Ok so it seems that there is some argument as to why its only intermittent.
first off the station that is interfering is not likely to be fluctuating in
power unless it is making
pattern changes throughout the day but that is not normal for small stations nor for FM. usually only for AM where the
power is lessened at night in some cases, or the
pattern is modified to prevent interference with other stations on the same frequency at night.
Equipment that has poor shielding and week RF suppression is more susceptible to AM than FM is true but FM is quite possible I Have an FM crystal radio that exploits poor shielding the ability of a fast
diode to detect an FM signal when tuned off frequency. it will receive all four FM stations in my area. look Ma no batteries or
chord!
intermittent
RFI can be caused by many things.
Inter-modulation if there are other additional transmitters that are near by such as communications repeaters or the dreaded
cell phone tower that sells space to pager companies (yep pagers still exist), that only transmit some of the time the frequencies of all of the stations can mix in the receiving device in this case the
Amplifier. when this happens you may hear one or the other station or even both at the same time. It would take too long to give the full technical reasons behind this on this forum but I assure you inter-mod is not an uncommon problem. many cheep electronic devices suffer from inter-mod problems. just ask people that live near a communications tower that buys electgronics at the dollar store.
another cause of the intermittent nature is location of equipment. Even if the receiver or in this case the guitar amp is stationary,other objects moving around it can
effect how much RF is being received. and not necessarily items in the same room or building. even an aircraft overhead can cause minor changes to the
pattern of an FM signal and how well a recieving device picks it up. this too will
effect the intermittent nature of the interference.
last is atmospheric conditions. this will have less
effect on nearby transmitters but will have some.
I am sure there are other people on this group that have radio experience that can help here I have been a ham for only a few years but have worked with RF for a long time
in one way or another.
if you find some of the clamp on fer-rites go ahead and try them they don't cost much and can even be found in used scrapped TV's
etc. you don't need supper quality or fer-rites rated for GHZ just the garden variety Radio shack ones will do. if you can wrap a few turns passing through it the better.
Good luck!
