For fun, I downloaded cocoaModem: a program that decodes many modes, including RTTY, PSK31, and SITOR-B. SITOR-B is similar to RTTY, but is used by the USCG to send out weather alerts to ships at sea. It took me a few tries, but I finally got the hang of it (it’s a little odd compared to fldigi, which seemed straightforward, but which sadly just runs on Linux, not my macbook), and here’s a screendump of it decoding:
Tom Duff recommended this blog for my perusal, and I filed it away. Today I discovered that it was linking back to one of my more popular posts: the one in which Tom Duff talks a little bit about Duff’s device. But there’s a lot of good reasons to check it out. I found this post about Unix viruses, which contained a link to one of Tom’s papers that I never read, although Tom and I have discussed at various times. Very neat. Lots of other good things in there too! Worth reading.
Here’s another NOAA 17 pass, recorded on a bright and sunny Saturday morning. I tried a bit of a different setup this morning: I was using a small preamp between my Yagi and my trusty rusty Pro-60 scanner. As you can see, an otherwise gorgeous 86 degree pass was spoiled by some interference. Can anyone tell me what they think it is? It’s obviously synced on a 1 Hz period.
The preamp might have actually helped in getting the last 100 or so scanlines.
Addendum: While the interference that we see is serious, the broad horizontal streaks that cross the entire image are actually due to a bug in my sync detector. I’ll have to work that out.
Addendum2: Mike, WA7QPC had an explanation for the interference patterns that I am seeing. He sent me the following picture:
Looks pretty familiar, right?
From Mike’s email:
I’m attaching an image I received with a Timestep Proscan weather satellite receiver, which is supposed to have the proper IF bandwidth, but even that is a little too wide, apparently. This image was received when there was no NOAA satellite in range, and the image was generated using WXSAT. I got around it by attaching an outboard IF amp and demod to the receiver. It has a narrower or sharper filter, supposedly a little too sharp for NOAA, but it works fine for me, and gets rid of the interference. Sorry the file is so large. For some strange reason, it doesn’t want to compress very well….can’t imagine why!
Apparently several Orbcomm satellites timeshare on one frequency, and every few seconds one will switch on or off, accounting for the pattern you see….and hear.
Thanks a lot Mike! Looking at the the table of frequencies that Mike sent me, the most likely interference source is the Orbcomm satellites, broadcasting on 137.663Mhz. If my scanner had the right bandwidth (say, around 50khz instead of the 200khz or so that the scanner has) then this noise source would be outside the band.
Addendum3: Thanks to all the members of the GEO subscribers group on Yahoo! for confirming Mike’s diagnosis. And yes, I know, I should be using a QFH antenna. 🙂
Eighteen long years ago was my first day at Pixar (before it was Pixar Animation Studios). Today, I’m celebrating by taking a bunch of my fellow Pixarians out for pizza and general good times. According to wikipedia, it was also the day that the Central Committee of the Soviet Communist Party agreed to give up its monopoly power, and the Soviet Union collapsed. Other events from that month: Nelson Mandela was released from Victor Verster Prison. Exxon was indicted on five criminal counts for the Exxon Valdez oil spill. Buster Douglas knocked out Mike Tyson. An agreement was reached to reunify Germany.
I was 25, about the same age as many of the kids I work with these days. I’ve spent nearly half of my life working here, and I must admit, through trials and tribulations, ups and downs, it remains a really, really terrific place to work, and I have been truly blessed with getting able to work with some of the most talented and nice people on projects that are truly amazing achievements in movie making.
To any ex-Pixarians I’ve worked with who have moved on, I salute you too.
It now can put out ground tracks as well as more detailed tracking information. Just a few more lines of code.
ARISS will be visible from grid CM87ux starting in 01:36:47 at 23:08:11 23:08:11 +0.0° 210.7° ? 21.8°N 132.1°W AOS 23:09:00 +3.4° 207.9° ? 24.2°N 130.0°W 23:10:00 +8.5° 202.5° ? 27.0°N 127.2°W 23:11:00 +15.8° 192.4° ? 29.8°N 124.3°W 23:12:00 +26.4° 170.1° ? 32.5°N 121.2°W 23:12:51 +32.2° 132.9° ? 34.8°N 118.4°W MAX 23:13:00 +31.8° 125.4° ? 35.2°N 117.9°W 23:14:00 +22.3° 88.7° ? 37.7°N 114.4°W 23:15:00 +13.0° 72.4° ? 40.1°N 110.6°W 23:16:00 +6.7° 64.6° ? 42.3°N 106.5°W 23:17:00 +2.0° 60.2° ? 44.4°N 102.1°W 23:17:31 +0.0° 58.7° ? 45.3°N 99.7°W LOS
P.S. Sigh, wordpress is apparently working very hard to get rid of the Unicode characters I nicely output. To the right of the azimuth/elevation should appear a sequence of arrows to indicate if you should look north, south, east or west. When I run this on my terminal, I get:
I’ll have to work on deciding whether this Unicode stuff is worth the trouble. Probably not.
