What is difference between interface & just using cable & sound card (PSK31)?

[W8ATT]

I have a Icom 756 Pro III that I want to run PSK31 & RTTY with but want to know what is the difference between using a interface, such as RigExpert or Rigblaster, or just using a cable from my ACC port on my radio & use software to run PSK31 or if its not possible to run w/o an interface. What are the advantages of using an interface opposed to just using cable & software? I have a older Rigblaster Plus with a serial hookup but don't have a serial port on my computer running Windows 8. Any help would be greatly appreciated as I was running PSK31 quite a bit with my Kenwood 2000 but sold it & got the Icom instead & haven't run it yet. Thanks, Scott W8ATT

[AA4PB]

For one thing you need an interface for the PTT signal. That can be as simple as a single transistor that grounds the PTT line when voltage is applied from a serial port control signal. The other advantage of an "interface" is that it includes transformers to eliminate potential ground loops caused by connecting the shields to the ground connections on the sound card and the radio. An "interface" also provides resistance attenuators to set the signal levels appropriatly.

An interface can be pretty simple to build. You can find lots of techinical information on the Internet. In some cases the "interface" can be as simple as a few resistors and an NPN transistor.

Some interfaces like the SignaLink-USB contain their own internal sound card which simplifies the wiring down to a single USB cable going to the computer. It really doesn't provide any operational benefit, other than convienience, over using the computer sound card and a simple audio/PTT interface.

[W8ATT]

The cable I saw must have had the interface as you describe built within the cable. I thought I saw a cable that had isolation & that it was software driven thus my confusion over the issue.  I knew before about having isolation to prevent the ground loops was essential. I'll have to check out the plans online & find one that will work with my Icom radio. Thanks for your input & time.

[VA7CPC]

See if the IC-756 supports "digital VOX" -- that is, VOX triggered by a digital (probably called "packet") audio signal.

If it does, you don't need the PTT line or serial port.

If it doesn't, you might want to try a USB-to-serial adapter, and use your old PSK interface (if you still have it).  There are two different chips available for those adapters.  I found that FTDI-based adapters worked OK under Windows 7, and Prolific-based adapters didn't.   I don't know about Windows 8.

The transformer coupling is useful for lots of people -- it avoids RFI.   "Direct coupling" (wires) from the computer's soundcard to the rig often need ferrite beads (or more!) to avoid RFI.

.            Charles

[K5TED]

You can build or buy a CAT cable, and build your own audio interface from scratch or using a common stereo "ground loop isolator" or "hum eliminator", and some cables/adaptors. Loads of fun and a tangle of cables and possibly RF noise to deal with afterwards. Of course you can also build your own very elegant interface combining all the good engineering practices in the way of signal level matching, RF suppression, ausio isolation, case design and all the good fun of rolling your own.

Or...

Plunk down a few bucks for a Signalink and be done with it. One cable to radio, one cable to PC. Fun.

Been there, done that. I now own two Signalinks. They work flawlessly.  I still use the simple CAT cable and audio transformer setup on one radio as well.

[N4CR]

K5TED has it right. The only real difference between the two is convenience and the path of least hassle. You can build one just as good given time/materials/design skills/perseverance, but the short path is to plunk down some change and start having fun.

Not to mention that there's some low cost mods to the SignaLink USB that makes it even better than it comes from the factory.

[NK7Z]

I have a Icom 756 Pro III that I want to run PSK31 & RTTY with but want to know what is the difference between using a interface, such as RigExpert or Rigblaster, or just using a cable from my ACC port on my radio & use software to run PSK31 or if its not possible to run w/o an interface. What are the advantages of using an interface opposed to just using cable & software? I have a older Rigblaster Plus with a serial hookup but don't have a serial port on my computer running Windows 8. Any help would be greatly appreciated as I was running PSK31 quite a bit with my Kenwood 2000 but sold it & got the Icom instead & haven't run it yet. Thanks, Scott W8ATT

Hi,
An Interface, usually has a set of isolation elements within it.  This serves to isolate the radio from issues such as hum, RFI, etc...  A Cable will not... 
Interface is a word used as a defacto statement that something beyond a cable is in use...  Technically a cable with ends on it is an interface, however, of late, (last decade or so), Interface means a box of some sort... 

I have a review of the Rigblaster, which touches on some of the functions of that Interface at:
http://nk7z.net/rigblaster/

[KB1NXE]

Not to mention if Windows Sounds are turned on, every time you make a mistake a "Tink" sound will be transmitted.  Or worse!