Friday, February 12, 2010

KML to Lat/Long Array in Ruby

Several of the next applications of the qrpTracker codebase will require me to draw rudimentary maps on an LCD screen. I've been using Google Earth's polygon tool to make polygons that roughly correspond to, say, Prince Edward Island (in the small scale) and North and South America (in the large scale). Google Earth will allow you to copy the corresponding kml fragment. The following code snippet will turn that kml polygon into a C array of two point arrays, suitable for storing in your Arduino as Progmem.

Wednesday, February 10, 2010

Building the AA2TX Parasitic (Or 'Passive') Lindenblad for 70cm

The AA2TX parasitic lindenblad, which was published in Feb 2010 QST (and has been available online for some time), is proving to be an enjoyable project. I have modified some components because I could not find them here in Atlantic Canada. The #8 aluminum wire for the passive elements is not in our big box stores (different wiring regulations?), and the PVC ferrules require a special order, at least at this point in the year, when no sane person would be installing eavestroughing. So I made do with what I had, and the results are encouraging.

Thursday, February 4, 2010

More on Linear Transponder Calculations

In my last post on the subject, I'd concluded
The result is that for non-inverting transponders, the equation is this:
`up_o = (dl_o - bc_d + bc_u)/(1-v_r/c)`
For inverting transponders:
`up_o = (bc_d + bc_u - dl_o) / (1 - v_r/c)`
Soon after, I received a kind email from Tony AA2TX, with an offprint of his 1997 Space Symposium paper that describes the object-oriented computational approach  that is built into the InstantTune code.[1] Since I've been happily pillaging  the IT code for some time now, I'd noticed what this article confirms, namely that instead of using `(up_x) / (1- v_r/c)` to get the value of the origin signal from the received signal, InstantTune uses  `(up_x) (1+ v_r/c)`.

Tuesday, February 2, 2010

Satellite Audio Analysis

In a recent posting to amsat-bb, I asked if anyone knew of a way to grab the loudest-frequency and s/n data from an audio stream, thus saving for further analysis the data that Spectran shows in realtime over its waterfall. It seems this isn't an easy question to answer, so I did some more digging and came up with the following candidates.

Monday, February 1, 2010

Calculating Linear Transponder Uplinks

As previous posts show, my sattrack code is working fine with uplinks and downlinks that do not have any interdependence, such as beacons and FM satellites. For linear transponders, I used a simplistic approach that was not giving good results, so I hit the books over the weekend to derive formulas that will determine the source uplink frequency (at the radio) for a given downlink frequency. In the following, I'm using the definitions of Davidoff, chapter 8.