Got on board the late night pass for the ISS, and right after that went down, turned around and worked SO-50. Sadly, the recorder I normally used didn’t pick up the passes, must have hit the stop button (annoying!). But I worked N6RSX via the ISS, then got KB7F and … rats.. memory… failed me… i heard him on the ISS too…. Mountain View, CM87, November… something… O… Sigh.
I’ve been reading up a bit on antenna design, particularly the design of Yagi style antennas, and decided to give it a whirl. In particular, I decided to try to design a Yagi that actually is supposed to work on 137.62 megahertz, to see what is possible. I actually am not displeased with the paper specs for the resulting four element 137Mhz Yagi. I designed it using the suite of programs written by David Kirkby, G8WRB. Here’s the resulting pattern at the design frequency.
Here is the specification for the resulting design…
NOTES Optimised with the genetic algorithm
FREQUENCY 137.620000
MIN_FREQUENCY 137.000000
MAX_FREQUENCY 138.000000
STEP_FREQUENCY 0.020000
ELEMENTS 4
DRIVEN 1
PARASITIC 3
ANGULAR_STEP 2.000000
#DATA_DRIVEN x y length diameter voltage(r) voltage(i)
DATA_DRIVEN 0.38625 0.00000 1.02524 0.00475 1.00000 0.00000
#DATA_PARASITIC x y length diameter
DATA_PARASITIC
0.00000 0.00000 1.08740 0.00475 reflector
0.95210 0.00000 0.94818 0.00475 D1
1.78574 0.00000 0.92937 0.00475 D2
And here is the analysis over the entire 137-138 Mhz band.
# Driven=1 parasitic=3 total-elements=4 design=137.620MHz # Checked from 137.000MHz to 138.000MHz. f(MHz) E(deg) H(deg) R jX VSWR Gain(dBi) FB(dB) SideLobes(dB) 137.000 58.1 79.6 28.25 -4.35 1.790 9.202 26.440 0.000 137.020 58.1 79.6 28.24 -4.22 1.789 9.205 26.547 0.000 137.040 58.1 79.6 28.23 -4.08 1.788 9.209 26.650 0.000 137.060 58.1 79.5 28.23 -3.95 1.788 9.212 26.750 0.000 137.080 58.1 79.5 28.22 -3.81 1.787 9.216 26.845 0.000 137.100 58.1 79.5 28.21 -3.68 1.786 9.219 26.936 0.000 137.120 58.0 79.4 28.20 -3.55 1.786 9.222 27.023 0.000 137.140 58.0 79.4 28.20 -3.41 1.785 9.226 27.104 0.000 137.160 58.0 79.4 28.19 -3.28 1.785 9.229 27.179 0.000 137.180 58.0 79.3 28.18 -3.14 1.784 9.233 27.250 0.000 137.200 58.0 79.3 28.17 -3.01 1.784 9.236 27.314 0.000 137.220 58.0 79.3 28.16 -2.87 1.784 9.240 27.371 0.000 137.240 58.0 79.2 28.16 -2.73 1.784 9.243 27.423 0.000 137.260 57.9 79.2 28.15 -2.60 1.783 9.247 27.467 0.000 137.280 57.9 79.2 28.14 -2.46 1.783 9.250 27.505 0.000 137.300 57.9 79.1 28.13 -2.33 1.783 9.254 27.535 0.000 137.320 57.9 79.1 28.12 -2.19 1.783 9.257 27.558 0.000 137.340 57.9 79.0 28.11 -2.05 1.783 9.261 27.574 0.000 137.360 57.9 79.0 28.10 -1.92 1.783 9.264 27.582 0.000 137.380 57.9 79.0 28.09 -1.78 1.783 9.268 27.582 0.000 137.400 57.8 78.9 28.08 -1.64 1.784 9.271 27.575 0.000 137.420 57.8 78.9 28.07 -1.51 1.784 9.275 27.561 0.000 137.440 57.8 78.9 28.06 -1.37 1.784 9.278 27.539 0.000 137.460 57.8 78.8 28.04 -1.23 1.784 9.282 27.509 0.000 137.480 57.8 78.8 28.03 -1.10 1.785 9.286 27.473 0.000 137.500 57.8 78.8 28.02 -0.96 1.785 9.289 27.429 0.000 137.520 57.8 78.7 28.01 -0.82 1.786 9.293 27.379 0.000 137.540 57.7 78.7 28.00 -0.68 1.786 9.296 27.322 0.000 137.560 57.7 78.6 27.98 -0.55 1.787 9.300 27.258 0.000 137.580 57.7 78.6 27.97 -0.41 1.788 9.304 27.189 0.000 137.600 57.7 78.6 27.96 -0.27 1.788 9.307 27.114 0.000 