Before revision: Without using an IF, all the complicated filters and detectors in a radio or television would have to be tuned in unison each time the frequency was changed as was necessary in the early tuned radio frequency receivers .
After revision: (TRF)Without using an IF, all the complicated filters and detectors in a radio or television would have to be tuned in unison each time the frequency was changed as was necessary in the early tuned radio frequency receivers .