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.

Thursday, July 22, 2021

Variable inductor controlled by a pot.

 A weird idea bouncing around in my head. It goes like this: I can use a pot and diode to acts as a variable cap. Why not use a pot and coil to act as a variable inductance. We have magnetic amplifiers which are basically variable inductors controlled by a signal applied to a control winding. On to the sims.

A simple 2N2222 oscillator. This one does not seem "strong enough". I think we need more output to drive our DBM.

The lambda diode oscillator is much stronger. Could be a good choice.

Ok , now we need a control winding and an out put winding. 

The sim supports the theory.

The sim supported the theory using Andy's oscillator. I wound a core with 3 coils, 1 turn, 3 turn and 16 turn and got the values I was looking for.

Time for a build when I get some bench time?


Thursday, July 1, 2021

Converting the Andy Osc to a GE transistor

 My young advisor looked the previous post over and gave me two points to consider. The transistor I used was an audio transistor which is not capable of operating at RF frequencies and we should consider using GE diodes with the GE transistor.

Both points are well taken. I do have some transistors to try but am woo-ful-ly lacking in data and the SPICE models. I did find I have a model for the P416 RF amp.

The original circuit.

The AC128 appears to work well. Sadly it has a very low Ft.

Still functions with one 1N34.

Second 1N34 'breaks' the circuit. Why?
Consider the voltage drop across the 220k resistor.

The current is to high and the 220k resistor is dropping to much. Let us try a smaller resistor.

OK. the 10k resistor restores our circuit operation. 
Next step is to find a suitable core.
I have a green core (43) that should work in the short wave range. The coupling being tight we will have to observe the loading effect. That will be the next post.

Monday, June 28, 2021

The Andy oscillator low voltage version

 My friend gave me two versions of this oscillator to use in the 40/80. They both gave a flat output over their operating range. I have a 6 volt lantern battery which was damaged (dropped I suppose). I took it apart and found one cell was shorted. The connecting strap was against the zinc shell. So I have 3 1.5 volt cells about half again as large as a D cell. I'm thing a 1.5 volt radio. A direct conversion receiver with an oscillator feeding a DBM and a a hearing aid amp audio section. 

This is the original circuit.

This is what I'm starting the build with. I am using a germanium transistor for 1.5 volt version. 

The number 1 issue with the direct conversion set is the oscillator will feed the antenna so I am thinking a ferrite core to help reduce undesired coupling.

Time to try a build.

Sunday, May 9, 2021

Using a piezo element

The High Z element will require a high voltage low current drive. To control the frequency response we must adjust the coupling caps and the load resistance. The high R high C circuit gives good low frequency response but drops off on the high end.

Lowering the load resistance flattens the response.
Lower coupling caps cause the low end response to drop off. This will make a 'tinny' sound.      

Thursday, April 15, 2021

Turret board amp upgrade.


I will use the double row layout. First step is to layout the components.

I laid it out in spice so i could test the circuit. The sim works so I didn't miss any jumpers or cross fed any points.

My first build worked very well but left room for improving the layout.

I may want to put it in a box. The components on both side and the transformer mounted on the turret pins will not fit a box well.

This will install in a box much easier. The transformer on a separate board will allow it to be placed so the jack is accessible.

The little amp works nicely with a DBM.
I wound 9 turns of 3 strand wire. One coil is the primary. The other 2 form a tapped secondary. The taps are the AF output. RF and LO feed the primaries.
The platform is a pill bottle cap. The base is a piece of press board. I used turret pins to mount the diodes. I had the terminal strips on hand so I used them for the I/O connections. Turret pins would work just as well for the I/O.
This setup received a station in Texas and one in Tenn.
The 80 meter ham band was active.
WWV on 5Mhz.
Several shortwave stations around 6Mhz.
This was using my bench signal generator as the LO. Next step would be to build a generator.

Monday, April 12, 2021

Amp, Coil, Turrets, Board

 Had a little shop time. (rainy day) 

Took the lid off an ice cream carton and made a coil form.

I squared the material, Wrapped it around a suitable round mandrel. When heated the material melts and is sticky. (Think hot glue) I used a heat gun (hair dryer) to fuse one end. Pushed the form off the mandrel so it didn't stick to it. Fused the other end in like manner. Then fused the seem length wise.

I wound the coil with the wire on the bench. Then finished the coil with a dope made from ping pong balls and finger nail polish remover.   

The plan was to make a turret board for the amp build. This material is readily available and perfect for the job.

Look familiar? You will see it in the kitchen and bath. (If you do not have stone counters tops.) Formica was invented to be used as an insulator. It also makes some fine counter tops.

The plan is to use a turret board, These are ok but a little pricey. The formica is left over from a kitchen rebuild. The turret pins are 1 - 2 cents each.
Here are some examples of the turrets.

Here is the drawing for my amp. I used the scrap which was about 1" wide. I made 3 rows of pins. In the future I will spread the circuit out more. But I just used the piece which was already cut.

The pins were double ended so I put parts on both sides of the board. The little amp sings. It drives my earbud with the output of my AF generator all the way down and the 20db attenuator on.

I added a V cap and diode with test leads and it picked up a station which IDed itself as being 600 miles away. The prototype performs well. I will likely make another on a bigger board.

It may be worth looking into the formica. Last I bought was about $50 for a 4' by 8' sheet. Less than $2 a square foot is not bad?

Tuesday, April 6, 2021

Adding a pot to spice.

 symbol file .ASY


Version 4
SymbolType CELL
LINE Normal 0 -36 0 -48
LINE Normal 0 48 0 36
LINE Normal -20 -3 -9 0
LINE Normal -20 3 -9 0
LINE Normal -20 3 -20 -3
LINE Normal 9 -36 0 -36
LINE Normal 9 36 9 -36
LINE Normal -9 36 9 36
LINE Normal -9 -36 -9 36
LINE Normal 0 -36 -9 -36
LINE Normal -32 0 -20 0
CIRCLE Normal -6 32 1 25
WINDOW 0 16 -32 Left 0
WINDOW 3 17 -1 Left 0
WINDOW 123 16 26 Left 0
SYMATTR Value R=10k
SYMATTR Value2 T=.5
SYMATTR SpiceModel pot
SYMATTR ModelFile ..\sym\EXTRA\Misc\pot.lib
SYMATTR Description Potentiometer
PIN 0 -48 NONE 0
PINATTR SpiceOrder 1
PIN 0 48 NONE 8
PINATTR SpiceOrder 2
PIN -32 0 NONE 0
PINATTR SpiceOrder 3


Model - .lib file.


 .SUBCKT pot 1 2 3
.param tap=limit(T,.001,.999)
R0 1 3 {R*(1-tap)}
R1 3 2 {R*tap}




The ASY file defines the lib file location. Spice will look for the lib file in your lib directory. To allow spice to find the file either place it in the lib directory or modfy the line in the ASY file to locate it.



Monday, March 29, 2021

Sunday, March 28, 2021

The amp response


Click EDIT
Click SPICE Analysis
Fill in the 4 blanks to define the sweep.