“The Electronics Of Radio” NorCal 40B Transceiver Build Lab Notes: Problem 5D, 5E, & 6

May 10, 2025 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.]

PROBLEMS 5D & 5E:

First off, I set up my relatively new power supply, the TekPower TP-3003D-3 0-30V/0-3A, to output +12 volts and -12 volts using the configuration shown below. As a slight aside, I bought this particular unit because I have a strong affinity for the Kaito Pocket Radio. This little radio kept me company on the 140 miles or so of the Northville-Placid Trail hike AA1F, Nellie, and I did many years ago now. When I found out they made power supplies, I thought they would be good given how much I enjoyed their radio once upon a time. Remember, I am sponsored by nobody. It’s all just my own stuff I talk about. So far this power supply is working well for me.

Next I set up the circuit as instructed, simply a 2N2222 transistor attached to two 2.2kΩ, one at the base and one at the collector.

The +12V supplied the collector and the -12V supplied the emitter. The function generator, set to a 100-kHz square wave and starting at an amplitude of 100mVpp, was inputted into the base. I am using Channel 1 (which is the yellow writing at the bottom) for this test. You can see one of my new BNC tee connectors splitting the output signal to the oscilloscope directly and to the circuit (as instructed).

The function generator voltage is increased until increased until significant voltage gain is identified at the collector output on the oscilloscope.

The top trace is actually the input square wave and has an amplitude of 1.3 volts (which is essentially the same as what the signal generator claims, i.e., 1.28V).

The bottom trace is the output waveform (from the collector) and is actually 2.35V. If multiple channels of the Tektronix 2465 oscilloscope are in use, the display only shows the voltage of channel one. So I needed to turn off channel one to read the voltage of channel two. The output waveform looks quite distorted.

The signal generator voltage is reduced and a 1mH inductor is placed between the collector resistor and the +12V power rail.

Turning up the signal generator to 1.28Vpp so the transistor turns on shows this collector output waveform (bottom trace).

The maximum fluctuation of “ringing” voltage is 7.02Vpp.

An 1N4148 “snubber” diode is added to the circuit in parallel with the inductor.

The parallel snubber diode results in the ringing voltage being much less than without it. From the book: “The snubber diode limits the voltage across the inductor to the forward voltage of the diode.” Of course this would mean that the maximum “ring” of the ringing should be around 0.7V for a silicon diode. Unfortunately I did not measure it.