A coax maker explains the Z here

 Just putting this here before I misplace it.

 

https://www.clooms.com/50-ohm/

 

 

What determines coax Z. What determines twin lead Z? Is all coax 50 Ohm? Is all twin lead 300 Ohm?

 These scans from the calculator should tell the story.

It appears to be a matter of construction. So why 50 OHMs?

Z matching? Some points to remember.

 The old saw is to obtain max power transfer you must match the source and load Z.

The part that is left out is WHEN Zin = Zout half the power is lost in the generator!

Consider the 1000 Mega watt power generator feeding the grid. If it was Z matched HOW WOULD THE GENERATOR SURVIVE 500 Megawatt. The answer is it would not. The wires would melt and the flash over would be exiting. I saw this once. Thankfully the lead is a fusible link. It produced the flash in a confined space.

Anywho, Just look the sims over and see if it make since.

the delay produced by the Tline with matched Z.note the 50% signal loss.

lower the gen Z and the output increases. matching.uh?

Raising the load Z is not so good.

A lower gen Z reduces losses. Look at the rise in output.

If matching ALL of the circuit only losses half the signal what is the Tline Z?

In other words the Tline is 50 Ohm? So why is there no loss produced when I insert the Tline?

Hint: The Tline is not resistive.

Hint: The Tline is not a flat 50 Ohm. Actually it may vary much more than one might think.

So when they say the Tline is 50 Ohm what does it mean?

Maybe more on this later?

Single supply op amp in sim

 

Single battry supply for an op amp

Using an op amp  for a simple radio. Single 9 volt supply. An example of how to "split" the supply ans create a reference for the inputs.

 

https://radio.radiotrician.org/2016/08/op-amp-radio-update.html

 

Active antenna for shortwave

This little circuit is a start point for an active antenna.

I labeled some tie pints to help with the hookup.

The gain is good.

Look at the current drain. (as designed)

Subbing a J112 increases the current drawn but the gain is still about the same.

Checkout the frequency response. My target is 3 - 10 meg. Ok for that range? Using a J112 here.

Using the 2SK2539 reduces the current draw. You could use any JFET but the performance will vary.

What would happen if we vary R13, R14 and C9?

What would happen if we vary R16, R17 and C12?

Does it need a RF gain pot?

 

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.