Variable inductor instead of varible capacitor in FM crystal set

[dietermoreno]

Do you own a DMM? Most have a Capacitance function.

Chris

I'm sorry, but I don't what a DMM is. When I Googled the term all I found was "domestic mail manual", and I don't think that's what you had in mind.

 

[CDRIVE]

DMM: "Digital Multi Meter".

http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html

Chris

 

[dietermoreno]

I have an analog muliti-meter.

 

[CDRIVE]

There's nothing wrong with an analog meter but it's not likely to have a capacitance function.

Chris

 

[Mongrel Shark]

I have seen home made crystal radio sets that work with variable inductors. (Can provide youtube video link for how to video upon request) They mostly have variable caps too though.

I also have a video where I make Variable Capacitors from Plastic cups and tin foil. Two cups and two pieces of foil can give a 0-200(ish)pf range. Add more cups and some turn stoppers for greater range. They feature fine adjustment. One model I made (in about an hour) has 560pf of range over 720 deg of rotation.

Here is my video on how I made mine.

I cant see why a variable inductor wouldn't work on frequency's other than AM, but I'm no radio expert either. The sets I have seen are of a school project grade.

Just out of curiosity, did you see my video on google search when you looked for DIY variable capacitors? Comes up on the first page for me, but I think that may be because Google knows its my video....

 

[dietermoreno]

Nope, I didn't see your video on Google search results when I Googled "how to make variable capacitor".

 

[Mongrel Shark]

Thanks for the feedback

I'll go add more tags to the video. Which I made after having exactly the same problem, of not being able to find out how make a capacitor for high voltage. Turns out its so simple a lot of old hands would never need to look it up. All you need is conductor separated by di-eletric (insulator). The larger the surface area of the conductors, the more farads. the thinner the di-eletric the more farads. Due to columb force saturating the neg plate with more electrons, which in turn repels electrons from the pos plate. Kitchen cling wrap is a good alternative from cups. Especially for lower voltages. The cups are good for 50kv Except the ones with welding rod stoppers, the stoppers start arcing like a stun gun at about 30kv

Paper is a good di-eletric at 9v or less. Use your imagination Soda can's are a great resource for this kind of stuff too. Bit more sturdy than foil. Just be sure to sand off the plastic coating. Just be careful with aluminum and salt water (or any water) as it makes a great battery Google "Aluminum air battery". If you get negative capacitance, and there is water near you ally, thats probably whats going on.


Did you find my video helpful? (it get 100 hits a week, but I get very little feedback, Guess thats a good thing.) Are you still interested in trying with a variable inductor? I think it will work just fine. Radio reception is all about the resonant freq in a tank circuit, and the inductor is a critical part of that tank circuit. Change its vale and you change the freq. My main concern would be corrosion on the brush or whatever contact point you chose. Copper oxide makes a handy semi-conductor at times. Less handy when you dont want it though. Leaves you constantly moving the connection around as the connection becomes intermittent the longer you leave the oxide undisturbed.

Here is Another video, with a variable inductor and variable cap crystal radio. Its not by me, but I can recommend the Chanel. Lots of excellent electronics and science projects that can be made without soldering anything. As well as being open source and non-profit.

Here's how to make it:

and here is how it works, at an electron level(with animations).

 

[dietermoreno]

Oh, your trying to make a high voltage capacitor.

I don't think that's applicable to what I'm doing, because what I'm doing is trying to make a simple variable capacitor that will work for both AM (MW) and FM (VHF) radio reception.

I might be wrong, please correct me if I'm wrong.

Well actually, on another thread yesterday I was told by CDDrive that the reason that VHF circuits have to use as short wires as possible is that any extra wire length will make the circuit resonate at a frequency lower than it is supposed to. but I guess that is another problem with taps that they oxidize and create unintentional rectifiers.

I will definitately watch the YouTube video and the channel link you gave to solderless circuits!

Thanks!


Anyway, I found that a variable capacitor for VHF is much easier to build than it looks. I just used old plastic loyalty cards and aluminum foil to cut out rotor and stator plates and I pounded nails through the plates to mount them together and allow the rotors to rotate while the stators are stationary.

I haven't completed building my variable capacitor yet, but I'll let you know if it works, and if it works I'll record a video of it in action!

 

[davenn]

I don't think that's applicable to what I'm doing, because what I'm doing is trying to make a simple variable capacitor that will work for both AM (MW) and FM (VHF) radio reception

You wont make a variable capacitor for VHF in the style you were doing for AM broadcast
The VHF one will need very small plates very close together else it will have too much capacitance and wont work in the tuned circuit

and speaking of tuned circuits.....

The drawings you did are not tuned circuits .... the variable capacitor should be in parallel with the inductor NOT in series with it.
I really wish you would stop playing with those curcuits you are drawing and use a correct receiver circuit
You have been shown some and there are many more available on the net

if you want to build a radio then do it properly, you will have success and much more learning enjoyment

Dave

 

[Mongrel Shark]

A high voltage cap will work fine at lower voltage. The fine adjustment sensitivity of my cup-caps would make them ideal for higher freq adjustment. With a little creativity with plate shape, you can make them as sensitive to adjustment as you like. Try a small square or rectangle plate and a triangle plate, with a very long taper.

