Nintendo 64 problem with rf adapter

[BenKnox]

I've got an N64, but i have to use an rf adapter because my highdef tv doesn't have the red white and yellow av ports.  The only problem is that whenever I turn the N64 on and go to the correct channel, it says "weak or no signal." My av adapter is one of those universal ones and it works just fine with my xbox 360, so that makes me thing that the N64 just isn't powerful enough to send an audio video signal to my tv.  So i was wondering if there was an semi-easy way to mod the n64 to make it send a more powerful signal.  Im pretty much a noob at system modding so any help you could give me would be much appriciated