Monthly Archives: December 2007

Another weather satellite pass…

Well, during a road trip with my wife to San Diego and back, I managed to begin to type up my notes for an upcoming tutorial article (cross fingers) on reception and decoding of weather satellite imagery. I basically reimplemented what I had, stripping it down to its barest essence, and trying to make it easy to understand, yet still capable of creating good imagery. Oddly enough though, in the process, I inadvertently seemed to introduce some aliasing artifacts which I must admit, are puzzling me mightily. Oh well.

This morning I decided to try to record a low 25 degree maximum pass of NOAA17 that occurred to the east. It starts out fairly noisy because I have a pretty high horizon to the northeast. The first is my “advanced” decoder, which is about six times longer than the simpler decoder I wrote.

My “advanced” decode…

The second is the same data file, processed with my “simple”, easy-to-follow decoder. The only serious feature it is lacking is the sync detection and rectification, which as soon as I can figure the simplest way to add, I’ll try to get in. The simple version is two pages of code, not including the data for the filter tables.

My “simple” decode

Fixed a few bugs…

I got some time today waiting for the furnace guys to show up (they never did) and managed to figure out a few of the things that were wrong with the image normalization code and with the sync detection code. Here’s the latest automatically generated image from one of the recordings I made earlier.

Satellite Image

There are a couple of things about these images which aren’t precisely correct, but overall the rectification works pretty well: the sync detection is working and reasonably reliable in the regions where the image is essentially nose free. With some additional work, I could be even better, and the occasional one pixel glitches in the position of the scanline would likely go away. The normalization isn’t perfect either. But still… pretty neat.

How not to watch The Incredibles

Okay, I admit it. I have a special place in my heart for The Incredibles. It was my first opportunity to work for Brad Bird. I worked with a lot of really great people, many of whom I went on to work with again during Ratatouille, and let’s face it: I just love the whole comic book/superhero genre.

It’s hard to describe what I spend a lot of my time doing during movie production, but I’m often working in the rendering department. It’s our responsibility to make sure that each and every frame of each and every shot meets with the directors approval. We fix all sorts of minor technical issues, and even the occasional odd bit of animation or lighting. When the shot clears out department, the director has basically said that he’s approved the look of the film (minor changes can be made in image mastering, but hopefully they are minor).

That’s why it’s so painful to watch The Incredibles on the ABC Family Channel on Comcast.

To be honest, I don’t know whether it’s the Family Channel’s fault or Comcast fault, but sweet spirit of camphor, are they sending the movie down the pipe at 500kbps or something? The transfer is simply awful. Dreadful. Unwatchable. Words escape me how terrible it is. Pixelation. Colors are crushed. Mosquito noise. It’s just pathetic.

Please, please, please. Watch the DVD. It’s really quite good. Don’t judge it by the youtube experience you see on the Family Channel. I’ve seen better from pirate DVDs from Singapore.

Sorry, just had to get that off my chest.

Merry Christmas to all BrainWagon readers

I’m sitting up in bed, laptop buzzing away, with my wife sleeping next to me. Within the next hour, we’ll have showers taken, coffee brewing, and begin opening presents. I didn’t get the house cleaned as much as I would like and my wife’s Jeep still needs its wiper arm replaced (did they Loc-Tite the bolt or what?), but for today, the sun is shining, there are presents under the tree, and all is well with the world.

Best wishes from me and mine to all of you and yours. Merry Christmas.

You can hear Genesat telemetry too…

Okay, I was bored waiting for potential Ande passes, so I tuned into Genesat. I got a few telemetry packets, although the frequency seemed to be 5khz low from the published frequency of 437.075Mhz.

KE7EGC>UNDEF,TELEM:GeneSat1.orgB4511B0A00000000000000260069009F7113722166CC790B02F0
KE7EGC>UNDEF,TELEM:GeneSat1.orgFA511B06000000000001002600690001EA02BA27081CBF026621
KE7EGC>UNDEF,TELEM:GeneSat1.org04521B8A010E018901DD010100A4015F2DCB1C226D951D1C023A
KE7EGC>UNDEF,TELEM:GeneSat1.org36521B73010F017101DE010000A4019F992216023D996D22E207
KE7EGC>UNDEF,TELEM:GeneSat1.org3B521B72010F016E01DE010000A4015F2DCB1C226D951D1C023A
KE7EGC>UNDEF,TELEM:GeneSat1.org40521B0100000001000100250069005F2299221C02202274231C
KE7EGC>UNDEF,TELEM:GeneSat1.org45521B0200000002000000260069009F07BC13A0230013281C02

Not sure what any of it means, but there it goes.

