You might try this...

http://www.youtube.com/watch?v=ke5wq0DZr7Y

I tried it but it can not send files. The morse code function on it is also bad quality and works intermittently.

Why can't you just use a Modem on each PC?

I was wanting to find a software modem that uses the built in audio on the computer so that I can send and recieve any type of file. I would then have the modems connected via radio or wire.

Why not ethernet?

You mean a softmodem...and using HyperTerminal?

http://en.wikipedia.org/wiki/Softmodem

http://technet.microsoft.com/en-us/library/cc751104.aspx#XSLTsection129121120120

Have you tried the software at this link called AGWPE

http://www.soundcardpacket.org/

This software is intended to act as a Packet modem on a sound card for transmission over a radio. I don't see why it wouldn't work between two computers and no radio however.

This software does say it works on windows 7 but that depending on the soundcard you have some people have reported issues.

I have never used the software, but I hope it works for you.

It appears the OP is explicitly looking for a file transfer mechanism that uses the sound card line in/line out as the physical layer.

I don't think suggestions of the myriad USB, Ethernet, Serial, Wi-Fi, Bluetooth options are what he was looking for.

(This sounds like a throwback to the old "cassette tape" storage and retrieval system I used on my TRS-80)

I found software called J-QAM that is supposed to do it but it only has some settings and no data transfer option.

LOL! I remember those... Opps

Something like this?

http://www.linux-ax25.org/wiki/Soundmodem

What type of file?

You want the transmission path to be audio?

Objective is file transfer or what?

Please describe your requirements again.

I am wanting to convert a file to sound and send it along a wire or through a radio to a recieving computer where the sound will be decoded back to a file.

Why?

So I can send data through a radio.

Try these guys.

That website does not seem to show any data over radio stuff.

Go to the bottom of the home page and enter "file transfer" as the keyword and press the "go" button.

You'll find stuff.

Damn, missed my 15 minute edit window here by about 30 seconds, and the "off-topic" box ended up being checked, to boot!

Here is the edited, on-topic, posting:

Googling "sound card" "file transfer" found some interesting links: Click Me

Useful Wikipedia Entry on line coding

How Atari recorded to cassettes

You want a modem to do this. That's why they were invented. If you want to send by radio specifically then Tait TM8100 does it when correctly optioned. Software can't do everything.

I don't think the OP is looking for alternatives for the best, cheapest, fastest, easiest way to send files.

It sounds to me like he is simply saying:

"I have two computers with sound cards. How can I connect them through the sound card ports and send files back and forth?"

But he has also mentioned he wants to send files via radio, and there are other solutions for that, as you mention.

You'll be able to send files using an audio modem somewhere on the order of 300 baud and down...that's baud, not even 1K...as in the old modems of latter day that ran 1200 baud...from about 1984...and those were top end models. A file anywhere near 500K would take about an hour to transmit and receive. Remember those days? We used to put a cassette in a deck, plug in the telephone handset and pray that no extraneous signals would interrupt the loading of our program data or else we would have to start over again.

The bandwidth on this type of device would be exceedingly low, hence the data transmission rate...and no error checking would be available...we don't even use that level of error checking anymore since it is not needed.

Sending the files over radio is totally different...that would be modulated sound using a radio carrier...let's say 540kHz...that's at the lower end of the AM band in the US. Now the bandwidth is significantly higher since the carrier alone is in the kHz range...but now you're getting right back to the argument of why not just use a modem?