My AM transmitter is set up in my basement and for some time now I have been hearing strange intermittent interference on my transmitted signal as monitored by my BC-1004-C vacuum tube receiver. This interference was present as a scratching sound which could be caused by a loose or corroded connection but none were found in either the transmitter or receiver wiring. I had noticed that the noise was worse when the furnace was running or when someone was walking on the floor above suggesting vibration might be a factor.
Unrelated to this I embarked upon a project where I needed a small piece of aluminum and I retrieved a roll of aluminum flashing which I had stored on the top of a partition here in the basement. I noticed that after I had removed the flashing that the noise was gone. Pursuing this I noted that when the flashing was stored it was touching a water pipe on the ceiling of my basement. Apparently the poor contact between the oxidized aluminum and tarnished copper pipe was the source of the interference.
In previous experience with repeaters I learned that corroded or poor metallic connections nearby can be death to receiver performance. The non-linear electrical characteristics of these connections produce interference effects from strong RF and apparently that was in play here.
I mention this so maybe someone plagued with a similar noise problem will find a similar cause and cure.
Neil
Your lucky discovery of the very secret and unlikely source of the interference brings two thoughts to my mind, one ridiculous and the other from experience:
The "ridiculous" thought is that your "telegraph key," the aluminum touching the pipe, could have been used by spirits to send messages from "the other side."
Now experience: for awhile I had a static much like lightning static that happened when I walked in a particular location, and that happened to be near a central interconnection point of audio, video and computer equipment. I never did find the exact source, but the problem stopped, so I must have inadvertently moved whatever was causing the static.
I recall hunting down a similar problem in a full power 100Kw ERP FM site where something was causing a clicking/scratching noise on the station's signal.
I started the investigation at the studio, going through every wire, every connector, every rack, every coax, every power outlet, every power cable, every piece of equipment in the place..to no avail. The next step...the transmitter site.
The process repeated at the TX site, inspecting every piece of equipment, every cable, every connector, every rack, on and on, till finally the problem was located.
It ended up being an issue with the resonant cavity which houses the power tube. A few of the lock down screws holding one side panel of the cavity had come loose, due to vibrations from the forced air cooling fan motor. It had worn its rubber mounting bushings out and the motor was dancing, beating against the side a structure railing which was attached to the base assembly plate of the cavity.
Re-securing the screws with lock-tite and lock washers solved the problem.
An example of how deep those hidden gremlins can be. But sometimes those gremlins can cause just as severe a problem with a simple thing as a roll of aluminum sheeting tapping against a water pipe.
But that is what makes this all so much fun...discovering that a problem does not always mean it is caused by something serious...it can be something so simple and so out of the norm that who would have guessed first it would be a roll of aluminum foil tapping against a water pipe due to vibration of someone walking across the floor, or a few loose screws inside a cabinet housing a 25Kw power tube.
RFB