I don't recall why I do this! so I may just have it wrong - my tuners still work but perhaps they (the drivers) or some other part of the dvbt network do a search.
I'm sure i read on the Linux-DVB development mailing list that some cards will auto adjust for the offset. You can give them either frequency and they get the right one. Doesn't happen with all cards though. I also think it is in the card rather than the drivers.
Germany
