Thursday, May 28, 2015

Receiving and Decoding WeFAX (Weather Facsimile) Transmissions

Another "new" project popped up yesterday on the Iowa during our monthly Radio Guys meeting. Our guy who's rebuilding the CEC (Combat Engaement Center for the civvies) brought up the fact that eventually the Meterology Office on the Bridge Deck will be included on the tour route, and wouldn't it be nice to have a working weather fax on display.

This came up because I was explaining the PC, interface, and software I installed for the Amateur Radio Group to use, and showing how it's used to decode "digital" transmissions.

The most popular digital mode on the Ham bands is called PSK31, and is a narrow-band method of sending text, so you can have a keyboard-to-keyboard chat with another Ham.

The software I like to use is call "FLDIGI", and runs on Linux, Mac, and Windows. The nice thing about it is that it comes with software modems to decode literally DOZENS of digital transmissions.

There's nothing showing in the screenshot below as I don't have a radio hooked up to my Linux box right now, but I've mentioned FLDIGI before in other posts.



Here's a Windoze screenshot of FLDIGI receiving a weather report. The Signal-to-Noise ratio of this frequency is worse than the weather map, which explains the "snowy" image, and lack of correct side-to-side sync. This can be corrected in the program after the broadcast is recorded.


 
For a webapge giving the "Sights-and-Sounds" of the digital modes, head on over here. There are many other digital modes used, and this is just a small sample of them.

SO.....after the meeting yesterday, I looked up some wefax frequencies, and tuned in the Pt. Reyes Station Coast Guard broadcast, and tried to decode it. I'm not sure what was wrong, but we weren't able to decode an image. Since I've never tried that mode before, I suspect it might be operator error, and left it at that.

This morning I fired up my Windoze PC and my Flex 5000, and tuned in the same station. To my surprise, and using the defaults in the program, I was able to receive the image shown below.


This has me scratching my head, so I'll have to spend some time on the Iowa by meyself to see what's not configured correctly.

8 comments:

  1. Be sure to do a follow up with what you find. WEFAX on FLDIGI works fine for me with the TS-480 like it did for you at home.

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    1. WELL....since I made this post, I was tuning around a bit more, and landed on the same frequency we used yesterday.

      The spectrum looked the same, and I had a good S/N ratio, but got the same "blank page" we were receiving yesterday!

      I think the time and frequency we paicked at random yesterday was a period when they don't send anything. Maybe they use it like the RTTY guys do with their "idling" and just sending RYRYRYRY.

      If it's transmitting, and sending blank pages, it would at least allow the AFC on the receiving stations to maintain lock.

      Or maybe I don't really know how the system works!

      Anyway.....I'm heading in by myself tomorrow to experiment a bit more.

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    2. Wasn't able to get back there Friday, so this will ahve to wait until Wednesday.....

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  2. Sounds like a good project... And one that WILL enhance the tour! ;-)

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  3. There's an R-1051 receiver already in the Met Office, and we can patch it to any receive antenna on the ship.

    I scrounged up enough stuff to build a little Linux box, but we're deciding what to use for a display device. The printer that was there is gone, and besides, we don't want tons of scrolling thermal paper in there!

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  4. You probably have this, but just in case:
    http://www.nws.noaa.gov/om/marine/rfax.pdf

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    1. Yeah, found that one last week when I started experimenting with the wefax mode in fldigi, and didn't know any frequencise or the schedule.

      Thanks, though. I'll be down there again on Wednesday and see if I have any better luck. We'd like to have a little system ready-to-go for when they finish the Meterology Office. We still don't know if the R-1051 receiver in there works, and what we'll use for a display, but we'll get it figured out.

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  5. I found a sampl rate mismatch between Windoze and fldigi. I corrected it, and we're getting wefax pix now.

    Never had this problem on my home station becuase the "audio" from the Flex to fldigi is never analog....it's digital from the Flex receiver right into the program.

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Keep it civil, please....