Weather Satellite Receiving Station


16 posts
by denhamflyer » Fri Jan 27, 2012 2:20 pm
I'd love to build a weather satellite receiver station, just need a basic receiver connected to the audio input of the R-Pi which can then do the audio signal processing to generate the images.

I think that this would also be an ideal project for a classroom as receiving and displaying live images from space of earth would be pretty interesting to most kids.

I've been looking at the various software out there today and it is all windows based, can't see any Linux binaries for this application. Anybody know of one?

Cheers,

Colin
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by error404 » Fri Jan 27, 2012 6:31 pm
http://www.wxtoimg.com/ Though it is not open-source, there are Linux builds and you might convince the author to build it against ARM for you.

Also, with sources:

http://atpdec.sourceforge.net/index.html

http://5b4az.chronos.org.uk/pa.....s/apt.html
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by denhamflyer » Sat Jan 28, 2012 9:34 am
Thanks for that, I'll check it out!!

Cheers,

Colin
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by kme » Sat Jan 28, 2012 9:36 am
There is no audio input.
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by roelfrenkema » Sat Jan 28, 2012 10:07 am
Not on board but as the faq states an usb sound device is supported.
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by kme » Sat Jan 28, 2012 10:29 am
roelfrenkema said:


Not on board but as the faq states an usb sound device is supported.


Oh right, forgot about that.
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by hpux735 » Mon Mar 26, 2012 3:49 am
denhamflyer said:


I'd love to build a weather satellite receiver station, just need a basic receiver connected to the audio input of the R-Pi which can then do the audio signal processing to generate the images.

I think that this would also be an ideal project for a classroom as receiving and displaying live images from space of earth would be pretty interesting to most kids.

I've been looking at the various software out there today and it is all windows based, can't see any Linux binaries for this application. Anybody know of one?

Cheers,

Colin


I think that's a great project idea.  I've experimented with this myself, and had a great time. Receiving weather satellite images with Softrock I did mine with a "Software defined radio," which would be a great next step once you try it with another radio.  General purpose communication receivers don't have enough bandwidth to properly receive weather satellite images, but it will still work.  It will probably look fairly nasty.

Another aspect of the project that might be fun with the kids is building a special antenna for receiving the satellite signals.  Helical Quad Antenna for Weather Satellites
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by en4rab » Sat Apr 07, 2012 9:21 pm
If you are interested in radio applications then you might wish to have a look at this: http://sdr.osmocom.org/trac/wiki/rtl-sdr

I very cheap USB dvb-t receiver that can be used as a software defined radio with GNU radio.

The chinese makers have cottoned on really quickly and upped the prices on ebay for ones that definately work by about a fiver but its still great value:

http://www.ebay.co.uk/sch/i.ht.....w=RTL2832U
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by PaulTech » Sun May 06, 2012 9:42 pm
I have seen in another post someone has made a driver for the RTL on RPi, really even using two RPis(one receive,one processing) and a RTL SDR would still be cheaper than most 137MHz receivers.
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by Dave_G_2 » Thu May 10, 2012 6:13 am
hpux735 said:


General purpose communication receivers don't have enough bandwidth to properly receive weather satellite images, but it will still work.  It will probably look fairly nasty.



From what I understand, the data on 137Mhz is frequency modulated, so why not make a downconverter and use a FM radio to do the demodulation.

The standard bandwidth of a FM radio demod  is around 75KHz.

The converter can be preceded by a 137MHz bandpass filter and a low noise amplifier before being mixed with 37Mhz from a crystal controlled local oscillator which would give 100MHz out after some more filtering.

Since a standard FM radio has a tuning range of 88 – 108 MHz, a third overtone crystal for the local oscillator can be chosen so the the weather sat data will be available on an unused part of the FM band.

Then it's a simple matter to work backwards and select a crystal with the correct frequency.

There are plenty of 3rd overtone crystals available in the required range (29MHz to 49MHz).

EDIT:

Car radios are great for this kind of thing as they are fairly cheap, widely available, are synthesized and have pretty good sensitivity.

They also have a proper RF input (closer to 90 ohms then 50 ohms).

Just get a basic model with no fancy RDS features and no high power output as this will only complicate power supply requirements.

An added bonus of many car radios is that they also have a line level audio output which can be fed to a sound card whilst the speaker outputs can be used to "listen" to the signal via a speaker or a pair of headphones.

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by Dave_G_2 » Thu May 10, 2012 6:58 am
For the front end filter, a helical type filter could be used as they are pretty simple to tune and offer good selectivity versus number of stages.

Just keep the insertion loss down or this will degrade the overall noise figure.

See below:

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by Dave_G_2 » Thu May 10, 2012 9:47 am
Sorry I can't work out how to edit a post to contain more then two pics in sequence.

Anyhow, below is a schematic for a possible converter using the NE/SA602 IC and a dual gate mosfet as a LNA.

(I modified it from the NXP datasheet which can be found here: http://www.nxp.com/documents/d.....SA602A.pdf).

I haven't tried it but may do so when time permits.

Quite interested in receiving the weather maps/pics myself.

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by PaulTech » Mon May 14, 2012 6:33 pm
The main reason the FM broadcast receivers don't work is noise. The WX is 25KHz wide and FM is 125KHz wide. I wish you could simply up-convert, it would have saved me a lot of time & money building WX sat receivers. Playing with RTLs now, and will soon have one on WX duties. I would definately like to try a RPi as the receiver, using a RTL but probably won't be sent a RPi til next year.
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by Dave_G_2 » Mon May 14, 2012 7:34 pm
Keep in mind that we have to add extra for Doppler shift so a bandwidth closer to 40 or 50KHz is what would be required.
The extra bandwidth of the FM receiver shouldn't be a problem if the noise figure of the receive system
is kept low and we have sufficient gain by using a good antenna system and LNA.

I'm also waiting for my Pi but in the meantime I think I will build some "turnstile" dipoles from some
aluminum tubing housed in some PVC tubing.
Have found some low noise GaAsFets made by HP so will probably make a LNA from one of those and try out the FM convertor idea feeding the audio output to a XP box I have here.

If the results are not that great then I reckon I'll have a go at replacing the FM receivers I.F. SAW filters
with one of these:
http://parts.digikey.com/1/parts/403992 ... 7-30a.html
It may need some simple matching to bring the impedance closer to the "cheaper" ceramic type SAW
filters found in FM receivers.
Still much easier and cheaper then buying or building a dedicated receiver.
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by Dave_G_2 » Mon May 14, 2012 8:46 pm
Did a "quick and dirty" simulation to see what it would take to match the xtal filter with an impedance
of 5k ohm and about 0.5pF to a ceramic filter which have an impedance of around 330 ohms
in parallel with 10pF.
It shows an expected loss of around 12dB which could easily be overcome with a single stage of amplification.
Image
http://s16.postimage.org/yph2pr9bp/IF_FILT_SIM_1.jpg
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by yv1hx » Thu Aug 30, 2012 3:46 pm
Please have a look to this site: http://www.df2fq.de/english_version/r2fx_eng.html, maybe is a bit expensive, but may be worth the effort.
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