
    Consider the speed of sound in air and in water.
    Consider the speed of light in air and in water.
    When we place a straw in a glass of water it appears to bend, why?
    The basic laws for motors and generators tell us the field strength and relative motion determine the motor input requirements or generator output.
    
    Mind experiment final:
    The air core core has a Q of some value.
    The metal core has a higher Q.
    Assuming the air core Q is high enough for our circuit inserting the core should be ok.
    Saturating the core makes the core become "invisable" or in other words it will make the coil to act the same as the air core version.
    
    So in theory can I adjust the oscillator frequency by adjusting the bias on the core.