“The Electronics Of Radio” NorCal 40B Transceiver Build Lab Notes: Problem 21

February 8, 2026 by KM1NDY

This continues a series of blog posts on David Rutledge’s text, “The Electronics of Radio”, that I am studying while building the NorCal 40B transceiver. This series of posts will not be a review of the book, nor is it a assembly manual. Rutledge presents a series of problems at the each chapter that aid in understanding electronics and building the 40M QRP CW transceiver. I am going to try to go through all of these problems and document them here. All of these are titled similarly, so search for them that way. For what its worth, most people will want to skip these posts, they are really for my own self-education on electronics and may not make a lot of sense unless you have Rutledge’s book.

[The links to all problem solutions as I go through them will be posted here.]

Note: The circuit for the NorCal 40B is slightly different then that for the NorCal 40A. I added C56 (47 nF ceramic) and C40 (10µF electrolytic) capacitors based on comparing the two schematics.

Note: DO NOT remove the 1Ω resistor between SW1 terminals from Problem 20 for this problem.

Note: Add a TRS-TRS audio cable into Key Jack J3. Use an alligator clip jumper lead to short the tip of the free end of the audio cable to the ground of the circuit.

Note: The power cable I used is a cannibalized from an old 9V wall wort with a barrel connecter that fit the one on the NorCal 40B. I cut off the wall wort and exposed the positive and negative wired, tinned them with solder, and am using alligator clips to power the circuit with my desktop power supply,

Note: I am starting with a 10V 100mA DC power supply setting.

R12 measures 21.64Ω once soldered into the circuit.

The components of the Problem 21 are soldered on, and the measuring, signaling, and powering equipment is placed in the appropriate locations.