Ande Still Lives at 21:53Z

Around 21:53Z, I got two packets for the NO-61, otherwise known as ANDE

ANDE-1>BEACON:T#002,002,010,009,004,003,01000000,000
ANDE-1>APRS2,SGATE::BLN2ANDE :ANDE stays  awake for 30 secs after last pkt heard.

Ande is due to deorbit very soon, probably within the next 24 hours, maybe even sooner. My orbital elements indicated its altitude was only about 107 miles, and it’s dropping fast. I won’t likely get another good chance to here it. Merry Christmas Ande, and thanks from all the radio amateurs whom you have helped entertain and educate.

Addendum: The software I use for satellite predictions no longer predicts any passes for Ande. Sayonara.

NO-61 has decayed, at least according to “predict”
Addendum2: Predict is no longer guessing where ANDE is: it merely marks the position as “decayed”.

SO-50 pass this morning…

During the SO-50 pass this morning, WA8SME was asking if I was using a preamp, and whether I had any difficulty with receive sensitivity. On the Amsat mailing list, I’m amazed by reports of people who get weak signal strength using 14 element antennsas and the like, my handheld Arrow antenna, while not perfect, is remarkably good, and I normally hear just about everything on the satellite.

Here’s a link to the mp3 as recorded on my Sony voice recorder:

SO-50 pass, with QSOs from WA8SME, N6KTH and W6HF (with a brief appearance from AB9LA)

Google Maps can find you without a GPS

Google Maps for mobile phones apparently has a new feature that enables you to automatically determine your position by triangulating your location from cell towers (much like the Navizon client does). This is very cool! Unfortunately, you can’t update the google maps application on the iphone, so I can’t tell how well it works. Are you listening Apple? Get it on the iphone soon.

Tonight’s AO-51 pass…

I managed to work WD9EWK from my car using only my Kenwood HT and the omnidirectional whip mounted on the roof of my SUV. I didn’t have my voice recorder with me, so I didn’t get a recording though. Obviously using an omni antenna picks up a lot of signals and intermodulation distortion: there were all sorts of carriers and pager noise from all directions. Still, it was doable. QRP into an omni!

Narrow versus Wide FM

While discussing my experiments with weather satellite reception, I talked about how I made my recordings using the “WFM” or wide FM settings on my Radio Shack Pro 60 scanner. If you read up on this subject, you’ll find that the signals transmitted by these satellites have about a 50khz bandwidth. The normal “narrow” FM mode used by most HTs and scanners have about 15khz bandwidth. The wide FM settings have 200khz bandwidth. If you record a signal this way, you are about 6db down, and you have the potential to capture strong signals which would normally be out of band, but if it works, it works pretty well. But someone asked me “What happens if you record with the normal 15khz setting?”

So I did the experiment.

Narrow Versus Wide FM

The first bit of this run was recorded in the narrow setting. The majority was recorded in the wide setting. These were done using my VX-3R, which was handier than my Pro60. If you look at the top, you can see that the results are noisy, and we get no darks. If I thought really hard about this, I probably could tell you why this happens, but that’s what you get.

Addendum: I worked a bit on the image, cropped out the noisy bit, and adjusted the balance and color a bit. This is what you get.

GIMP’ed version of the same picture, cropped, rectified.

Chatting on AO-51

It was positively chatty on the westward pass of AO-51 this morning. For fun, I reduced power to just 1w on my HT, and nobody seemed to notice, although it did get scratchy at the end of the pass.

Dec 16 pass of AO-51, 8:57 Local Time

The beginning of the pass is a little noisy, because for some reason I thought the pass was going to the east, when it was in fact a western pass. I was fishing around with the antenna, trying to track it to the east. Once I realize how stupid I was, it settles in to a fairly strong signal.