He's more correct than you think. Since the 90s there's been an explosion of sound card based digital modulation schemes. Usually you see a waterfall spectrum from 0 to "whatever" and you click where you want to operate. Essentially the attached SSB transceiver is a linear transverter from audio to some RF.
So instead of tuning your radio to 7.070 MHz and clicking on the computer waterfall at 1200 Hz (aka operating at 7.0712 MHz) you just unplug the radio from the computer, use speaker and mic instead of something plugged into speaker and mic jacks and click on 18 KHz or whatever.
In the early days of PSK-31 and other modes you did demos at radio club meetings and whatever by just letting it rip over the speakers. Loud and annoying but works pretty well across a room or further.
The main limitation is most SSB communications radios cut out around 3400 Hz at the high end so the software that is written for sound card digital modes cuts out somewhere above that, but sometimes not as high as 25 KHz or whatever, because 99% of the users and devs will never fool around with ultrasound.
Because I like to use a HF modulation mode called Olivia I mostly use an old version of DM780 software (from when it was free) and multipsk (free) although I could use FLDIGI (which is also free). In my infinite spare time I'll see what unnatural limits have been built into the software. This topic of ultrasound networking comes up on HN like clockwork every week or so, so I'll report back next time.
(Edited to add, one thing I like about multipsk is the, um, innovative UI. Go to images.google.com and take a look.)
So instead of tuning your radio to 7.070 MHz and clicking on the computer waterfall at 1200 Hz (aka operating at 7.0712 MHz) you just unplug the radio from the computer, use speaker and mic instead of something plugged into speaker and mic jacks and click on 18 KHz or whatever.
In the early days of PSK-31 and other modes you did demos at radio club meetings and whatever by just letting it rip over the speakers. Loud and annoying but works pretty well across a room or further.
The main limitation is most SSB communications radios cut out around 3400 Hz at the high end so the software that is written for sound card digital modes cuts out somewhere above that, but sometimes not as high as 25 KHz or whatever, because 99% of the users and devs will never fool around with ultrasound.
Because I like to use a HF modulation mode called Olivia I mostly use an old version of DM780 software (from when it was free) and multipsk (free) although I could use FLDIGI (which is also free). In my infinite spare time I'll see what unnatural limits have been built into the software. This topic of ultrasound networking comes up on HN like clockwork every week or so, so I'll report back next time.
(Edited to add, one thing I like about multipsk is the, um, innovative UI. Go to images.google.com and take a look.)