Sound card considerations

WSPR signals are decoded by the PC which is running WSPR software. As such, as the old adage goes “rubbish in, rubbish out” is very pertinent when you get to this stage.

It was quite evident that my poor little receiver wasn’t getting anywhere near to what it was capable of. USB ports can be very noisy places and I had a sneaky suspicion that wasn’t helping matters in the slightest. By attaching a couple of ferrites to both ends of the 5V USB power cable and the audio cable, the dB indicator within WSPR was reduced slightly but the volume and quality of the spots didn’t increase dramatically. Stellar advise to get the Rx Noise dB level as close to 20 as possible.

Once again the set of cans and audio pass through we’re broken out and it wasn’t that impressive. To reduce the Rx Noise sufficiently so WSPR was happy meant having an input level just above zero. You don’t have to be very knowledgeable at all to work out that that isn’t optimal by any stretch.

Wise advice from Andy (G7UHN) was that PC sound cards utilising mic inputs will never produce anywhere near as good quality signal as a line-in input, but that’s where a lot of laptops fall down.

Firstly you don’t get a whole host of connectors, unlike a full size PC and secondly the embedded chipset of your laptop sound card is unlikely to give a sampling rate anywhere near what you need.

After a lot of googling, if you want to do this properly, you need to be spending serious money on a sound card that will give you good quality audio into the PC to allow it to do what’s needed and decode the spots.

If you’re running on a desktop PC and can accommodate a PCI card this comes highly recommended –

ASUS Xonar D1 7.1 Sound Card

http://www.asus.com/Sound_Cards_and_DigitaltoAnalog_Converters/Xonar_D1/

as does this

ESI Juli@

http://www.esi-audio.com/products/julia/

If you’re going to do it on a laptop or can’t accomodate a PCi card then this is where you need to be going

USB2SDR

http://www.wb5rvz.com/usb2sdr/

I’m looking towards using a Softrock SDR transceiver eventually and if you believe everything you read, you need to invest serious money to reap the benefits.

All of the above sample at 192kHz which gives you a much wider spectrum to play with. Think of it as a panoramic vista. You want frame-less sliding doors to enjoy the view from your living room, not a port hole!

That said I haven’t got that kind of cash to hand at the minute, plus I’m working in the here and now. After a week of dead ends and frustration I wanted this thing running now!

After a bit more googling I found that Creative Labs used to do a very nice USB sound card in the form of the Sound Blaster Live 24 USB.

http://www.amazon.com/70SB049000000-Creative-Technology-External-external/dp/B00030099O

It samples at 192kHz, just what’s needed. Now discontinued unfortunately, but eBay is everyone’s friend and for £20 I wasn’t complaining. It turned up yesterday.

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