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Offline GarrettManRPTopic starter
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« on: June 15, 2020, 06:56:58 pm »
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Are Silver Mica capacitors still a decent choice for capacitors in oscillator tank circuits due to their stability and low loss characteristics? Or have other types surpassed them now? And were they only for high frequency applications or do they function well at VLF frequencies too? Letís say VLF = 10 khz to 50 khz.

I am experimenting with a high efficiency tank circuit. I am building a spiderweb coil with Litz and Iím looking for a good cap to compliment it in a tank.




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« Last Edit: June 15, 2020, 07:54:31 pm by GarrettManRP »
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« Reply #1 on: June 15, 2020, 11:56:56 pm »
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don't laugh , i'm just learning , why don't put a cristal instead a capacitor that is more stable than a tantal ?

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« Reply #2 on: June 16, 2020, 07:33:38 am »
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I should have been more clear. Iím working with an LC circuit. When I mentioned stability I was referring mainly to temperature stability and capacitance stability over the life of the device.
Metal detectors have need for both stable and not so stable circuitry with respect to oscillation. In this case Iím working on a search coil oscillator and I want the frequency to change when nearby metal changes the inductance of the coil so this is an LC circuit. A crystal would not serve me here I donít think.
Silver Mica caps are I believe also known for low parasitics a.k.a low resistance and low inductance which is a good thing if you want efficiency in a tank circuit capacitor.
Spiderweb coils also have low parasitics serving as an efficient coil for a LC tank circuit.
I am also learning by experimenting and leveraging the folks here who are smarter than me who are willing to help.
Iím just asking if there are more modern capacitor types that are better than silver micas for this purpose and if silver micas still retain these benefits at lower frequencies.


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« Reply #3 on: June 16, 2020, 10:12:18 am »
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ok , i undesrstand , here i've just downloaded this book i think it'll be ussefull for you request
The Capacitor Handbook by Cletus J. KAISER

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« Reply #4 on: June 16, 2020, 10:35:33 am »
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I found the book (2nd edition) on Amazon. I may pick one up.

Thanks.


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« Reply #5 on: June 17, 2020, 10:05:30 am »
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Quote:Posted by GarrettManRP
Are Silver Mica capacitors still a decent choice for capacitors in oscillator tank circuits due to their stability and low loss characteristics? Or have other types surpassed them now? And were they only for high frequency applications or do they function well at VLF frequencies too? Letís say VLF = 10 khz to 50 khz.

I am experimenting with a high efficiency tank circuit. I am building a spiderweb coil with Litz and Iím looking for a good cap to compliment it in a tank.





Litz wire is a Great idea.

Just letting you know , I am following your progress on your "Noiseless BFO/ IB" configuration.

Best regards and Please Stay Safe .

Eugene

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« Last Edit: June 17, 2020, 10:14:09 am by Eugene52 »
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« Reply #6 on: June 17, 2020, 12:39:51 pm »
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I also believe that litz wire is the best for coils, moreover I recovered litz wire from the disc of a 4500GPX and as the detective was a Chinese copy which went to the trash, I find myself with a good quantity of litz wire which could be useful to me in next metallic adventures, dear Eugene could you explain us the difference between the classic wire and the litz wire, thank you.

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« Reply #7 on: June 17, 2020, 01:35:59 pm »
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Quote:Posted by AK48
I also believe that litz wire is the best for coils, moreover I recovered litz wire from the disc of a 4500GPX and as the detective was a Chinese copy which went to the trash, I find myself with a good quantity of litz wire which could be useful to me in next metallic adventures, dear Eugene could you explain us the difference between the classic wire and the litz wire, thank you.



Hello AK48 and Everyone.

We discussed litz wire on this forum in 2014 . And it was more of an Argument than a Discussion. LOL
I think it has more advantages than disadvantages . It does have noise reduction in both Internal and external noise reduction.
And I read larger Magnetic fields are created using less current . More efficient.  Could be more efficient in VLF Type machines , less noise or external interference . Cleaner signal . Better sensitivity . I'm not an engineer but common sense tells me , use litz wire if you are having a noise problem.
On another note , I like DD search coils because they are easier to build and to final optimize or tune . A question is,  do all concentric search coils have a nulling coil ? So it will take extra time to get the concentric coil right. There is a way to final tune a DD search coil without an Oscilloscope. But DD is much easier . And also what I just learned is Rx does not have to be matched to Tx . I will talk about that later. The Forum Member GarrettmanRP is trying to build a Noiseless Colpitts BFO/IB  Metal Detector . He may have to use Litz wire on his search coil . And use his special capacitors in the search coil housing and again on his pcb circuit board. I'm not an engineer , but that's what I would do. Ltspice would be great to use [circuit simulation] I learn everyday . So nice to talk to people that are trying to make improvements or designing something new. I type as I go . So sorry if stuff is a little out of order and not edited. .  Please make comments, Thank-you.

Stay Safe !!!
Regards...........................Eugene



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« Reply #8 on: June 17, 2020, 02:53:06 pm »
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My understanding is that Litz wire per length has the least possible resistence due to the fact that it is made up of many strands of individually enamel coated wires. This basically gives you many parallel insulated wires and forces the current flow to traverse along each wire making use of more surface area within the bundle rather than traveling only on the surface of one big wire as described by the ďskin effectĒ behavior thus reducing the resistence. Iím no expert but I think this is typically important for high frequency signals and Iím not sure of the benefits at low frequency because Iím not sure where the powers that be draw the line between high and low. But my goal is to produce a highly efficient tuned LC tank with minimal losses from both components, the coil and the capacitor. But the plan is for the Litz to provide low resistence and the spiderweb coil design to provide low capacitance. If silver mica is the best choice of capacitor type then Iím hoping that will give me the lowest possible internal resistence and internal inductance and also temperature stability.
Time will tell. I wish I had more time to work on this but life keeps getting the way so itís slow going. ďWorking for a living is killing meĒ.



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« Reply #9 on: June 17, 2020, 03:42:23 pm »
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Quote:Posted by GarrettManRP
My understanding is that Litz wire per length has the least possible resistence due to the fact that it is made up of many strands of individually enamel coated wires. This basically gives you many parallel insulated wires and forces the current flow to traverse along each wire making use of more surface area within the bundle rather than traveling only on the surface of one big wire as described by the ďskin effectĒ behavior thus reducing the resistence. Iím no expert but I think this is typically important for high frequency signals and Iím not sure of the benefits at low frequency because Iím not sure where the powers that be draw the line between high and low. But my goal is to produce a highly efficient tuned LC tank with minimal losses from both components, the coil and the capacitor. But the plan is for the Litz to provide low resistence and the spiderweb coil design to provide low capacitance. If silver mica is the best choice of capacitor type then Iím hoping that will give me the lowest possible internal resistence and internal inductance and also temperature stability.
Time will tell. I wish I had more time to work on this but life keeps getting the way so itís slow going. ďWorking for a living is killing meĒ




GarrettManRP, Thank-You for all your posts on here !!!

And Please take your time. You have created some Good Topics worthy of discussion.

Everyone on the Forum are seeing Good New Topics now and having Positive Discussions .

Metal Detecting and Treasure Hunting is still a [Fantastic] #1 World Hobby  and you can social distance Too !!!

I am always Googling and researching stuff related to the discussions. It keeps me busy .

If I find anything Good when I Metal Detect , I will post a picture on the Forum here. Its been about a month since I dug some holes. Now the weather is going to be nice for a while, so I may be out Metal Detecting very soon.

Please Stay Safe !!!!

Eugene



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