RRBlog: Decoding NOAA APT Weather Images

[dchurch24]

Ok, well there has been some improvement - still grainy, but it's starting to look like what I'm after.

The only difference was that I raised the antenna back up again, as the signal became really weak when low down - which is wasn't when I first moved it.

I think I need to experiment with moving the antenna about to get the least interference.

 

[KE5MC]

Couple of bands near center look very good! Noise level changed from top to bottom, were you changing your setting or moving the antenna? If the setup was static, meaning no changes being made and it was a windy. That could point to antenna construction with the antenna moving.

Excellent improvement.

 

[dchurch24]

I actually had to go out this morning (to fix someone's computer for them - bloody Windows - Argggh!), and I set it off recording using WXtoIMG, so the whole things was static - it's not that windy today, and the sun is out.

As I wasn't here, the settings stayed the same throughtout the whole recording.

That image was taken using NOAA15, the attached one was from about 30 mins ago from NOAA18.

 

[dchurch24]

Oooh, oooh, oooh....Moved the antenna at a slight slant and the pictures are getting so much better.

A little bit more experimentation and I think we're getting there!

EDIT: there seems to be some sort of uniform interference as can be seen by the bands of noise at uniform intervals. I'm hoping it's not a pager - certain pagers are known to be transmitting on similar frequencies. I was hoping that no-one used these any more!

 

[KE5MC]

Found this while looking for information on you antenna construction.

During field testing I noticed that the QFH appears to have distinct directivity in relation to linearly polarised signals. In my case there is a pager transmitter, which makes reception of signals on 137.5 MHz almost impossible. This interference is not intermodulation and it is there when no signal is being received from the satellite. I found that by turning the antenna when not receiving a satellite signal, it was possible to find a very distinct reduction or sometimes a "null" in the strength of the interfering signal. This has enabled me, for the first time, to decode NOAA 12 signals on 137.50 MHz. A similar improvement could be obtained when dealing with other forms of linearly polarised interference.

I noticed looking at the inside picture of your antenna that it has an exposed connection at the top left in the picture from what I could tell. Coaxial cable will wick water down the center conductor and shield braid if not waterproofed from the elements. This will have an impact on how well it will receive the satellite. You may have addressed that before the antenna when outside, but I thought it was worth mentioning.

 

[dchurch24]

Hi, thanks. I did address the bare-wire issue before the antenna went outside - a coffee jar lid did the trick nicely!

I will continue to experiment with the position of the antenna and report the results, I have already moved it - it's closer to the building now, and oddly that provided the above image.

 

[dchurch24]

Well, they are certainly getting better.

I have experimented with antenna position, but I think this is as good as it's going to get for the moment.

Like I said earlier, I have some much better quality coax coming so the noise level will hopefully drop once I start using that - I won't have it for a week though, so will just carry on trying to find the optimum position for the antenna in the meantime.

 

[KE5MC]

best yet!

Until you try it, will it be less noise or more signal. You can see when the satellite is just above the horizon at the top and bottom of the picture it fades in at the top and out at the bottom. Much improved for when you 1st started.

My efforts, while not satellite have had little success. I realize that a better antenna setup is needed. One that is removed from the noise envelope of the electronic equipment. It might sound good to the ear, but the decoding program shows every flaw in the signal.

Mike

 

[dchurch24]

Well, it's not getting much better, but it's ok. I'm happy in any case ;-)

I am getting the new cable next week, so will try with that and post the results.

 

[yn0t]

Forgive me for raising a VERY old thread here... I was looking around online today and I realized that I never replied with my solution after asking all those questions earlier...

Here's what I was able to come up with...
Quadrifilar Helix Antenna (137 MHz) for NOAA Weather Satellites | Gregory Strike

As you'll be able to tell the Uniden BC780XLT was actually able to do quite well. I'm not certain it's that lack of bandwidth was an issue here.