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### The Rockmite 20 at 10k

The Rockmite is back up and running! After replacing the 2N2222 that amplifies the transmitted signal I hadn't made a contact in a week or so, and I was starting to think I'd smoked yet another component. I decided maybe a better antenna location would help. The weather was exceptionally warm in Boulder today, so it seemed like the perfect time for a hike. I packed up the rig, my fishing pole, and my antenna and headed for Lefthand Reservoir in the Roosevelt National Forest outside Ward, CO.

The temperature was quite a bit colder at altitude, (Lefthand lies at about 10,700 ft.), but the hike was pleasant and pretty easy. There's not a whole lot of snow yet and the trail to Lefthand lies entirely on a Forest Service Road that's closed for the winter. The reservoir was completely frozen over, so fishing was out, and I set up the Rockmite and its antenna right away.

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I hung the half-wave dipole about six feet up to start, turned on the Rockmite, and heard... a crystal clear CQ from W9FFU! I responded and W9FFU promptly called back with an RST of 449! I haven't operated in the mountains before, and the signal quality just stunned me! There was no static and no interference! The little Rockmite was reaching all the way to Oak Harbor, WA on half a watt!

I'll be back up tomorrow, November 17, 2008, between 17:00 and 20:00 GMT if you'd like to chat. The frequency should be around 14.060 MHz in the QRP portion of the band.

### Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

### Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr.

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

### Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…