Channel 6 was just below 88 MHz, u use to be able to tune the audio of channel 6 by tuning just below 88 MHz. Not sure where 7 began but there is quiet a bit of communication services in there (ie land mobile, fm brawcast, weather, amateur, etc)
My radio has its own antenna on the side of the trailer. I would suggest pluging another antenna in to the radio and see if can get anything. Try and determine if it is the radio or antenna. A piece of bare wire abt a foot long should work enough to see if the radio works (the center conductor stripped bare of the onsulation and brad will be the right size and should work).
I'm not familiar with ur setup. The older ones had their own antenna and didn't use the tv antenna.