RF, which stands for Radio Frequency, is the very high frequency (well above human hearing) electromagnetic signal (not sound) which carries the sound signal we hear on AM or FM radios as well as the sound and pictures that we see on TV. Electromagnetic signals do many other things. From lower to higher frequency, the electromagnetic spectrum goes like this:
We are, literally, continuously bathed in low level electromagnetic radiation. Some of it carries sound information, much of it does not.
It is possible for audio (sound) electronics to pick up and, in some cases, decode the sound information carried by electromagnetic waves. When that happens your guitar or bass may channel sound intended for radio receivers into your amplifier head where it may be heard quite clearly.
This is most likely to happen if you are playing near radio station transmitting towers. It may also happen if you play near an amateur (ham) radio station. Or you may hear R2D2-like goings on if you are playing near a computer and so on. When it interferes with what we are doing it is called RFI - Radio Frequency Interference - and is seldom welcome.
HOW TO GET RID OF IT?
With one or more of the many techniques that have been developed since the invention of the radio.
Simple trapping with 1 or 2 capacitors
- at your pickup selector switch (in 2 vol. instruments with switches) or
- at the outer ungrounded lug of the vol. pot of a Strat* type harness or
- at either outer ungrounded lug of a J-Bass* type harness
- at the hot lug of the output jack:
Solder a small value capacitor from "hot" to ground keeping the lead of the capacitor nearest the "hot" lug as short as possible (1/4" or less but taking care not to overheat the capacitor).
Capacitor values: 47pf, 68pf, maybe as much as 100pf. Two of these along the signal path of the guitar may barely affect the highest treble note of a guitar. They will however look like very low value resistors to an incoming Radio Frequency signal. They will "shunt" the RF signal to ground.