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Author Topic: Damn Nice VLF SDR is Yours Free!  (Read 22514 times)
K0OD
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Posts: 2539




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« on: December 31, 2012, 09:13:43 AM »

Here's a remarkably good free radio:

I downloaded the files for the SAQrx receiver and they installed immediately on my computer. With my 192 kHz sound card I'm getting about a 100 kHz bottom slice of VLF. You'll only get about 45 kHz with more basic sound cards.

Run some kind of antenna (I used my 43' HF vertical) into the left mic input of your computer. Watch out for static on the wire if you're using a big longwire or the like. Disconnect large outdoor antennas when not in use.

What does this SDR look like?
https://sites.google.com/site/swljo30tb/_/rsrc/1349773059447/home/saqrxv09_screen.png

You can be listening to VLF within the hour.
http://dl1dbc.net/SAQ/

Digital stations that are especially loud in Missouri and their carrier frequencies:

  21.40 NPM Oahu HI (not 24/7 copy here)
  24.00 NAA Cutler ME
  24.80 NLK Jim Creek WA
  25.20 NML LaMour ND (very very loud 24/7)
  60.00 WWVB Ft Collins CO

Also this is a chance to play with a basic SDR if you've never done that.
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N0YXB
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Posts: 304




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« Reply #1 on: December 31, 2012, 12:29:08 PM »

Interesting, thanks for posting this.
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Vince
SV1XV
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Posts: 93


WWW

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« Reply #2 on: December 31, 2012, 10:51:00 PM »

I use it with my laptop for frequencies up to 22 kHz. However I have built a small two transistor front end so I can use an antenna of reasonable size. Visit the following pages for details.


HNY DE SV1XV
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KE5JPP
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Posts: 0




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« Reply #3 on: January 04, 2013, 09:07:47 AM »

After staring at the lines in the waterfall for a few minutes and looking at the blips from WWVB, it is DAMN boring.

Gene
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K0OD
Member

Posts: 2539




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« Reply #4 on: January 04, 2013, 10:43:07 AM »

I thought you were going to complain about using a sound card or perhaps the SAQrx price, Gene.

--
ELF propagation is slightly interesting. I was actually keeping records of signal strength of some stations for a few days. Amazing that a sound card with a hunk of wire for an antenna  can pick up stations (high power ones, certainly) from 7,000 miles away or more.  

Higher up, the ham stuff around 475 kHz is interesting during winter when there's not much else going on. All sorts of modes are used, from QRSS to sideband. You'll see international Qs when that's permitted by the FCC, probably soon.

I just got a Palomar converter for use with my Flex-5000. Curious to compare it to that free SAQrx sound card receiver in the ELF range.
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KE5JPP
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Posts: 0




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« Reply #5 on: January 04, 2013, 11:14:57 AM »

I thought you were going to complain about using a sound card or perhaps the SAQrx price, Gene.

--
ELF propagation is slightly interesting. I was actually keeping records of signal strength of some stations for a few days. Amazing that a sound card with a hunk of wire for an antenna  can pick up stations (high power ones, certainly) from 7,000 miles away or more.  

Higher up, the ham stuff around 475 kHz is interesting during winter when there's not much else going on. All sorts of modes are used, from QRSS to sideband. You'll see international Qs when that's permitted by the FCC, probably soon.

I just got a Palomar converter for use with my Flex-5000. Curious to compare it to that free SAQrx sound card receiver in the ELF range.

I am not complaining at all.  ELF and VLF is very interesting to me, but it will not be very interesting to the majority of Hams who are just wanting to try out SDR.  If you are interested in SIDs, Sprites, Whistlers, 'Natural Radio', AGO, 'Sferics, Tweats, 'chorus', and such, you might find this interesting.  You can't see much higher than about 90 kHz with a 192 kHz sound card, depending on the sound card and where the anti-alias filter rolls off, so ELF and VLF is it.

Online VLF receiver: http://www.spaceweather.com/glossary/inspire.html

Gene
« Last Edit: January 04, 2013, 11:18:52 AM by KE5JPP » Logged
SV1XV
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Posts: 93


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« Reply #6 on: January 05, 2013, 07:54:39 AM »

See also this presentation: A front end for a Software VLF Receiver in the Lowdown, September 2011.

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K0OD
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Posts: 2539




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« Reply #7 on: January 05, 2013, 08:42:13 AM »

With my sound card, SAQrx goes up to about 97 kHz. Not bad for free. Lesser sound cards will only get you about 22 kHz.

I've been struggling for a while to hear ANYTHING below 530 kHz on my 5000. The LYQ  beacon on 529, comes in fine, but below that there's nothing but ghosts of BCB AM including some stations hundreds of miles away. My new Palomar converter does the trick in getting the Flex to work down to well under 10 kHz.

I was also told that the tiny Jackson Harbor converter kit works great for few bucks it costs.
http://www.eham.net/reviews/detail/5270
http://wb9kzy.com/lfconv.htm

Those natural sounds don't interest me. Latest project is to track down local hash that sometimes plays havoc with my VLF reception. Last night the range from 200-400 KHz was covered with noise from outside the house for a few hours. The Flex NB took out much of it. I'm keeping a log of noise levels starting today.  Should be fun to figure it out.  
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W8AAZ
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Posts: 333




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« Reply #8 on: February 08, 2013, 11:21:28 AM »

Hmm. You know, it seems that listening below 100k is easy enough, hearing something is a different matter.  However.  I was just thinking about that range.  Then I remembered that the second IF frequency of my Drake SPR 4 receiver is only 50 KHz.  So now, perhaps there is some way to make use of the sound card and all the fancy DSP and tricks to make a vintage radio do amazing stuff?  Couple the output of the second IF into the sound card, and then perhaps the limits of possibilities are determined by the software available?  At practically no cost if  you have a Drake and a computer or laptop?  Tell me if I am blowing smoke?
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K5TED
Member

Posts: 703




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« Reply #9 on: February 08, 2013, 08:55:07 PM »

Hmm. You know, it seems that listening below 100k is easy enough, hearing something is a different matter.  However.  I was just thinking about that range.  Then I remembered that the second IF frequency of my Drake SPR 4 receiver is only 50 KHz.  So now, perhaps there is some way to make use of the sound card and all the fancy DSP and tricks to make a vintage radio do amazing stuff?  Couple the output of the second IF into the sound card, and then perhaps the limits of possibilities are determined by the software available?  At practically no cost if  you have a Drake and a computer or laptop?  Tell me if I am blowing smoke?

Do It!
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K5TED
Member

Posts: 703




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« Reply #10 on: February 08, 2013, 08:58:53 PM »

BTW, I connected a 40' wire through a 9:1 balun to the microphone input on my PC. The onboard sound can do 192kHz sampling, so I got a nice range on the SAQrx. WWV was there, no problem, didn't see much else.
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N8CBX
Member

Posts: 141




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« Reply #11 on: February 10, 2013, 04:20:11 PM »

Could one use electrical power lines as an antenna (doing it somehow in a very safe manner?). I remember my first cordless telephone (1.8 Mhz I think) used the house electrical wiring as the antenna.
Jan N8CBX
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