Sound Card Digital Interface question

Discussion in 'Working Different Modes' started by W0BTU, Jul 14, 2011.

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  1. W0BTU

    W0BTU Ham Member QRZ Page

    Digital Modes Interface question

    I'm wondering what the practical advantages are (if any) of commercial digital mode interfaces with their own sound card, such as the SignaLink, RIGblaster, RASCAL, etc.

    For PSK31, etc., all I have here between my computer (using Fldigi) and my Icom transceivers is a very simple homebrew interface: It uses two audio transformers and about 4 resistors. No USB or serial port connection, no adjustments, no software drivers, and no PTT connection, either (it uses the transceiver's VOX).

    What am I missing by using such a simple interface vs. one that costs ~$100? Is something going over my head here?

    I see people with these commercial units complain about (among other things):

    • My computer doesn't have a serial port, and so I can't use it.
    • I'm having trouble installing the drivers supplied by the manufacturer of the interface.
    • Why is this so complicated?
    • ... and the list goes on.

    1. Why do we need to use a USB or serial port to get on PSK31 or other digital modes?
    2. Why do I need a separate sound card?
    3. What's wrong with using my computer's sound card?
    4. What is the driver software needed for?

    I have all three of my hearing aids at maximum. Please educate me. :)
    Last edited: Jul 14, 2011
  2. K0SPN

    K0SPN Ham Member QRZ Page

    I have a SignaLinkUSB.
    The biggest advantage for me is that it's a separate sound card.
    My computer is used for everything, not just radio stuff, so it's convenient for me to have it separate to:
    a) Not have to fiddle with levels when changing usage from radio to games, YouTube, etc. (I know there are programs that can do this automatically, but again, that's fiddling with it, to me)
    b) Not have to worry about compliance because of accidentally transmitting regular computer audio
    c) Gives me easy access to I/O levels when I do need to change them slightly

    So, you don't need USB or serial connections to do ASFK modes.

    Some people use the same, or similar, interface you have but use a second, internal, sound card, which essentially is the same as using an outboard unit, and this gives certain advantages, like described above; also, sometimes the internal sound chipsets are not very high quality (or are otherwise noisy), so you have reduced performance versus a discrete internal or external setup.

    There is nothing wrong with using the sound chip already in your computer, as long as you know and understand the abilities and limitations of said chip. They're usually perfectly acceptable for what we use them for.

    Drivers tell the OS how to interact/communicate with a piece of hardware. Whether it's a sound card, printer, mouse, serial port, scanner, camera, HDD/SDD, etc., everything needs a driver (some drivers are integrated into the OS, so they're still there, you just don't install them individually). See:
  3. W4PG

    W4PG Super Moderator Lifetime Member 279 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    I think the main reason is to not tie up your sound card. My US Interface Navigator has its own sound card built in, so I can still use my computer for sound when needed. Additionally, the CI-V info from my Icom plugs directly into the TNC, which then plugs into the computer via a USB port. Why is that needed? That port contains all the rig information and computer access for computer control of the rig. All the QSO information is automatically entered into the log as well.

    Of course, my new IC-7100 has all the CI-V information and sound running through a single USB port, so I don't NEED a TNC to work digital modes with it. That's really nice!

  4. K7MH

    K7MH XML Subscriber QRZ Page

    If it is working for you then that is all you need!
    Hopefully it has isolation for the signal paths.

    I think a lot of that is just people that are not very computer savvy rather than real issues with a commercially made interface.
    The people that don't have any problems you won't hear anything from.
    Last edited: Jul 15, 2011
  5. KR2D

    KR2D Ham Member QRZ Page

    I'll go along with what others have said - it adds a second sound card. The other stuff in high end commiercial interfaces is nice, but not necessary. In my opinion, a second sound card is necessary for digimodes.

    Until 2 weeks ago, my shack computer was set up exactly that way - I had an ancient Sound Blaster Live! installed for digimodes. I have built a new system that is 64 bit and runs Windows 7 64 bit, and alas, that ancient Sound Blaster has no drivers for Win 7 64.

    So facing the prospect of replacing the sound card anyway, I started researching my options. I decided an additional requirement was something with knobs for easy adjustment. There are external USB sound cards available, one of those would work just fine. The Signalink USB is nice, but in my opinion, not worth $85 to $100. The other external devices from MicroHam, US Navigator, Rig Expert are very nice and add true FSK, CW, PTT, CAT interface, etc but cost hundreds of $$$. Nice, but I already have PTT (serial port), CW (Winkeyer USB), and a CAT interface. If I want true FSK, I can build a serial port interface for a few dollars.

    If I didn't already have the Winkeyer, CAT cable, and PTT interface and I didn't know how to build them (or didn't have time) then a Navigator, MicroHam, etc would be tempting.

    I went shopping for an external sound card with knobs, but found a used Signalink USB for $50 with the cable to match my rig. So for $50, I went with the Signalink. It's easy to use and just works - plug and play.

    If you just want a second sound card, internal (PCI) or external (USB) cards can be had for $15 or so (or you can spend big bucks, too).

    Those commercial interfaces are much neater, too: only 2 cables to connect. USB to the computer, and a cable to the rig.
  6. W0BTU

    W0BTU Ham Member QRZ Page

    Ok, I can appreciate that. I've never used my shack computers for anything but ham stuff.

    I like that idea. That solves a) and b) etc. above.

    This I understand, I just worded the question wrong. Never mind. :)
  7. W0BTU

    W0BTU Ham Member QRZ Page

    That's what the two transformers are for. My last interface didn't even need those, because there was no ground loop.

    I suppose.

    I just cannot fathom why more people can't build something so utterly simple! Don't ask me to explain, but buying something that somebody else made --that I can make myself without a lot of time and trouble-- would take much of the fun out of it for me. I don't buy commercial antennas for the same reason.
    Last edited: Jul 16, 2011
  8. M3KXZ

    M3KXZ Ham Member QRZ Page

    Personally, I just can't be arsed when I can pick up a ready made one with audio transformers, opto-isolated keying circuit, enclosure, leads, moulded audio plugs, USB plug etc for £25. But they're proper fun and interesting.
  9. N4EYZ

    N4EYZ Premium Subscriber QRZ Page

    I remember building anytime it was within my abilities. Built my first rig from a kit--33 yrs ago, Heathkit of course. After that I did what I could, or had time to. Then came children and spare time went away! Wouldn't have done any different though. Now I have time but limited abilities due to some hand paralysis from an illness---but it's improving. Just getting back into this hobby and I've learned alot from reading what all you guys and gals have to say. Thanks!

  10. W0BTU

    W0BTU Ham Member QRZ Page

    I posted this on July 14. Today, it's September 14.

    And so far, no one has given me any reason why we need a PTT line between our computer and radio to operate PSK31.

    I'm all ears. :)

    One thing that still I wonder about is, do any of the digital-mode commercial products (Signalink, Rigblaster, etc.) let us operate PSK31 so that we can use our transceivers' narrow CW filters?
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