02/03/2011

Just what the Hell is flying around over my head?

Weather Satellite Update

I finally got a few moments of time to get everything together that I need to receive weather faxes from the old NOAA APT satellites. When I dusted off my Icom PCR-100 I noticed that the antenna connector was loose and a screw was missing for the grounding connection. So I needed to touch things up a bit before I could have this radio back in service.

When I popped the unit open I noticed that the connector was not only loose but was actually separated from the board. This would explain its lack of performance in the past. I removed the old connector and installed a new one and also took the liberty of installing a grounding lug coming out the back of the radio.

Here is the basic setup. I tried to minimize the noise and ground everything properly. There is a ground wire going to the newly installed lug. The antenna connector is attached to my antenna switch which offers my dual band quarter wave ground plan antenna to the radio. The speaker output is running through my signal link interface going to the computer’s sound input. The serial cable has two ferrite chokes to keep the noise down.

On the computer side of things, I use Adobe Audition to record the incoming signal. The fax software I have allows you to open a WAV file and process it to get a picture. This gives me the ability to clean up the WAV file a bit before I process it to reduce the amount of static and noise in the picture. The WAV file needs to be recording in mono and with a sampling rate of 11.025Khz.

My first attempt to decode the image was an exercise in fumbling with the controls. I was under the impression that this was a wide FM signal. So throughout the pass I was changing reception modes and playing with signal levels. Also the pass at 3:08PM was only a few degrees above the horizon so the signal was weak. Above is the result. You can sort of make out some cloud formations as I have pointed out. As the signal faded in and out you could see that the sync signal was lost and picture went out of skew. It’s not much of a picture but I did work out some kinks in the setup. I found the correct mode, narrowband FM with a 50Khz bandwidth, and also worked out the correct volume level going into the soundcard. Luckily there was another pass overhead at 4:48PM and the satellite would be farther over the horizon.

Although still dark, this result was a lot better. Jersey had quite a bit of haze and cloud cover on 02/02/2011, but I was able to make out the New York city area and a piece of New Jersey in this photo. There was still a lot of noise and the fading from the satellite racing overhead at 17,000 MPH. I ran the WAV file through a few noise reduction algorithms and then clipped off the high-end with a graphic EQ. I’m hoping that a nice sunny day will provide better results with lower noise and more features that are recognizable. A small clip of the sound file from this pass is available here. There is another pass of NOAA-15 at 4:23PM today where it will be 59 degrees above the WSW horizon. Hopefully I can get a better picture from this run.

Earlier this morning I noticed that NOAA-17 was going to fly overhead at 8:55AM and it would be 83 degrees over the horizon. That’s almost directly overhead! I couldn’t pass up this opportunity. The website said that this is the backup satellite for NOAA-15, so I figured I would give this one a shot as well. I tuned my radio to 137.500MHz, this is the satellite’s APT frequency. I noticed that when I tuned to this, there appeared to be a dead carrier keeping the static very low. It seemed like something was using this frequency but I figured that the satellite would overpower the signal when it flew overhead. The satellite kicks out a 5 watt signal which is pretty bright as far as satellites go. DTV satellites use 10 watts, to give you a comparison. I began recording at around 8:45am. As soon as the satellite signal could be copied It seemed as if something was wrong. A small sound clip can be found here. It sounds nothing like the NOAA-15 satellite and if you listen closely you can hear that the sync signal is drifting all over the place. There is no way I would ever be able to get a picture out of that. I’m still not convinced that the satellite is malfunctioning so much as I think that it could be some sort of weird intermodulation distortion problem from the other dead carrier I witnessed. I’ll have to keep playing with this one to see if anything will come of it.

As it stands right now I have another good pass of NOAA-15 at 4:23PM today and hope to get a good sunny picture out of it.

Updates to come.