Using RTL-SDR to decode EMWIN weather info

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cschulz
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Joined: Fri Mar 07, 2014 6:09 am

Using RTL-SDR to decode EMWIN weather info

Post by cschulz » Fri Mar 07, 2014 6:47 am

All,

I have been thinking about using an usb RTL-SDR to receive and decode the US National Weather Service EMWIN data stream.
This is a data stream publicly available to anyone with the appropriate receiving system.

I have a system running using a dedicated receiver (Werner Labs) which runs well but want to set up a system with a cheaper receiver for use in situations where the users may not be able to afford the expensive commercial systems. We are particularly interested receiving in Hurricane and tsunami warnings for the Pacific Islands. A number of locations use the commercial version but many more could benefit if the overall costs were lower. The dedicated I-Q receiver is the most costly item by far. > $US 900

The existing setup uses a standard PC sound card to digitize the I-Q output from the dedicated receiver set to 139.200 MHz IF output from a satellite downconverter operating at 1692.700 MHz. I realize that the RTL_SDR dongles will receive 1692.7 directly and would probably use this but here I already have the 139 MHz signal available feeding another higher data rate receiver for satellite imagery.

The data rate for EMWIN is 19.2 kbs with a bandwidth of around +- 30 Khz.

The decode software needs an I-Q input

The problem that I see is getting the I-Q data from a USB RTL-SDR module into the software.

I have both the Funcube dongle Pro and a couple of USB DVB-S modules to play with.

The data stream modulation is QPSK so the FM demod is of no use. It is possible to set the software for input on a particular port so it should be possible to use this combination but I am not far enough advanced with SDR theory to sort it out. The decode software can handle all the decoding from an I-Q input.

As the decode and display software runs on Win Xp / 7 only it is preferable to have a WIN solution.

I have full documentation for the existing receiver that works as well as the software so happy to supply that to anyone interested in this project.

I did note someone posted a similar query to another forum but as far as I know had no answers.

So if someone has some ideas I would be really appreciative of any suggestions / help. Sorry for long post but need to get basic info included. Many thanks in advance

regards

Colin Schulz
Pacific Island Meteorological Project.
(Comms Engineer).





There is a wealth of information on the broadcast

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