Having read Davenn's comments, I concur about making one that is proven first. then you can play around and actually know what you are doing. Davenn does know his radio stuff. If he says it has no hope, I'd be inclined to listen.

I don't pretend to know enough about radio to waste my time reviewing your circuit. when I would have no idea if it would work or not work or why that may be, but even I know the tuning cap goes in parallel with the inductor.

I'd recommend you find some good info on "Tank Circuits" Preferably an animated one, at the electron level. Its not as complex as it sounds once you can visualize the electrons.

ok. I just looked at the circuit you posted.... You need help.... Go build rimstars crystal set, its almost the same, but will actually work. Pay special attention to his variable inductor. I'm not going to wast my time listing the 27 things I see wrong with yours. Its too thick, too short and has terrible adjustment, just to pick the top three issues. I'm also guessing you mean dual core speaker wire. which means it may be bifilar and actually be a capacitor half the time... No I'm not wasting my time....

If you get the Rimstar set to work, then look at the difference in freq from AM to VHF, and look at how sensitive the am tuning is. Then consider how much finer it will have to be to work on VHF. There is no way your going to get a VHF to work as your first radio. Unless your an electronics genius, but if you where, you would not need help from this forum.

K.I.S.S. Keep It Simple Stupid. The number one rule of the self taught engineer.

 

[Mongrel Shark]

Also, This is more a question for the Radio guy, that have actually built working radios.

Wouldn't a de-coder of some kind be needed to pick up VHF? I was under the impression its mostly encrypted or side band? Ie not something your going to tune into with a crystal set. I see the op is in USA, is there unscrambled VHF or UHF there? I'd be surprised to find it in Australia now the VHF tv network is being shut down...

 

[davenn]

Love your signature MS ...

If you can't fix it with Gaffa Tape and Tie wire, It's broken. You need a new one.

the true DIY'ers philosophy

Dave

 

[dietermoreno]

Also, This is more a question for the Radio guy, that have actually built working radios.

Wouldn't a de-coder of some kind be needed to pick up VHF? I was under the impression its mostly encrypted or side band? Ie not something your going to tune into with a crystal set. I see the op is in USA, is there unscrambled VHF or UHF there? I'd be surprised to find it in Australia now the VHF tv network is being shut down...

I hear FM radio on my guitar lol.

So yeah, in America FM is still analog. I don't know about Australia. The analog VHF TV network has been shut down in America since 2009.




I am watching RimStar's video right now, and I see that he used magnet wire instead of speaker wire so its cheaper! 200 feet for only $5!

You wont make a variable capacitor for VHF in the style you were doing for AM broadcast
The VHF one will need very small plates very close together else it will have too much capacitance and wont work in the tuned circuit

and speaking of tuned circuits.....

The drawings you did are not tuned circuits .... the variable capacitor should be in parallel with the inductor NOT in series with it.
I really wish you would stop playing with those curcuits you are drawing and use a correct receiver circuit
You have been shown some and there are many more available on the net

if you want to build a radio then do it properly, you will have success and much more learning enjoyment

Oh, I guess there is a good reason for the inductor being in parallel with the variable capacitor instead of in series, and I should not "just try things" if I don't understand why it needs to be that way. (Well if I tried to do that, presumably it wouldn't work, but I don't know yet and I won't try to build it that way because that would be a waste of my time if you say it won't work because your the expert davenn.)

I still don't understand why the circuit has to be that way or it won't work, so yeah I'll look up what is happening in tank circuits on the electron level.

Edit: RimStar's channel had an animated video with tank circuit on the electron level! I watched it, and now I know why its called a tank circuit!

Say we call electrons water molecules and we call electric current water current. Say we have a garden hose coiled. When you increase the number of coils on the garden hose, make the hose longer, and or make the coils have a wider diameter, it impedes the flow of water current greater. That is all it does, impede. An inductor in series with a capacitor is not a tank circuit, the inductor is acting as a resistor. Now say we connected a water bucket to the hose with the hose at the bottom of the bucket and the hose is hanging down from the bucket so gravity draws the water molecules down the hose. Now say we connect a bucket at equal height as the other bucket. The water sloshes back and forth between the two buckets, and the more coils to impede the water molecules, the lower the oscilation of the sloshing. The "gravity" in electric tank circuit is ground! It won't do anything without ground! The alternating current "wants" to go to ground, in the same way that the water molecules are pulled down by gravity. No gravity, and the water tank circuit doesn't do anything. No ground, and the electric tank circuit doesn't do anything.

So, my current images that I posted of my schematics that I drew, those all have the inductor acting as a resistor and the capacitor has capacitative reactance just like DC resistance, so if anything, all those circuits would do is make the radio waves quieter, rather than louder.


