How i increase frequency of my coil?

[chuubaba]

I am building coil for my TGSL board. I wind the enamelled copper wire 101 turn and measure the frequency on my analog o-scope set at 10uS and 5V. It is showing 7.25 divisions that interprets as 13.79KHz. Do i need to add more turns to the coil or should i remove some number of turns? I am looking to achieve 14.5KHz resonance frequency for Tx and 16.1KHz for Rx.

[kt315]

Chu

you do much noise. i think you want torpedo this forum. certainly 'show must go on' but not in this degree.

[chuubaba]

you have a serious constipation problem. Instead of being a self proclaimed corrupt policeman you must go and see a physician and a psychologist You could easily write a solution to my problem instead of you ugly words.

[dbanner]

*******.

[Skippy]

Maybe we can ask George/Carl to change KT's title from "Guru" to "Constipated Forum Policeman" , he-he!

Back on topic:
Mr. Chu - you need to REDUCE your turns, in order to REDUCE inductance, and INCREASE resonant frequency.

* Inductance of a coil varies almost exactly with the SQUARE of the number of turns, eg. change 100T to 120T gives inductance increase
(1.2 x 1.2) = 1.44 times the starting value.

* Resonant freq is F, and
2*pi*F = [sqrt( L*C )]^-1
So for example if you halve inductance, freq increases by [0.707]^-1 = 1.414 times

Knowing this, you should be able to work out that you need 96 turns on your coil to give the correct higher freq.

I hope this beginners example helps other coil builders out there, not just Chu.

[dbanner]

There is another way of doing this. Assuming you have already wrapped your coil and shielded it, then go from the other way around. That is to work out the cap values for the collpits oscillator to achieve 14.5khz. C1*C2/C1+ C2 gives the effective capacitance for the resonance calculator. So instead of changing inductance of coil, change the resonating capacitance of oscillator. Reduce slightly one of the capacitor in the collpits oscillator and resonant frequency of the TX will increase. See?

[chuubaba]

There is another way of doing this. ....

Very interesting. Kt315 once said we could use a variable capacitor like component. Did you ever see any practical form of this idea?
The formula you give for working out capacitor value will be easy to understand if illustrated using my coil data above

[dbanner]

Chu, you would make a great comedy script writer in Hollywood. Pack your bags and take the first flight available.

[Andi68]

[chuubaba]

These coils are difficult to make and this is just the start. I began with a very shallow coil. Looking to solve it i reduced turns but no improvement and then i found this post and went on to implement it but lost the minimum depth i already had. Now i have reverted the changes but it beeps with on and off only. I think my problem is in failing to read the o-scope. Failing to read where a wave cycle begins and ends. Here is a picture of the 6.9 divisions i read from my coil . The scope was put to 10 uS and 5 V. I hope i read it correct.

[rickb]

chuubaba:

Do you not know the relationship between time and frequency, and how to solve for one when you have the other? The scope show a time period of about 69 uS. The freq is therefore about 14.5 KHz. Pretty damn close if you ask me. Now, how did I arrive at that figure?

It sounds like your problem might be adjusting the balance between coils for minimum output.

[chuubaba]

chuubaba:

Do you not know the relationship between time and frequency, and how to solve for one when you have the other? The scope show a time period of about 69 uS. The freq is therefore about 14.5 KHz. Pretty damn close if you ask me. Now, how did I arrive at that figure?

It sounds like your problem might be adjusting the balance between coils for minimum output.

I have nulled it with DMM to -0.10V on pin 5 of U103 and with o-scope to minimum of ???? on pin 7 of U101. It has indeed shown much better sensitivity but the tone from far metal objects is faint and pulsatile while only those within 2 or 3 cm range produce tone. Also the iron seems to be always rejected and all pots apparently don't seem to work.

[rickb]

Measure the 14.5 Khz signal at pin 7 of U101A. (coil pre-amp)

download and study the tgsl pdf 101 parts 1 and 2. in the below link.

http://www.geotech1.com/forums/showt...5456#post95456

read and understand this post

http://www.geotech1.com/forums/showt...6683#post86683