crystal radio step 2

Resonant circuit.

If the link works it is a parallel resonant circuit.
When you space two conductive plates close together but separated by and insulator it forms a capacitor. Place a voltage across a capacitor will put a chatge on its plates.
When you pass current through a wire it creates a magnetic field. Twist the wire into a coil and it will make a stronger field as the field around the loops aid each other.
Put a coil and capacitor in parallel and pulse the circuit with a charge and the coil will send a charge into the capacitor. The capacitor will send energy into the coil. The cycle would repeat forever with perfect components. In the real world we have losses which must be overcome so the peak will decrease with each cycle.
The Q of a coil is the ratio of it reactance to it DC resistance. This is also the gain you can expect to see in a tuned circuit.
To recap a coil stores energy in a magnetic field and a capacitor stores energy in an electric field. Put them in parallel and charge the circuit and it will oscillate. The frequency at which it does is the resonant frequency.
Next post back to the calculator.

Making a crystal radio - the new project

I'm going to try a crystal radio design. Step by step with the benefit of a design available on the net and some tools also available on the net. The first step is to download the calculator.
Coil design spreadsheet
Read the note on page 1. The author allows sharing as long as he is credited.

The second step is to choose a capacitor. For this design we need a dual variable air capacitor. You could use this one.

The important thing with the capacitor is its range. The one pictured is 20 - 540 pf which is 540 / 20 = 27. The tuning range will be the square root of 27 or about 5 : 1. The capacitor is at its highest value when the frequency is lowest so if 540 pf = 500KHz 20 pf would equal 5 X 500 KHz = 2500 KHz. This is assuming no stray capacitance in the circuit. In the real world we could expect to see 20 pf of stray capacitance. Allowing for that we would see an actual 560 / 40 = 14 and the square root 14 = 3.7 tuning ratio. In this case if the low frequency is 500 KHz the high would be 1850 KHz. This would cover the MW band so would be good to go.
The other supplier's offering is supposed to be a higher quality with a range of 15  - 450 pf. How does the math work out?

118.5 Mhz receiver butcher

I added two chokes, changed the input  and changed the diode polarity.
Other than that it is as posted on TRB.
The post ahead of this one needed some resistance in the plate circuit and this one needed some reactance. First we get the DC bias correct and then we add the AC components.  Bypassing the source resistor and loading the drain for AC signal conditioning.
EDIT:
I was asked about a good reference. This is where I started:
radio course
The course is bundled in one file. It may take a while to download. 960 pages of electronic data.
EDIT2:
I lowered the value of the coupling caps. Check here to find out why.
Capacitor acts as a coil?

Vacuum tube loading -resistive vs inductive

A couple of things to consider about loading.

It is more about current than voltage swing. The slope of the static load line is determined by the wire resistance.

 I measure a 1 pie choke and it is 200 Ohms. Yes it has inductance and resistance.

Early tube radio schematic and theory of operation

Early radio data
In the old days before schematics had been standardized this is what we had to work with. Actually this book introduces the symbols to be used in schematics in the book.

How to wind a ferrite antenna

This subject comes up now and then so I am posting the data for when it is needed. Back in the good old days we didn't buy litz wire we made our own . That is the appeal of this unit, it used plain wire (make your own litz).

You need a ferrite rod, some 0.0028" wire and some paper to make formers with. What is this 0.0028" wire?

45 gauge or 0.071 mm. You cut 19 pieces of wire long enough to wind 64 turns and tie a knot on one end. Put that end in a vice or pair of pliers a helper holds and the other end in a drill. Stretch the wire out straight and spin the drill. Gently pull the wire to set the twist in place. You are now ready to make the coils. Cut a strip of kraft paper for the coil former. If you have double sided tape it is good to make formers. Just put a strip of the edge of your pare strip and wrap the strip around the rod with t he sticky side facing out. Fold the strip back at the edge of the tape and trim it with a sharp knife or razor blade. The MW sectionis ready to wind.
The LW former would be made in the same manner and then have an o-ring placed on each end to build a 'dam' to hold the wire in place as it is would.

It's a starting point even if you don't have the ferrite. I have a 6" rod to adapt. I haven't had much bench time lately so I have found a project.
EDIT:
Use the process from this post and make your coil then add the core to make a variable inductor to use with fixed capacitor.
Making a coil for IF or RF
Edit 2: Glue the ferrite to a threaded rod or use a copper or aluminum screw to make this one.
making a variable inductor

With so many possibilities just build something!

40/80 update

 This is the Audio Amplifier board. Looks good to me.

The crystal controlled oscillator using a a logic gate. It looks good to me. He said," not much to look at but works well.".  It looks good to me but I'm not a professional builder.
I had these in my folder with the rest of the design and decided to share.