RimStar even explained what the 100k resistor in the crystal receiver does! No one ever explains what that does. So remember that we have a tank circuit. Now think what if the water tank circuit had a valve that would only let water flow one way. All oscillation ceases, unless the valve is leaky. Diodes can be "leaky", but that is not intentional.

There has to be a bypass around the valve that will allow the water molecules to flow past the valve so that oscillation of the water tank circuit will continue. Unfortunately, with a simple bypass all that will accomplish is the water molecules will go half in each hose. We can prevent this from happening and have more water molecules go into one hoe rather than another by adding a thin hose that moves water molecules through it slowly.

There has to be a bypass circuit around the diode that will allow the electrons to flow past the diode so that the oscillation of the electric tank circuit will continue. Unfortunately, with a simple bypass all that will accomplish is the electrons will go half in each wire. We can prevent this from happening and have more electrons go into one wire rather than another by adding a resistor that moves electrons through it slowly.

The diode must be strategically placed in this circuit so that the above conditions are met. I don't know how to explain it in words, so I drew a picture (attached). You can not just randomly put the diode where the phones are shown in my attachment. If you do that, all you have done is build a circuit to anttenuate any received radio signals. Therefore, you can not just connect a coil and antenna to an output jack and connect the output jack to a Hi-Z guitar amp input jack and call that a tuned circuit; it isn't a tuned circuit, if anything it is attenuated.

The bucket stores water molecules. Making the bucket smaller means it stores less water molecules, so that means that less water molecules can flow through the coils faster so the oscillation happens faster.

The variable capacitor stores electrons. Making the variable capacitor smaller means it stores less electrons, so that means that less electrons can flow through the coils faster so the oscillation happens faster.

Now that I understand this stuff at the electron level, it makes me almost have a nuclear meltdown when while I was doing my calculus homework in the library today I heard a group of physics students saying the phrase "current flows" about every 10 seconds. A river current is not what is moving, the water molecules are what is moving. Similarly, an electric current is not what is moving, the electrons are what is moving.

That's why I never understood what the 100K resistor does and never understood why I can't use my guitar amp as the semi conductor in a tuned circuit, because I kept thinking of the phrase "current flows"! All the lies the physics professors are teaching at my school!

 

[Mongrel Shark]

So, my current images that I posted of my schematics that I drew, those all have the inductor acting as a resistor and the capacitor has capacitative reactance just like DC resistance, so if anything, all those circuits would do is make the radio waves quieter, rather than louder

Yep. Now your starting to get it Although there are a number of other problems too. I can see multiple issues with just about every part....

For example, the thickness of your wire is like using a very large fire hose in your bucket example.... I don't know exactly how its going to mess with the circuit, but it will. That is another reason rimstar uses thin wire. I could be wrong here, but if I wanted to get MHZ range (think about that for a moment. Millions of oscillations per second. Thats really really fast! oscillation's every few nano seconds!) Id be reaching for thin wire for lower inductance. A quick check of the induction of 2 different 3 inch nail's validates me. I got a higher reading from the thicker one.

and I should not "just try things" if I don't understand why it needs to be that way.

Just try stuff. Its a great way to learn. I teach myself stuff that way daily. Just dont expect it to work every time. Like I just did with 2 nails and an induction meter. Worked, learned something. Or the time I tried to make a FET with a spark gap in a cup-cap. It didn't work out exactly how I wanted, I got an electrically adjustable spark gap, I also set a few cup-caps on fire... Failed, but I learned stuff from the failure, and gained a better understanding for next time. There are a few do's and Don'ts though.

Do have some inkling what you are doing. If you throw random parts together in a random fashion, it will either work or not work. Either way you will have no idea why and learn nothing. This is why scientist tend to play with only one variable at a time. As well as fully understanding a "Control" which in this case would be a simple crystal set.

Do ask for help if you get stuck, But Don't expect someone else to fix every part of a circuit for you. Which is sort of what you are doing here. Inventing your own parts is for after you got one working. If you never made one before, and need to use home made parts. Find someone thats done it before, with sucsess, and copy that first. You will learn stuff. Then you will have a much better idea why the parts you are inventing are not working.

Don't just assemble random parts, unless you have some idea what the results will be. No one will help you. I tried that once too. Got a similar response to you. Now I know a bit more, I can see why. Its like trying to teach someone to read, when they only know half the alphabet.

Do do some homework, we can help, but not teach you from scratch, there are tons of great resources online that can do that better anyway. Like rimstars channel, and many many other sites.

Do look at what others have done before you. You will learn stuff.


Don't get testy with people that are donating their time to help you. We don't have to help. We dont get paid, or any other benefit, other than a warm fuzzy feeling. If you don't listen we wont have time. Sometimes its hard to convey full meaning without facial expression or voice tone. Thats what the emotes are for. "You stink", is very different to "you stink " which is clearly a jest.

Do be able to measure stuff well. If your going to self teach, I recommend some decent meters. Or even better learn to make and calibrate your own. My first lesson in electronics, from my Uncle, was whats inside a multimeter and why its there, what it does... Analog is best for this. Its all you need. There are guides online for making a cap meter or induction meter. You can also get some half decent ones on ebay for really cheap.


Don't let frustration beat you. Its going to happen, regularly at first. Take a break, do other stuff. go for a walk. Come back to it later and something obvious will likely jump out at you. Failing that study working ones, with proven design and see whats different. As Davenn and a few others have suggested

Don't use foil for a fuse. Steve will ban you I've done it, half the people on the forum may have at some time, but we dont talk about it in public. Thats a great way to get sued. (*Disclaimer* I personally recommend inline fuses on all projects) 3 inch nails and bolts are not fuse's ether.

Do use proper circuit symbols when possible. Its horribly confusing if you dont. Also consider, you had me trawling through google images trying to work out what component that was... I'm still learning a lot of switching components....


I think your should be getting the point by now. I wont go on.

Go make the rimstar model. then when you have that working. You can do the maths to work out how much you need to change values for your parts. Then, if you still think it will work. and you can make parts that sensitive. give it a go, and people here will be much nicer to you. But we cant teach you to read write and spell well, until you learn your ABC's so to speak. Really we'd rather just help you with a single thing at a time. You just turned up to a how to speak english room, and asked us to help decipher the Koran. Except your copy is a cheap knock off, and has the pages in the wrong order.... We are all going nowhere, fast.





Also, Davenn. Zip ties are the new tie wire, and I just got this fangled contraption, called Spray adhesive What will they think of next?

 

[dietermoreno]

Yep. Now your starting to get it Although there are a number of other problems too. I can see multiple issues with just about every part....

For example, the thickness of your wire is like using a very large fire hose in your bucket example.... I don't know exactly how its going to mess with the circuit, but it will. That is another reason rimstar uses thin wire. I could be wrong here, but if I wanted to get MHZ range (think about that for a moment. Millions of oscillations per second. Thats really really fast! oscillation's every few nano seconds!) Id be reaching for thin wire for lower inductance. A quick check of the induction of 2 different 3 inch nail's validates me. I got a higher reading from the thicker one.

That makes sense. If you connect a fire hose to a garden hose water spout, the water molecules will move much slower. So the thicker the wire gauge, the slower the oscillatory frequency.

Just try stuff. Its a great way to learn. I teach myself stuff that way daily. Just dont expect it to work every time. Like I just did with 2 nails and an induction meter. Worked, learned something. Or the time I tried to make a FET with a spark gap in a cup-cap. It didn't work out exactly how I wanted, I got an electrically adjustable spark gap, I also set a few cup-caps on fire... Failed, but I learned stuff from the failure, and gained a better understanding for next time. There are a few do's and Don'ts though.

Okay.

Do have some inkling what you are doing. If you throw random parts together in a random fashion, it will either work or not work. Either way you will have no idea why and learn nothing. This is why scientist tend to play with only one variable at a time. As well as fully understanding a "Control" which in this case would be a simple crystal set.

Oh I think I get it! The control is the simple MW crystal set, and improvements on it are the variables.

Do ask for help if you get stuck, But Don't expect someone else to fix every part of a circuit for you. Which is sort of what you are doing here. Inventing your own parts is for after you got one working. If you never made one before, and need to use home made parts. Find someone thats done it before, with sucsess, and copy that first. You will learn stuff. Then you will have a much better idea why the parts you are inventing are not working.

Okay, so if my home made part has a different design from a home made part that some one else built, it would be good to have a way to measure the inductance or capacitance and then use some simple maths to calculate the resonant frequency.

Don't just assemble random parts, unless you have some idea what the results will be. No one will help you. I tried that once too. Got a similar response to you. Now I know a bit more, I can see why. Its like trying to teach someone to read, when they only know half the alphabet.

Okay.

Do do some homework, we can help, but not teach you from scratch, there are tons of great resources online that can do that better anyway. Like rimstars channel, and many many other sites.

Yeah, I learned more about how inductors, capacitors, resistors, and tank circuits work at the electron level on Rimstar's channel than I ever learned in my physics class.

Do look at what others have done before you. You will learn stuff.

Makes sense. What others have working I should get it working first instead of making stuff up.

Don't get testy with people that are donating their time to help you. We don't have to help. We dont get paid, or any other benefit, other than a warm fuzzy feeling. If you don't listen we wont have time. Sometimes its hard to convey full meaning without facial expression or voice tone. Thats what the emotes are for. "You stink", is very different to "you stink " which is clearly a jest.

Makes sense.

Do be able to measure stuff well. If your going to self teach, I recommend some decent meters. Or even better learn to make and calibrate your own. My first lesson in electronics, from my Uncle, was whats inside a multimeter and why its there, what it does... Analog is best for this. Its all you need. There are guides online for making a cap meter or induction meter. You can also get some half decent ones on ebay for really cheap.

I already have an analog multimeter, and it doesn't measure inductance and capacitance, but I can make my own your saying!

Well I read some instructions on how to build home made capacitance meter and its not as easy as I hoped, so I think I will use math to find out the inductance of the coils since the math to find out the inductance of the coils is not that hard, and then when my coils and capacitors allow me to tune to a station, when I know the station's frequency and I know the inductance of the coils I can solve for the value of the capacitor.

Don't let frustration beat you. Its going to happen, regularly at first. Take a break, do other stuff. go for a walk. Come back to it later and something obvious will likely jump out at you. Failing that study working ones, with proven design and see whats different. As Davenn and a few others have suggested

Okay.

Don't use foil for a fuse. Steve will ban you I've done it, half the people on the forum may have at some time, but we dont talk about it in public. Thats a great way to get sued. (*Disclaimer* I personally recommend inline fuses on all projects) 3 inch nails and bolts are not fuse's ether.

Okay.

Do use proper circuit symbols when possible. Its horribly confusing if you dont. Also consider, you had me trawling through google images trying to work out what component that was... I'm still learning a lot of switching components....

Okay.

I think your should be getting the point by now. I wont go on.

Okay I think I'm getting it!

Go make the rimstar model. then when you have that working. You can do the maths to work out how much you need to change values for your parts. Then, if you still think it will work. and you can make parts that sensitive. give it a go, and people here will be much nicer to you. But we cant teach you to read write and spell well, until you learn your ABC's so to speak. Really we'd rather just help you with a single thing at a time. You just turned up to a how to speak english room, and asked us to help decipher the Koran. Except your copy is a cheap knock off, and has the pages in the wrong order.... We are all going nowhere, fast.

Okay, I'll go make the RimStar model, EXACTLY as he made it, to guarantee that it will work, and after I have it working, I can try different combinations of inductors and capacitors to see what works.

I was worried that I would be too clumsy the wind all the coils on such a small coil form, but RimStar makes it easy with the masking tape technique! I assume that duck tape wouldn't work for this, because duck tape leaves too much residue, so I have to buy masking tape.



Calculations for air core inductor:

, where L is the inductance in Henries, l is the length in meters, A is the cross sectional area in meters squared, N is the number of turns, and mu is the relative permiability constant of air.

The relative permiability constant of a vacuum is 1. The relative permiability constant of air is 1.00000037

RimStar's first coil has 90 turns around a toliet paper roll of about 3.5 inch diameter and length of about 5 inches long.

The area of a circle is pi*(r squared).

Half the diameter is the radius. So the radius is 1.75 inch. We must convert the distances into meters. I used an online converter.
1.75 inch = 0.044450m 5 inch = 0.12700m

Once you find the inductance for one coil, you multiply it by (N squared).

The cross sectional area of one coil if it was the whole length of the toliet paper roll therefore is (1.00000037 )(1) [ pi * (0.044450m squared) )/ (0.12700m) ] = 0.048875 Henries

1 micro Henry= 1.0E-6

0.048875 Henries / 1.0E-6 = 48,875 micro henries

I found a website selling AM antenna ferrite loop sticks that have about 680 micro henries.

So I think I did something wrong in my calculations.

I think I found the problem. The length is supposed to be for each coil, not the length of the inductor.

So it appears that if I used a moving box to wind 20 coils on, that would be WAY TOO MUCH inductance.

Well so I will say that each coil has length of the toliet paper roll divided by number of coils, assuming that coils are evenly spaced.
So that gives a length per coil of 0.12700m/ 90 = 0.001411 m

So I will try the equation again with the new length. (1.00000037 )(1) [ pi * (0.044450m squared) )/ (0.001411m) ] = 4.399 henries
That's an even less reasonable answer!

Oh, I think I know the problem, my equation is approaching dividing by zero and that has some strange things happen... It has infinite inductance from an inductor that has a coil length size approaching 0. A number divided by a value approaching zero will lead the result to approach infinity.

The cause of the approaching dividing by zero is that my coil length is too small. So the equation must mean THE LENGTH OF THE WIRE IN EACH TURN, rather than the actual physical space that each coil takes up in length on the paper towel roll up and down on the roll.

The length of the wire in each turn, assuming no coil spacing, is the circumference of the coil.

Circumference of a circle = 2*pi*r

Circumference of RimStar's inductor for each coil = 2*pi* 0.044450m=.27928 (m^2)

So now the inductance of each RimStar coil is (1.00000037 )(1) [ pi * (0.044450m squared) )/ (.27928) ] = 0.022305 henries

0.022305 henries / 1.0E-6 = 22, 305 micro Henries per coil.

Still too much!

Wait, I think I used the wrong permiability constant. I think I was supposed to use the permiability constant instead of the relative permiability constant.

So now the inductance of each RimStar coil is (1.2566375E −6)(1) [ pi * (0.044450m squared) )/ (.27928) ] = 2.8029 E -8 henries

2.8029 E -8 henries / 1.0 E -6 = 0.028029 micro henries

That's more like it!

(0.028029 micro henries)*(90 turns)=2.52269 micro henries

The ferrite loop stick has a multiplier of about 10-100 for the ferrite core. So (2.52269 micro henries) (100) = 252.269 micro henries.

So therefore, the 680 micro henry ferrite loopstick has turns found by solving this equation:

252.269 micro henries / 90 turns = 680 micro henries / x turns

252.269 x = 90*680

252.269 x = 61,200

x = 61,200 / 252.269

x = 242.5 turns


So since the inductance on RimStar's inductor is not that much compared to the ferrite loopstick, that's why he must use such a large variable capacitor. Compared to an AM/FM radio can use the same variable capacitor as long as the AM ferrite loopstick has enough inductance.

Well so after I get RimStar's crystal set to work, I could increase the inductance of the inductor to allow a smaller variable capacitor to be used by placing a big iron bolt inside the toliet paper roll.

I think a steel rod from an unused steel cymbol stand will work.




Time to start ordering parts!

So since I'm using magnet wire, I should order sand paper to sand off the enamel at the connections.

RimStar's crystal set doesn't even use alligator jumpers, and just uses magnet wire with sanded off enamel at the connections and masking tape to hold the connections together so its cheaper!

So I don't need to buy alligator jumpers.

So all I need to buy is magnet wire, masking tape, and sand paper.


The ill:

sandpaper $1.75 http://www.amazon.com/3M-Aluminum-S...ref=lh_ni_t?ie=UTF8&psc=1&smid=A2BBUA7LL95L5R

masking tape $1.37 http://www.amazon.com/Office-Impres...ref=lh_ni_t?ie=UTF8&psc=1&smid=A1RDYXN1JW1DJR

magnet wire #22 AWG $7.90 http://www.amazon.com/22AWG-Solid-I...id=1367946139&sr=1-1&keywords=magnet+wire+#22

Also included guitar output jack for $1.95

total before shipping and handling: $13.41

total after shipping and handling: $28.03


On second thought, I'll just buy as much as I can from the local hardware store except the guitar output jack so I don't have to pay for shipping and handling.



On third thought (if that's even a word), I'll buy the sand paper and masking tape this week, buy the magnet wire next week, and buy the amplified PC speaker from the second hand store to steal semi conductors from on the week after that. This is so that my weekly allowance that my dad gives me is sufficient without having to ask for more until I get summer job.



On fourth thought (if that's even a word), I already bought the sand paper and masking tape today, and if I build a fox hole version of the RimStar crystal set I don't even need to buy a diode, resistor, transistor, or guitar output jack, so the only thing left to buy is the magnet wire for $5.

As the diode I would be using a blued razor blade (already have an old dirty rusty razor blade, I just need to blue it in the gas stove in the kitchen) connected to a half inch long piece of mechanical pencil lead as the point contact rectifier.

As the resistor I would be using an inch long piece of mechanical pencil lead.

As the output jack, the output wire leads are connected to a guitar cable with masking tape. The ground wire is connected with masking tape to the ground (outer part) of the cable jack. The hot wire is connected with masking tape and a single tiny alligator clip to the exposed hot wire on the inside of the cable by unscrewing the plug off of the cable enough to expose the hot wire. Just need to buy a few tiny alligator clips for a dollar.

 

[Mongrel Shark]

That makes sense. If you connect a fire hose to a garden hose water spout, the water molecules will move much slower. So the thicker the wire gauge, the slower the oscillatory frequency.

Not really, but closer than you where before.
If your going to visulise a hose system. Try air instead of water. it behaves much more like electricity. A battery would be a compressor tank, and a charger the compressor. resistors are narrow points, at which the air gets a little compressed and makes wastes a bit of energy as heat. All the wires in a circuit are inductors and resistors. Its just that the values are mostly very low. Inductors are stretchy hoses. The faster the airflow. the more they stretch out, holding air at pressure. If you close the valve that connects the hose to the pressure tank, the hose shrinks back to its natural size and continues to push air out after the inlet tap is closed. You can try this with a garden hose and tap too if you have a good spray nozzle and pop fit fittings. turn the hose on, close the spray nozzle, so no water comes out the hose. The hose stretches to take mains pressure. now got turn the wall tap off, and un-clip the hose from the turned off tap nozzle.... You will get a blast of water in the face from the pressure stored in the hose...

Except in electronics. the wire doesn't stretch, it gets a magnetic field around it, which consumes energy to be created (Like ah hose stretching) then when current stops flowing, the field collapses. giving you back the amount of power consumed when it was created. Except there is often no where for the current to flow, so it gets forced to turn into voltage, to lower the effective resistance of stuff to it, and find an escape. Often as a high voltage spike, that can make smoke come out of stuff if your not careful.

Oh I think I get it! The control is the simple MW crystal set, and improvements on it are the variables.

You need a working one before you can make a better (or worse ) one.

