. At the age of 15 you said you made your own speaker and the coil windings oxidized. Are you implying that this was not (insulated) magnet wire? FYI, a semiconductor junction means just that ... "JUNCTION". The semiconductor isn't formed by oxidation alone. It's formed between an oxidized junction of two conductors.
Well I guess it is likely that from my lack of skills I overlapped the windings somewhere creating the junction. The wire was uninsulated and the speaker stopped working completely no matter how new the battery was after two weeks after winding the coil, at the same time that I noticed that the wire on the wire spool in the project kit was a bright shiny copper, compared to my wire on my winding was a dull color like an old penny, so I deduced that that's why it stopped working because the copper oxidized.
That said I'm having a hard time swallowing your speaker story. Was your home a tower house sitting in the 50KW RF field?
Well there is the chance that I'm just insane and the voices heard under my bed with the speaker not connected to a battery were halucinations.
Please stop repeating "Inductive" Antenna. They're not inductive. We've told you that they're not inductive. No matter how many times you insist on repeating that erroneous statement it won't make it so.
I must be confusing antenna with a transformer with an air core the size of a room to induce audio frequencies from primary winding to secondary winding. So there is no such thing as "inductive antenna", what i was referring to was actually a transformer with an air core.
I told you before that antenna and transmission line theory can and will fill an entire text book. A transmitting antenna is a resonant circuit. By definition a circuit becomes resonant when inductive reactance and capacitive reactance are equal. At this point reactance is zero. All that's left is the DC resistive component of the transmission line and antenna conductors. Typically this value is well under an Ohm except for very long transmission lines. So where's the 50Ω you ask?. It's an 'apparent' resistance. It's what the transmitter sees looking into the input end of the coax. It's also what the output end of the coax sees looking into the input of the antenna. The purpose of a transmitting antenna is to radiate RF energy. Stated simplistically the RF escaping the antenna gives the appearance of the RF being fed into a 50Ω resistive load.
Oh okay, so the actual DC resistance of the feed line and antenna combined is usually under an ohm except for very long feed lines. but as I had disasterous results connecting a tube amp speaker output to a speaker cable connected to a metal pole, apparently the resistance of the feedline and antenna is not what provides the load of the transmitter to prevent the transmitter from being destroyed. What actually provides the load is the RF escaping giving the appearance of a 50 ohm resistive load.
So since audio escaping is not RF, no 50 ohm resistive load and amp goes into over saturation. So presumably if the oscillator was placed before the tubes (which assume that these tubes can handle RF without accidently demodulating it), would that allow the transmitter to perceive the necessary 50 ohm resistive load?
A 1/4 wave ground plane antenna has a 50Ω characteristic impedance but not all antennas have a 50Ω characteristic impedance. In those cases the input of the antenna employs a matching network. Also, 50Ω coax is an unbalanced transmission line while some antennas are balanced. In these cases the antenna input employs a ballun to convert the unbalanced transmission line to the balanced antenna. The ballun can also correct for an impedance mismatch between the coax and antenna. A Ballun is basically an RF Transformer.
I thought you said the DC resistance was well under an ohm? Is that the whole point, impedence only exists when there is current and frequency, but D.C. resistance is always there?
So since impedence is frequency dependent (we skipped the chapter on alternating current in my physics class but I read it anyway and was confused), an antenna will not exhibit a large enough impedence load at audio frequencies (as i found out when I destroyed my amp), but the impedence load will be enough at radio frequencies?
Last note: Please don't post "Inductive Antenna" again.... EVER!!
Okay. I think I meant transformer.
conduction speed ???? come on now dieter where did you find that reference ?
maybe you really mean propagation velocity ? but it decreases with an insulated wire compared to a bare wire. .....
actually copper oxide is still a respectable conductor and a fine film (layer) of copper oxide doesnt affect VF to any significant extent. Covering the copper wire with a plastic insulation has a much more drastic and measureable effect
Dave
Hhm, then my physics teacher and biology teacher both lied to me. They both told me that nerves coated in mylein sheath have a faster conduction speed and they told me that the same is true for wires.
davenn said:
As I said in my previous post the tiny thin film of copper oxide doesnt really affect things to any measurable significance
at least not untill you get up into the microwave frequencies, well above 1GHz. Bare copper (other than in waveguides) is rarely used rather it will be tinned or silver plated
Oh, so copper that is uninsulated is usually tinned or silver plated to prevent it from oxidizing, while my science project kit had truley bare copper wire, maybe intentionally to demonstrate oxidation and to demonstrate crystal sets when the coil windings of the speaker oxidize enough assuming that the kid who assembled it probably over lapped a coil.