OVMRC Course – Week 9

This Week:

*AC theory test & review
*Power Supplies by VE3EJJ

This week’s session started with an informal test of our AC theory knowledge. I really like the fact that the course provides for these tests of knowledge as I believe that the more practice you have at writing them, the more you can identify as areas for review.

Being that I am focused on studying for the Advanced certification, I found the test to be an excellent review and did not struggle with any of the material. I did however manage to confirm that I (as usual) need to take my time and ensure that I select the answer I intended.

An extensive review of the material ensued which I hope helps those who have some technical theories that they need to master still. Some of the questions seemed to come from nowhere, for example the dB math, however, it just shows everyone what they need to focus on.

I really hope that the worked examples mini-book that I am working on helps people with some of this material.

After a brief break, Ernie (VE3EJJ) gave an excellent introduction to block diagrams and power supplies. I always come away from each night with a hand-full of things I learned, and tonight was no exception. I now appreciate how finicky electronics can be, especially the bias of diodes in a bridge-rectifier circuit.

As usual, Ernie had a very well thought out demonstration for everyone. He built a miniature bridge-rectified power supply, complete with filtration! Using an oscilloscope, Ernie demonstrated the wave-form of a half-wave rectified circuit, the full-wave rectified circuit and a filtered output. Bravo to Ernie for always having excellent demonstrations for the class. I imagine he spends quite some time on preparing them!

Oh, and on a technical note: if things look screwed up on your oscilloscope, check for foreign grounds! Ernie had to isolate the scope using the 2-pronged output from a trouble lamp. Bob (VE3SUY) was helping Ernie and hooked the trouble lamp to the scope’s metal support legs (as any of us would have done) … and well, that reintroduced the ground problem Ernie solved with the lamp. It took a few minutes but Ernie figured it all out as we wrote the practice test.

On a social note, Bob let everyone know that Carleton University is selling off some older HP oscilloscopes for a great price. Ken (VA3NEK) reminded everyone that you can also bid on Government surplus (read: oscilloscopes, function generators, etc) from Crown Assets. I’ll have to check that out!!

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