Ham Radio General Class Lesson 3.4, Technical Standards


This is your video introduction to Lesson 3.4 in the ARRL General Class License Manual. The material in the text is actually quite short, so I provide some background information to put it in context.

This entire paragraph is a side comment: In the video I mention there’s no such thing as negative power. That is in fact true of resistive loads, but not of reactive (inductive or capacitive) loads. There are two measures in the case of a reactive load. First, the “volt-amps,” which is the voltage times the current. Then there’s the power factor, which is a function of how reactive the load is. It’s a fraction between 0 and 1 and is mathematically the cosine of the phase angle between the voltage and the current. (Am I telling you that voltage can go one way while current goes another? Yes, I am, but don’t let it keep you awake at night.) You multiply the volt-amps and the power factor to come up with real power. Electrical utilities do not like reactive power because it loads down the system but doesn’t buy them anything (they sell watt-hours, not volt-amp-hours). In most cases, utility loads are inductive (the coil windings in motors, for example, are actually inductors). So the utility adds capacitance here and there to balance out the load. If that sounds really weird, don’t worry, it’s not something you need to know to pass your test, but I just thought I’d throw it in for completeness.

When you are done with this video, click here to return to the list of introductory videos.

This entry was posted in General Class License Training, Ham Radio blog entries, Video and tagged . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *