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Looking for resistor value and capacitor value for passive low pass filter remove RF

davenn

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So If I'm only supposed to have one turn on the inductive antenna, then I imagine that I should use a thicker gauge of wire rather than stereo speaker wire. The schematic says to use #18 bare copper wire. I can buy some on Amazon with my next shipment for only $2.10 (the one that is called "artistic wire").

it doesnt need to be thicker. Increasing the diameter of an antenna wire or aluminium tube just increases the bandwidth.
 

dietermoreno

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Well so then that is the reason why the schematic uses such wire gauge, because FM broadcast band (VHF) uses wider band width for each station than AM broadcast band (MW).
 

(*steve*)

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Well so then that is the reason why the schematic uses such wire gauge, because FM broadcast band (VHF) uses wider band width for each station than AM broadcast band (MW).

No, it's probably because they wanted to use wire with structural properties, i.e that it would stand up by itself rather than need additional support.
 

CDRIVE

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There is of course skin effect as frequency increases but I think Steve nailed it. It's what I would have done too. Speaking of that gentleman's construction practices ... I like them very much. Crystal radios should be show pieces, which he certainly accomplished.

Chris
 

dietermoreno

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Oh okay, so the thicker wire gauge for antennas rather than connecting wires is entirely for mechanical purposes, since a long thin wire moved around a lot (as can be the case for antennas) is subject to tearing, such as the stereo speaker wire gauge that in my car connects a dummy cassete tape to a stereo phono jack (for connection to a digital music player) and one wire is already fraying at the jack after only purchasing the adapter 4 months ago as I move around the wire every day everytime I insert and remove the cassete tape.


The schematic that I showed for FM crystal set used uninsulated #18 copper wire for the indoor inductive antenna, but doesn't copper oxidize and isn't that the whole motivation for insulating copper wires (in addition to increase of conduction speed)?

When I built a speaker from a science project kit when I was 15 years old where I wound my own speaker coil, I found that after about 2 weeks my coil had oxidized and no new batteries would allow the speaker to make sound (and before it oxidized some really interesting things happened, the speaker started to pick up the local 50kw MW transmitter 780 KHZ WBBM if I put my ear up to the speaker, and the sound was louder when I connected the speaker leads to a 10 foot long aluminum foil duck taped together antenna, presumably copper oxide acting as a diode, it actually got louder as the wires oxidized more and i could hear voices coming from under my bed (where the speaker was stored) while I was in bed trying to sleep even with no battery connected, at first i thought that is impossible to have a speaker make sound with no battery power so I must be schizophenic, but then I looked up crystal receiver on Google and found that I had accidently built a crystal receiver which can work with no battery power).
^^Hey, looky here, radio station received with no amplification needed, no battery needed, and no guitar needed

Well do thicker gauge copper wires oxidize slower than thinner gauge copper wires, so that could be a motivation to use a thicker gauge wire for an antenna as well?
 
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(*steve*)

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Oh okay, so the thicker wire gauge for antennas rather than connecting wires is entirely for mechanical purposes.

No, that's just one of many reasons.

The reasons may be:

current carrying capacity
skin effect
mechanical properties
thermal properties
appearance
availability
cost
etc.

It's often hard to know *exactly* why a particular wire gauge was chosen, but it is often easier to understand what might be appropriate.
 

dietermoreno

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Hhm, the skin effect appears to be the most probable cause of relations to radio waves in the list of things you listed.

When I looked up the skin effect on Wikipedia, I found that the resistance of a conductor increases on the outsides as the frequency decreases, which makes a welding rod glow red hot and have a great loss of energy if frequencies higher than mains were to be used.

Here is a table that Wikipedia gave:

Representative parameter data for 24 gauge PIC telephone cable at 21 °C (70 °F).

Frequency. (Hz) ..R (Ω/km)........L (mH/km) G (μS/km) C (nF/km)
1...... .................172.24...... 0.6129...... 0.000....... 51.57......................
1k.................... 172.28....... 0.6125...... 0.072....... 51.57......................
10k........... 172.70....... 0.6099...... 0.531....... 51.57......................
100k ................191.63....... 0.5807...... 3.327....... 51.57.....................
1M............. 463.59....... 0.5062...... 29.111...... 51.57.....................
2M............. 643.14....... 0.4862...... 53.205...... 51.57....................
5M............ 999.41....... 0.4675...... 118.074.... 51.57....................


Then I looked at the Wikipedia article on dummy load.

So I found that in order for transmitters to operate correctly, the minimum load is usually 50 ohms, and this load comes from the resistance of the antenna wire. So these transmitters actually have a greater load to work against considering the skin effect.

So the skin effect would increase the load perceived by the transmitter, as well as increase the load perceived by the receiver.

So the skin effect would dictate that actually the antenna with the least losses would be as thin as possible, correct?
 

davenn

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The schematic that I showed for FM crystal set used uninsulated #18 copper wire for the indoor inductive antenna, but doesn't copper oxidize and isn't that the whole motivation for insulating copper wires (in addition to increase of conduction speed)?

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
 

davenn

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Then I looked at the Wikipedia article on dummy load.

So I found that in order for transmitters to operate correctly, the minimum load is usually 50 ohms, and this load comes from the resistance of the antenna wire. So these transmitters actually have a greater load to work against considering the skin effect.

Yes 50 Ohm is a common value .... now what you are not realising and understanding is that it isnt DC resistance
If you try and measure the DC resistance of a dipole antenna you wont find 50 Ohms or any other value, rather it will be open circuit!!

That 50 Ohms is AC resistance = Impedance and thats a much more complex beast. The skin effect is affected more by frequency than anything else... as freq increases the skin effect ... skin thickness becomes thinner

So the skin effect would increase the load perceived by the transmitter, as well as increase the load perceived by the receiver.
So the skin effect would dictate that actually the antenna with the least losses would be as thin as possible, correct?

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

Dave
 
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CDRIVE

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When I think that your posts can't get any more off the wall you manage to once again raise the bar another notch. 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. That said I'm having a hard time swallowing your speaker story. Was your home a tower house sitting in the 50KW RF field?

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 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.

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.

Last note: Please don't post "Inductive Antenna" again.... EVER!!

Chris
 

dietermoreno

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. 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.
 
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BobK

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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.

Nerve condution is not electrical conduction. It is a chemical process in which the permeability of the nerve to ions changes and this propagates down the nerver fiber. And this travels way slower than the speed of light, a max of about 120 m/sec. Compare to 3x10^8 m/sec for light or electrical signals.

Bob
 

davenn

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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.

You didnt really read what I told you, did you ?
go back and reread my post

Dave
 

dietermoreno

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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

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

Dave

Isn't conduction speed the same thing as propogation velocity?

Well I actually didn't know until now that nerves don't use electricity. All those years of lies told to me by my teachers. I even was starting to think that a good experiment to try would be to take a dead rat in my house and disect it and take out its brain and use its light matter and dark matter to make a PNP transistor, with the assumption that light matter of the brain is a semi conductor that is a different type of semi conductor than dark matter. When I told my biology professor about my idea for this experiment, he even told me that I am correct and the brain is essentialy billions of PNP transistors! All of the lies!

Maybe that shows that you shouldn't ask a biology professor how to build a transistor.

(Perhaps the same could be said for myself that it isn't a good idea to ask a biology major student to build a radio, or else you might end up with a radio with a guitar in it.:D)


Hhm, so a fine coating of copper oxide on a wire is still acceptable for a conductor, most likely I was doing something catestropically wrong when I connected my home made speaker to my speaker output jack of my guitar amp attempting to amplify the radio waves, since I thought, "hey it says speaker jack, so since it says speaker jack that means that radio speaking speaker connects there". Most likely demagnetized the wire and core with the 15 watt output of the guitar amp speaker output from having many shorts from my self-wound coils overlapping. Yes that is how many years I have associated radio receiving with guitars, since I took something familiar to me, guitar, and attempted to apply it to something unfamiliar, radio receiving, with funny if not catestrophic results.

Hey, well at least I don't try to connect my guitar to my guitar amp speaker output anymore and wonder why the guitar isn't playing music (I didn't believe my high school physics text book when it said that guitars use coils similar to speakers, so I wanted to see if guitar would work as speaker). Maybee I should have believed my high school physics text book and not try to make things do things they're not suppose to do.

but I have got a dynamic mic to work as a speaker, but not very well because dynamic mics only are designed to have the cartridge oscillate at human voice frequencies (to about 2000 Hz), and due to the small size of the mic speaker it is not large enough to effectively reproduce bass and it doesn't effectively reproduce trebel either. Pretty much all the dynamic mic speaker can handle is human voice frequencies. It sounds quiet for music, but it fills the room with volume for voices from an AM news station audio source, showing that it only works okay as a speaker for human voice frequencies.
 
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CDRIVE

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I suggest that you Google "Antenna Theory & Design". While you're at it Google "Transmission Line Theory". They should keep you busy for quite some time.

Chris
 

dietermoreno

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I suggest that you Google "Antenna Theory & Design". While you're at it Google "Transmission Line Theory". They should keep you busy for quite some time.

Chris


Okay sounds good. I won't come back to this thread until after I have read tutorials found on Google and watched tutorials on YouTube.

I think I am in need of some basic theory that my high school physics class and even college physics class failed to provide me with.
 

BobK

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Nerves DO operatate electrically, but not by charge flowing along a conductor. They operate by ions moving through the membrane of the nerve fiber. The propagation is more like a sound wave in that what is propagating is a change in physical characteristic (ion permeability) along the fiber If you start the ion flow on one end of the nerve fiber (via an electric potential) then the next cells in line start flowing and the pulse moves like a wave. And an electric potential develops on the other end of the fiber.

Bob
 

dietermoreno

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Hey I have an even better idea than using a guitar amp to see if the antenna works, how about using a ...drum roll...radio receiver.

A clock radio for $5 from the second hand store can be used to test if the antenna works by simply connecting my antenna to the antenna wire hanging out the back of the clock radio.

Also, since the clock radio only costs $5, it is expendable to use as the audio amp with no load connected to it for the audio loop experiment. To use as audio amp with no load connected to it, I take some scissors and clip the leads to the speakers on the clock radio and reconnect the speaker leads to a 1/4 inch jack which can connect to a 30 foot long 1/4 inch cable encircling the room. Then went I want the speakers to work again, I have already stripped the wires and used alligator clips to connect the speaker leads to the 1/4 inch jack, so then I simply connect the alligator clips to the speakers instead of to the 1/4 inch jack.

If only I had thought of that before destroying an amplifier that might not be cheap to repair.

Well I already have a fancy Grundig LW/ MW/ SW/ FM radio receiver, but I don't want to mess with it because it cost my grandpa alot of money, probably worth near $1000 today. So that's why I will use the $5 clock radio for testing instead.
 
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BobK

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Yep. If you are going to destroy, destroy cheap!

Bob
 

CDRIVE

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Yeah, that works for me too. If you're going to make smoke it may as well be cheap smoke.

Chris
 
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