Okay, so if my home made part has a different design from a home made part that some one else built, it would be good to have a way to measure the inductance or capacitance and then use some simple maths to calculate the resonant frequency.

Home made parts of unknown value, are total randoms. if it work or not, you will have no idea why and not be learning, you will likely get confused and make wrong guesses. teaching yourself something that is misguided or false. Also if you cant measure anything, how would you replicate, or explain it to someone. This is when we get fussy with symbols and stuff. Rimstar might use a certain gauge for example, but I dont have that, but I do have one close (or even miles out) if I know the values I can still replicate to some extent. As well as make informed modification should I need, to change the freq or volume or whatever I like. I can also build it in a simulator and see how it looks there. I like this one, Which you can download too. It has some great lessons too. check out the circuits list. www.falstad.com/circuit/‎

Well I read some instructions on how to build home made capacitance meter and its not as easy as I hoped, so I think I will use math to find out the inductance of the coils since the math to find out the inductance of the coils is not that hard, and then when my coils and capacitors allow me to tune to a station, when I know the station's frequency and I know the inductance of the coils I can solve for the value of the capacitor.

I didn't say it would be easy to make just that you can (If you learn well) Your on exactly the right path. Learn the maths till its second nature (when you get that good, go back to your circuit drawing, and you will have quite a laugh ) You can also get cheap ones on ebay I have one of these http://www.ebay.com.au/itm/LCR-RCL-...Electrical_Test_Equipment&hash=item1e71b8d5cf Which I paid $7.50 for. and a cheaper one that has no resistance range. They are reasonably acurate, good for crustal sets and power suplys. Probably not so good for vhf.. I also have this one http://www.ebay.com.au/itm/High-pre...Electrical_Test_Equipment&hash=item4609b066f6, which comes in many models with diferent ranges. Pretty sure mine goes to 10f on the big cap range, as I wanted to be able to measure super caps accurately. Its a quality meter, for the price. Your going to pay well over $100 to get a better one. There are also cheaper ones with reduced ranges. like a $15 one with no hi-L and another with no hi-C... Its good to be able to check your maths against something. There are also a ton of online calculators like this one: http://www.zen22142.zen.co.uk/Theory/tunedcct.htm Do some googling, and find one you like.

Yeah, I learned more about how inductors, capacitors, resistors, and tank circuits work at the electron level on Rimstar's channel than I ever learned in my physics class.

Rimstar is a great teacher, but so are a few hundred others on the net. Look around. google google google.

Okay, I'll go make the RimStar model, EXACTLY as he made it, to guarantee that it will work, and after I have it working, I can try different combinations of inductors and capacitors to see what works.

You will have fun and learn the whole time


I had a quick skim over your maths. Looks like your headed the right way. No one is going to check all your crazy ideas for you so you need to be able to self check. Looks like you got that under control. Comparing to known values and parts and seeing if it all works out. Rimstar will have measured the parts. its likely on his website if not on the video, failing that, just ask, He will respond. Do look at how many people he helps though, and try not to take too much of his time.


My only other suggestion. Don't Buy stuff. Scrap it. I get miles of wire from CRT tv's (You can kill yourself from the energy stored in the tube, do LOTS of homework if you attempt that) I find on the side of the road. I also get a lot of stuff from Freecycle.com and friends that know what I do. The other advantage to all this, is I get to look over the circuit boards, and try and work out what all the parts do. At first it was just a big jumble of parts. now I can tell you what at least half the parts in a TV do. and could work the rest out if I actually wanted to fix one rather than scrap it. I literally have 20 liter buckets full of inductors and caps... As well as an ice cream tub full of 1/8w resistors... which is a pain as its all assorted.... Take my advice and sort stuff as you pull it off, or you get an organizational disaster fast.


Good luck and have fun

 

[dietermoreno]

Hhm, well since scrapping a TV is above my knowledge level, I think I will stick with the $5 magnet wire from the local hardware store.

Yes, in my maths I had quite a laugh at my 20 turns around a moving box that resulted in several henries. Enough inductance for a resonant frequency near audio frequency lol.

Thanks for all of your responses!

Another thing: I should use a nail for the contact to touch the razor blade instead of a pencil graphite stick, because graphite is lossy which is why I am using it for a resistor. I don't think it is intentional in any way that pencil graphite was used in the fox hole radio to connect to the razor blade. I think it had more to do with a safety pin stuck inside a wooden pencil providing mechanical stability and the wood on the outside of the pencil insulated the wire from being grounded by your body, so using mechanical pencil graphite defeats the purpose. As an insulator, I could wrap the nail in masking tape at the part where my finger touches it.

For how I will actually build the wiper blade, it is very similar to the variable capacitor that I built-- in fact its the exact same thing with only one rotor plate and no stator plates. Since the thickness of the plates isn't critical this time since its not a capacitor and only a sliding contact, I can cut out a little rectangle of cardboard from one of my many Amazon boxes, super glue aluminum foil to it, nail two nails through, and mount machine washers on each nail with masking tape to hold the washers so that the washers hold the cardboard steady. One nail is the tuning nail that is for my finger to use to pull the wiper blade across the inductor, the other nail is what holds the cardboard up in the...guess what the substrate is...cardboard from an Amazon box is the substrate.

