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#1 2013-04-20 08:08:40

o0o0o0o
Contributor
From: Germany
Registered: 2011-10-06
Posts: 64

125 kHz antenna design and the AN710 equations for better range.

http://ww1.microchip.com/downloads/en/AppNotes/00710c.pdf

Using the documentation AN710 by Microchip, I trying to understand why... :

With a circular antenna of 13 cm (diameter) and 0.25 mm thick enamel wire.

50 turns :                                         
# LF antenna:  6.31 V @   125.00 kHz -/-
# LF antenna:  6.71 V @   134.00 kHz -/-
# LF optimal: 40.28 V @   193.55 kHz -/-

80 turns :                                                85 turns :
# LF antenna: 40.15 V @   125.00 kHz -/- # LF antenna: 22.42 V @   125.00 kHz
# LF antenna: 18.53 V @   134.00 kHz -/- # LF antenna: 10.34 V @   134.00 kHz
# LF optimal: 40.28 V @   126.32 kHz -/- # LF antenna: 40.15 V @   126.32 kHz

100 turns :                                              110 turns :
# LF antenna:  5.24 V @   125.00 kHz -/- # LF antenna:  3.76 V @   125.00 kHz
# LF antenna:  4.16 V @   134.00 kHz -/- # LF antenna:  3.22 V @   134.00 kHz
# LF optimal: 40.01 V @    96.77 kHz -/- # LF optimal: 40.01 V @    86.96 kHz

...why from 80 to 85 turns, there is a such a big difference of 17.43 V @ 125 kHz
and why an higher voltage gives a better read range (with 85 turns, 22.42 V, reading range is about 5 cm - with 80 turns, 40.15 V, reading range is about 6.5 cm).


To admin : please relocate my topic to http://www.proxmark.org/forum/viewforum.php?id=11 . Sorry about that.

Last edited by o0o0o0o (2013-04-20 11:07:55)

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#2 2013-04-20 08:17:03

o0o0o0o
Contributor
From: Germany
Registered: 2011-10-06
Posts: 64

Re: 125 kHz antenna design and the AN710 equations for better range.

Not being an electronics guy, I am not quite sure what is going on :

With the 80 turns :
When I am not touching the white cable of the hirose with my fingers, i get :
# LF antenna: 40.28 V @   125.00 kHz
# LF antenna: 20.14 V @   134.00 kHz
# LF optimal: 40.28 V @   123.71 kHz

If I touch the white cable (it doesn't do anything when I'm touching the red one) :
# LF antenna: 27.39 V @   125.00 kHz
# LF antenna: 11.55 V @   134.00 kHz
# LF optimal: 40.15 V @   117.65 kHz

And previous statement was wrong ! @ 27.39 V I get better reading range than @ 40.28 V...

Is my body acting as a capacitor or something ?

For Equation 1 of the documentation, what is the Current I through the antenna ?

Last edited by o0o0o0o (2013-04-20 08:53:42)

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