Tvheadend

Hello all,
Perhaps someone can shed some light on this.... I have cable tv
and I got a new tuner card which is an 1800 hauppage. Now here is the question
In tv time It logs right in picks up the channels and plays no problem... Now in digital
qam it does pick up SOME channels that are broadcast in the clear... However it will not pick
up on atsc.... and I do not understand why I used scan tv and at 66.5 mhz there is a channel
well Of course tvheadend will only access khz so what i did was use a frequency converter
and converted it to KHZ well i figuered that would get it.. Well to my suprise...... No...
it didn't can anyone Anyone at all shed some light on this?!?!?!??!

Thank you
                     Mondo