Originally Posted by Rob
Whatever a transponder is.
It's actually a satellite term, but I know what they are getting at. Several channels are bundled together on the same frequency. I don't know the Smallworld channel line up, but as an example on Virgin Media, BBC News, BBC Parliament and the BBC radio channels are all on the same frequency. If you happen to want to record two channels from the same frequency, Topfield boxes can do it using a single tuner tuned to that frequency. However, they only have two tuners, so can't record say 3 channels from 3 different frequencies.
The problem is knowing which channels share a frequency. I'd be surprised if Smallworld publish that info, so it would be trial and error. Also channels can get moved between frequencies from time to time, so the info becomes out of date.
So in summary, only rely on being able to record two channels, and you can't watch a third at the same time.