### Getting started with PSK31

I saw a great presentation on PSK31 using the nue psk portable modem at the Mesilla Valley Radio Club this past weekend. The Nue PSK modem let's you get on the air with PSK31 without a computer. It uses an on-board micro-controller to handle the modem operations and includes an LCD for the waterfall display.

It occurred to me that my Windows Mobile enabled phone also has a programmable processor and a decent LCD display, so I went searching for PSK31 software for the Windows Mobile platform. NT7S quickly pointed me to Pocket Digi. It's a great little program that was easy to install and use! So far I've been able to decode psk31 just by placing my phone close to the speaker of an HF rig and selecting QSOs on the waterfall display.

On my Treo phone, I did have to do one quick little workaround. I first open the Windows Media Player and play any song. For some reason, this alerts the platform or the software that the speaker and microphone exist. If I don't do this, PocketDigi wakes up and complains that it can't access the microphone on the Treo.

Nobody heard me last night on transmit. On the chance that the issue is caused by my headphone speaker being used as the input to the PTT microphone, I went searching for audio-out to mic-in circuits and found this great page by G4NSJ with lots of interface circuits and info.

Have fun!
73 de KD0FNR

Jason NT7S said…
Glad to have assisted you with the PSK app. Hope you can get that thing transmitting and I can catch you on the air sometime.

73 de NT7S

### 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…