Tvheadend

My TV tuner USB stick seems to be a lot less sensitive than my TV. Often when I try to watch TV through Tvheadend, I'm told "no signal" while the signal's strength is well above the minimum for my TV. I suspect that's because my tuner is sometimes off-frequency. Exactly what frequency are you supposed to give to the "muxes"?
I have a lot of confusion, but there's this one station that transmits on channel 25 and according to Wikipedia that's on 537250000Hz. Well, that didn't work, so someone told me I should use 53631000Hz. That didn't work, but then somehow a "mux" just showed up using 539028615Hz, and finally I was able to map a service. But I still think the frequency is a bit off, so how do I know what the exact frequency is that Tvheadend expects?