Saturday NOAA 17 pass..

February 9, 2008 | Amateur Radio | By: Mark VandeWettering

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.

Feb 09, 2008, NOAA 17 on an 86 degree pass

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:

Interference pattern, recorded by Mike, WA7QPC

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. 🙂

Comments

Comment from Untung Suharto
Time 2/9/2008 at 4:10 pm

After read your email on yahoo group,I have advise you more better you use Helix antenna for wx apt receive from NOAA satellite.(helix antenna build myself) from junk yard.

my experience I use 2 wx apt radio receiver one from Hamtronics and the other from Miroslav Gola czeckoslovakia republic.

I can get nice picture after decode by wxtoimg software every day.

Comment from Jerry KD6JDJ
Time 3/18/2008 at 9:43 pm

Hi Mike Does your interference (as shown in the “gorgeous 86 degree pass” occur often? I was tempted to try to figure out what might cause that interference pattern. But, I soon realized that it it is too difficult for me. But, there is a relationship to something a little faster than 1 Hz. A sweep across both sides of the image takes about 1/2 second (I think). The noise seems to stop abruptly after about 1/8th of a second, but only on alternate sweeps. And, alternate sweeps are 1/2 second apart.
The fact that the interference brightens at the right side of the ‘noise’ line might indicate that there is a strong increase in signal strength at that time. Like a amplitude pulse thru a FM system.
Now, I too would like to know where that pattern comes from.
Jerry