Sunday, October 31, 2021

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.


Friday, October 29, 2021

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?


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.