You can keep adding them as long as the DVR software you're using will let you. Some have limits on the number of tuners that can be used. But yes it does work like that - two dual cards = four tuners = four recording streams at once.
Only one line is needed from your antenna, but it will need to be split for each card. So two dual cards means the line needs to be split into each card. The cards themselves split the signal for each tuner.
Be careful that you actually buy a "dual" tuner. There are a lot of marketing terms like "dual," "hybrid," and "combo." You need two independent tuners on the card. Mine has one digital and one analog, and I think it was called a "combo" tuner. I could only ever record one thing at a time.
Only one line is needed from your antenna, but it will need to be split for each card. So two dual cards means the line needs to be split into each card. The cards themselves split the signal for each tuner.
Be careful that you actually buy a "dual" tuner. There are a lot of marketing terms like "dual," "hybrid," and "combo." You need two independent tuners on the card. Mine has one digital and one analog, and I think it was called a "combo" tuner. I could only ever record one thing at a time.