137.620 57.7 78.5 27.95 -0.13 1.789 9.311 27.034 0.000 137.640 57.7 78.5 27.93 0.01 1.790 9.315 26.948 0.000 137.660 57.6 78.4 27.92 0.15 1.791 9.318 26.858 0.000 137.680 57.6 78.4 27.91 0.29 1.792 9.322 26.763 0.000 137.700 57.6 78.4 27.89 0.43 1.793 9.326 26.664 0.000 137.720 57.6 78.3 27.88 0.56 1.794 9.330 26.561 0.000 137.740 57.6 78.3 27.86 0.70 1.795 9.333 26.455 0.000 137.760 57.6 78.3 27.85 0.84 1.796 9.337 26.345 0.000 137.780 57.6 78.2 27.84 0.98 1.797 9.341 26.233 0.000 137.800 57.5 78.2 27.82 1.12 1.799 9.345 26.118 0.000 137.820 57.5 78.1 27.81 1.26 1.800 9.348 26.000 0.000 137.840 57.5 78.1 27.79 1.40 1.801 9.352 25.881 0.000 137.860 57.5 78.1 27.78 1.55 1.803 9.356 25.760 0.000 137.880 57.5 78.0 27.76 1.69 1.804 9.360 25.637 0.000 137.900 57.5 78.0 27.74 1.83 1.806 9.364 25.512 0.000 137.920 57.4 77.9 27.73 1.97 1.807 9.367 25.387 0.000 137.940 57.4 77.9 27.71 2.11 1.809 9.371 25.260 0.000 137.960 57.4 77.9 27.70 2.25 1.811 9.375 25.133 0.000 137.980 57.4 77.8 27.68 2.39 1.812 9.379 25.005 0.000 138.000 57.4 77.8 27.66 2.54 1.814 9.383 24.876 0.000
This was mostly just an exercise, to understand how the software works. It’s kind of silly to use a linearly polarized antenna for the circularly polarized polar orbiting satellites (3db mismatch), but I’d still be interested in hearing any comments about this design from knowledgeable antenna design people.
I think this was the best ad during the Super Bowl (which actually for the first time I think eclipses the advertising spectacle that is the Super Bowl).
YouTube – FedEx 2008 Super Bowl Ad
It’s just that the weather has been too crappy for me to stand outside with my laptop and do the recordings. But today, the weather dawned nice, and so I did manage to record a nice western pass of NOAA17.
I heard on the amsat-bb mailing list that the repeater aboard the ISS might be active, so tonight I waited for a pass, which occurred at 8:10 or so UTC (just after midnight localtime). The uplink was around 437.800, the downlink on 145.800, which is sort of the reverse of the normal operation on AO-51 or the other easysats. Unfortunately, the pass was low, and to the north east, which is my least favorable horizon. In addition to the high horizon, there is a strong noise source in that general direction, strongly emitting on 145.825Mhz. Still, I put on some jeans and wandered outside for the pass.
I had some difficulty getting it at first: the high horizon wasn’t helping. But suddenly, I got some quieting, and could hear my voice (sounding slightly companded or something) booming back from the ISS with full quieting. I called CQ on the empty satellite a few times, and was just about to give up when I got KB9VSB, Dwight, from EN52 (nearly 3000km, and I think my first Wisconsin QSO). Sadly, I muffed the exchange, and just as quickly as I got the quieting, I lost it, probably as the satellite dropped below the peaks to the east. Rats.
I’ll be trying this again tomorrow.
Oh, I did record the pass too. It’s not very exciting, but here it is:
My first attempt at voice contact via the ISS FM repeater
Addendum: Tried it again too, and got Patrick, WD9EWK, and VE6EGN, Egan, from DO23. Heard some more people too, VE6GAV, AK5V, VE5ISS, and others… Got garbage at the end, the pass was pretty low.