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Newb trying to receive Weather Faxes

Posted: Sat Aug 10, 2019 8:41 pm
by Dingus
Hi all,

I'm a complete newbie to SDR, but I've managed to get the RTL-SDR dongle working with my Mac and using the GQRX software to tune in local FM radio stations and AM air traffic communications. <whew>

With that said, I have ZERO radio experience - this is me just dipping my toe into it. The main driver for me to get started was an interest in receiving Weather Fax information at sea.

I've just come to understand that the dongle I have will work down to 24MHz and the information I found on the stations that broadcast weather fax data is as follows:

"The only requirements of the radio are that it tunes the frequency ranges of interest. A general purpose communications receiver tuning 0-30 MHz is ideal, SSB marine radios may also be used, if they can receive the frequency bands of interest. The radio must be able to tune in USB (upper sideband) mode. Inexpensive portable radios are not as satisfactory, although higher-end units can work well. The radio must be able to tune in small steps (10 Hz), or have some sort of a fine tune adjustment."

So...it seems that the dongle I have won't work as-is? Do I need an "upconverter"? (I don't really know what that is but have seen that term used in some of my research).

If anyone would share any tips for getting Weather Fax info onto a Mac, it would be very much appreciated.

Thank you and cheers!

-Dingus

Re: Newb trying to receive Weather Faxes

Posted: Sun Aug 11, 2019 3:24 am
by rjmura
i don't have a mac, but you may be able to figure out how to do it by seeing how i do it on a pc.

1. you can tune your sdr below 28 MHz by direct sampling the Q branch. on sdr sharp, this means changing the sampling mode from quadrature sampling in the configure source menu.
2. go to https://www.nws.noaa.gov/om/marine/radiofax.htm to find noaa stations in your area. tune to a station 1.9KHz below the frequency listed, in USB mode. you'll need a short wave antenna. in my case, the only station i receive consistently is at 11.0881 MHz, and only in the evenings. so you may have to try various frequencies at various times.
3. get a copy of VB virtual audio cable to pipe the audio from your sdr radio to fldigi. vb virtual audio cable is a must because it is used for so many other applications, e.g., receiving noaa weather pictures.
4. get a copy of FLDIGI (i think there is a mac version). there are many youtube videos on how to use fldigi.
5. in fldigi, choose the WEFAX 576 mode, and set the volume on your sdr radio to get a yellow signal on a blue background in the waterfall. place your cursor at the middle of the signal and click. (turn off AFC). you'll have to read the fldigi instructions to learn all the fine points.

good luck!

Re: Newb trying to receive Weather Faxes

Posted: Sun Aug 11, 2019 6:23 pm
by Dingus
Thank you for your reply. I understand steps 3-5, but completely clueless on everything contained in steps 1-2. It sounds like there's a lot of good information in there, I just don't know how to make sense of it! LOL

It seems, however, that Step 0 for me is to get a short wave antenna?

I found some information (but have no idea if it's true) that I can just use about 40 feet of Coaxial cable?

What would you suggest that I use for an antenna for this application? Keep in mind that the final implementation will be to have this setup on a sailboat.

Thanks again for the help and patience!

Dingus

Re: Newb trying to receive Weather Faxes

Posted: Mon Aug 12, 2019 2:45 am
by rjmura
what program (e.g., sdr#, sdr console, hdsdr, sdruno) are you using for your radio?

for step 1, when you run your sdr radio, look for a configuration menu (like a gear) that shows "quadrature sampling". if you click on the drop-down box, you should see something like "q branch".

step 2 is the noaa website for weather fax. depending on where you are, you need to find a shortwave station that is broadcasting wefax, and which you can receive. the frequencies listed are somewhat confusing because you need to set your frequency 1.9 kHz lower than the listed frequency, as explained on the website. you also need to set the mode on your sdr radio to USB (upper sideband). once you're able to receive shortwave stations, all the above should make sense.

as far as the shortwave antenna, i'm using a random piece of wire about 50' long, fed by a nooelec balun. if you're on a boat, ask other boat owners what kind of antenna they use.

Re: Newb trying to receive Weather Faxes

Posted: Tue Aug 13, 2019 12:34 am
by Kenn
I wrote an article about wefax awhile back that might help:

https://ranous.wordpress.com/2015/07/03 ... ax-charts/


It's based on using a shortwave radio. It can be done with an RTL dongle, but a good SW receiver performs better when the signal is weak.


The antenna system is very important as we need a reasonably strong and steady signal if we're to get readable charts. I'm in Arizona, well inland and far from any wefax transmitters but I can get decent signal with a 36' dipole. It has traps and is designed for the ham bands, so for wefax freqs it's really just a length of wire. I use an antenna tuner to peak the signal.

I don't know what antennas are ideal for sailboats. If the mast is metal I'd suspect that would work rather well, especially with a tuner.




-Ken