Andy,

Grants explanation of I/Q modulation is excellent.

Perhaps your conversation involved using complex sampling (I/Q) to double the bandwidth compared to simple sampling. The usable bandwidth is limited to about one half the sampling frequency (google NYQUIST). When looking at faster convertors you reach a point where doubling the conversion rate more than doubles the cost, or a convertor that fast may not exist. By using two simultaneous convertors, sampling the I and Q signals, the usable bandwidth is doubled.

If two channels are available, there is a way to double the data rate without involving the I/Q signals. Of course I am speculating about the nature of your conversation, so I may be way off.

Hope this helps. '73 de Ed N8BBQ