I chose this forum because of an excellent thread titled "Antenna Length & Resonance" that seems to be highly related, though I cannot apply what I read there. I know the forum name does not quite match, please redirect me if appropriate.
I need to run audio cables through a set of 1-1/4" electrical conduits (EMT) under a stage for physical protection. The conduits will be under a stage about 200 ft from the base of a 3KW 150ft FM broadcast tower (I assume that the frequency is just another parameter and so not important to the discussion). I am concerned that certain lengths will resonate and that this might be a problem either for the radio station or for the audio cables or for someone touching the conduit! I also expect that this will be an improved situation with respect to shielding, though right now they pick up three stations other than the one being broadcast from this tower.
Question 1: Will this happen (I think yes)? What specifically will happen... will there be a stationary voltage profile along it, or what? How can I calculate the voltage?
I am thinking that it might be good to ground it at the transmitter for safety reasons, through a ferrite toroid that is lossy at the transmitter frequency to discourage interaction with the transmitter or the transmission pattern or it does not result in transmission frequency current to ground while not building up for example a static charge as a floating metal object. I realize that the wire from the conduit to the transmitter will not be an RF ground because of its inductance and huge length, but the primary purpose is to suppress static charge while not becoming a counterpoise of sorts with unknown consequences.
Question 2: Please comment on the conduit floating vs. grounded subject.
Question 3: How can I calculate the frequencies at which it will resonate, and the frequencies that are maximally not resonate? How precise do I need to be? How do I convert this to lengths? How can I measure what is going on so that I can confirm that the lengths that I choose are doing what I want (Namely nothing!)?
Thank you for helping me to understand!
--Ray
I need to run audio cables through a set of 1-1/4" electrical conduits (EMT) under a stage for physical protection. The conduits will be under a stage about 200 ft from the base of a 3KW 150ft FM broadcast tower (I assume that the frequency is just another parameter and so not important to the discussion). I am concerned that certain lengths will resonate and that this might be a problem either for the radio station or for the audio cables or for someone touching the conduit! I also expect that this will be an improved situation with respect to shielding, though right now they pick up three stations other than the one being broadcast from this tower.
Question 1: Will this happen (I think yes)? What specifically will happen... will there be a stationary voltage profile along it, or what? How can I calculate the voltage?
I am thinking that it might be good to ground it at the transmitter for safety reasons, through a ferrite toroid that is lossy at the transmitter frequency to discourage interaction with the transmitter or the transmission pattern or it does not result in transmission frequency current to ground while not building up for example a static charge as a floating metal object. I realize that the wire from the conduit to the transmitter will not be an RF ground because of its inductance and huge length, but the primary purpose is to suppress static charge while not becoming a counterpoise of sorts with unknown consequences.
Question 2: Please comment on the conduit floating vs. grounded subject.
Question 3: How can I calculate the frequencies at which it will resonate, and the frequencies that are maximally not resonate? How precise do I need to be? How do I convert this to lengths? How can I measure what is going on so that I can confirm that the lengths that I choose are doing what I want (Namely nothing!)?
Thank you for helping me to understand!
--Ray