Ross Primrose wrote: > > > The SignalLink USB is just a $20 USB sound card with a VOX circuit added > anyway.... See W4TV's post titled "Re: [Elecraft] AFSK - K3 - SignaLink > USB" from 01JUL10.... > >
I have just spent most of the day trying to set up one of my other radios to receive HF APRS on 300baud packet using a "$20 USB sound card" and the AGW Packet Engine soundcard modem. I had my K3 connected to the PC internal sound card and my FT-817 connected to the $20 USB card. I actually tried two USB devices. One was a real cheapie, more like $10. The other should have been quite high performance as it quotes a 48kHz sample rate and has two SP-DIF sockets on the front in addition to the usual array of speaker outputs. All of the packets copied were received by the K3 / internal soundcard. None were copied using the USB soundcard. To make sure it wasn't the radio causing the difference I swapped the audio cables over so the K3 was feeding the cheap soundcard and the FT-817 the internal one. All the packets copied then came from the FT-817. It was curious as I set up both radios / soundcards with simultaneously running copies of Fldigi. The waterfalls looked identical and PSK31 and PSK63 were copied using both setups. But 300baud packet using the AGWPE was a complete dead loss. I think there are various factors that could be at work here. I'm sure there are people more knowledgeable than me on this reflector so I stand to be corrected but I think it's possible that USB sound cards work at a fixed sample rate and perform resampling in the drivers which may result in the loss of information critical to decoding. Internal sound cards actually sample at the rate selected by the software. So USB sound cards may work fine with some less critical modes or with applications that use the same sample rate as the sound card, but with others they perform poorly. Therefore I think internal sound cards are always going to perform better, though the difference may only be noticeable with critical modes. Unfortunately they are getting expensive as bog standard sound cards are now obsolete, so you have to pay for a lot of special effects and other fancy stuff that you don't need. As a related aside, a few weeks ago I recorded signals bounced off the moon from Arecibo from outdoors using a home made yagi and my FT-817. My recording device was a netbook. The signals were extremely weak but barely copyable. When I played back the WAV files on the shack PC using a USB sound card as the audio all I heard was noise. I then "borrowed" the internal sound card from the K3 to use for audio playback and heard the signals exactly as I did originally. Proof positive for me that USB sound cards do deliver a poor quality signal. ----- Julian, G4ILO. K2 #392 K3 #222. * G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-and-USB-Audio-Codec-tp5277614p5279876.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