So until I buy the magnet wire, its time to get to work sanding the paper towel roll for the antenna trimmer capacitor, assembling the antenna trimmer capacitor, sanding the toliet paper roll for the inductor coil form, and assembling the wiper blade sliding contact.

My only concern is the sanded magnet wire oxidizing. The magnet wire has to be sanded to remove its enamel at where the wiper blade touches the coils. I have read that it was a weekly chore back in the crystal days to replace the long wire antenna since the copper wire oxidized to an unusable state once a week. I don't know if the antenna being outside had to do with it oxidizing so fast. Hopefully the coil inside will not oxidize so fast so I won't need to buy new magnet wire anytime soon.

Since my response is so brief here, take that as a good thing that now I know what I'm doing and don't need to ask for help anymore!

 

[Mongrel Shark]

See how you go with the nail diode. May work, I'd make a pencil one too and compare them... A needle would be what I'd be reaching for rather than a nail.. Maybe sharpen Your nail. Sharpened oxidized copper would be another one to try. Most oxides seem to be semiconductor in the right (or wrong) conditions.

I had a feeling the graphite and carbon in the pencil is acting as a semi conductor, as well as the shape of the "Spark Gap" Could be wrong though, Do some comparisons and see what you find.

Re oxidizing copper. I tin my copper so that doesn't happen as fast, and your not removing copper when you sand it, which will eventually wear it out... Tinning will change the inductance. as will sanding the copper thinner. If no soldering yet, then look at conductive glues and contact enhancers. Silver pens for drawing circuit boards, that sort of thing. Lanolin oil would be worth a shot. Dielectric as an air gap, to 70kv, but if contact is made its a contact enhancer. I have no idea how it works, But been using it on ignition points and battery terminal for years, and thats what it does...

A bit of graphite powder for a pencil can help improve contact on the wiper I use it on my potentiometers

 

[dietermoreno]

Okay, so I guess that a safety pin would work better than a nail since it has a smaller contact surface area so it would have more accuracy selecting a sensitive spot on the blued razor lade.

Also, I found another good channel:

From this channel, I learned that a tank circuit is counter intuitive in that it doesn't select a resonant frequency, actually all it does is simply ground frequencies from a higher number of coils than the position that the tap or wiper blade is connected (or for variable capacitor plate area, spacing of plates, and number of plates). So that's why it needs ground, or it won't work. So it is actually a frequency rejector rather than a frequency selector.

From that channel, I also learned that the purpose that the antenna trimmer capacitor serves is to control the capacitance of the antenna with the Earth where the antenna is using the Earth as the plate of a capacitor. So the trimmer capacitor comes before the actual tank circuit if two variable capacitors are used. However, in RimStar's crystal set, there is only one capacitor and he chose to use it as both the trimmer capacitor by coupling it directly to the antenna and as the tank circuit capacitor.


Hhm, I measured the resistance of my 3 inch long mechanical pencil graphite stick after I zeroed the meter by calibrating it to zero when the meter leads are touching each other, and the resistance value of the graphite stick at the maximum distance between each meter lead was only about 10 ohms. So I don't think the graphite stick will do as the 100 K resistor. I think if I drawn a line on paper with the pencil I can make a resistor like that, I've seen it done on YouTube videos before.



Well I'm bored waiting a week for more money to buy the magnet wire so that my dad doesn't notice me taking money out of my allowance money account, so I think I can use a single coil guitar pickup from my nasty sounding single coil guitar as the coils just for fun not expecting it to work until I buy the magnet wire. And for the connection wires until I buy the magnet wire I can build my own wires out of aluminum foil wrapped with duck tape as the insulator! I wonder if Mr. Fender knew that his single coil pickups worked as components in fox hole radios...I wonder why he didn't just go to humbucker pickups immediately after the 50 years of radio technology that proceeded his guitar. I wonder if I am the first person to attempt to attach a variable capacitor, antenna, and crystal detector to a single coil pickup guitar; I doubt I'm the first.


Without even using a variable capacitor, antenna, or crystal detector, attached is an image of what my single coil guitar picks up. My ears can only hear mains hum, but you will see in the image that there is much more hidden in the carrier wave waiting to be rectified with a crystal detector! My ears don't hear the audio because the audio cancels out since both waves are the same opposite of each other.


In fact, this image is so promissing since it looks just like RimStar's animations of amplitude modulation, I think my first experiment will be simply connecting the guitar output jack to my crystal detector and listening to what I pickup, in addition to the recording will allow me to see in the software if the crystal detector is working. If the crystal detector is working, only one half of the radio waves should remain showing up in Audacity on the screen.

 

[Mongrel Shark]

You can get wire from transformers too.


I dont know how you will go with the guitar. I think you'll end up going for a proven model before thats going to work. Good luck though