Copasetic Flow

  I follow both SolderSmoke and Ham Radio Work Bench, so I've been avidly watching the SolderSmoke driect conversion reeiver challenge thrown down by Bill Meara. Bill's said something for year's that's intrigued me: you gotta be able to understand how an RF mixer works. That was paraphrased, of course. I haven't had much success along those lines until today.  Looking at the Wikipedia entry for Frequency Mixers, I bludgeoned my way through the diode section, and I finally get it. (OK, I'm a little miffed that I have to take on faith the expression for the current through an ideal diode, but I can let that slide for the moment.) Lo and behold, after a series expansion and a binomial multiplicaiotn, there was the promised expression for the sine of one frequency times the sine of another. Using a high school trig identity, that can be rewritten as a sum of waves one of which is the sum of the two frequencies and one of which is the difference. That's not al...

 I made one QSO, was heard in Costa Rica, and maybe found a wavelength tall natural antenna tower in Albuquerque. Here's a view from below of the mesa the POTA station was situated on. Park: Petroglyph National Monument POTA  K-0955 . Radio Details: Radio : RockMite 20 Antenna : Halfwave dipole Happenings of Interest   Shyoooo, I was tired. I spent a few minutes debugging the lack of audio when I turned on the radio. In the end, the answer was...... I hadn't plugged in the headphones. I was so tired. It's been a week. Here's the thing though: the antenna was 5.5 ft off the ground during most of the POTA. And, as you might expect from reading any number of ham radio books that exhort the amateur radio neophyte to build a tower as soon as possible, I only made one QSO, to a station a few blocks away. (Actually, I thought that was pretty cool! That might have been the shortest QSO the RockMite ever made.) As you might not have expected—I certainly didn't—the radi...

In studying form my EM midterm, I came across a practice problem involving finding the potential along the z axis due to a charged disc centered on the same axis.  After thinking about the problem a bit, I turned to what's becoming one of my favorite online references, Dr. J.B. Tatum's text on electricity and magnetism [2].  Sure enough, there was a solution that could be adapted to the task at hand.  It involved several 'clever' trig substitutions one of which were not immediately clear to me, so I've expanded upon it here.  After the clever trig trick, read on to find out more interesting stuff about Dr. Tatum, an emeritus professor at the University of Victoria [1]. The Basic Problem The practice problem mentioned above is described by the following diagram from Dr. Tatum's text.  The first and handiest innovation in Dr. Tatum's treatment is to parameterize the problem using the angle marked as theta and the limit of that angle labeled as alpha. T...

Just a few random thoughts on why I wish I'd done a better job of memorizing my trig identities in high school. Here's an approximate high school conversation of mine regarding trigonometric identities with my teacher Mr. Tully, (who is awesome and by the way, who is also a rancher, and also by the way is not the guy pictured to the left(picture 1)... read on!) Me:  "Why do I have to memorize these 40 or so trig identities [2]?" (yes even then, I referenced my utterances" Mr. Tully:  "Because they'll be very important for what you want to do later." (he knew I wanted to be a physicist) Me, (typically not thinking 'later' might be after next week):  "Yeah... I'm not seeing it..." Fast forward a bit to grad school.  Twice in the last week, trig identities were make or break features of homework problems.  I didn't pick up on the necessary identities in electromagnetism, and I'll probably get a B instead of an A ...