My experience is that 4 ft tube RFI comes from the ballast, either the commercial type (often sold in box stores) and the "residential" type both cause unacceptable RFI, especially on the BCB band and 160 meters. I bought 4 ft. WERKER ballast bypass tubes from batteries plus bulbs. simple to rewire the fixture. NO RFI and you save lots of power getting rid of the ballast completely. Also ballast failure rate is about 5 % a year. Do not use a plug and play LED tube, which still uses a ballast. Folks have posted that Hypericon (spelling ?) also makes no RFI tubes which require the rewire of the fixture and get rid of the ballast. I have rewired about 150 fixtures (350 ? tubes ?) most between 2 and 4 years ago. No failures yet and some run many hours a day. About 1% failed out of the box, but I got free replacements.
Some fixtures require replacement of a tombstone on one end of fixture, but it is easy and I think they cost 40 cents each. Rick kL7CW