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RFID antenna

So I have this OMNIKEY 5534 MultiTag Reader, and according to the manual a test-antenna can be made with a coil of 70 turns with a 0.22mm magnet wire around 36mm spool.
That works great, but I need the spool to be 80mm in diameter, -so the question is, how many turns should I use with a MW30 (0.25mm) wire?

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i believe the math goes like this:

36mm x 3.14 = 113.04mm
x70 = 7912.8mm (full length of wire)
/ 3.14= 2520
/80=31.5

=31.5 turns

does that make sense?

No promises that it is even correct.

This calculator, http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=18878, and this pdf, http://ww1.microchip.com/downloads/en/appnotes/00678b.pdf, gave me the answer I will give you.

According to the calculator, the antenna you are told to make, in single layer form, must be as long as it is around. So, you will have about 123uH. To meet the same inductance you will need 47 turns on an 8cm long by 8 cm diameter cylinder. Making a single layer coil requires the extra length to allow for more discretion in the frequency recognition(info from page 8 and 4 of the pdf).

Thank you for this information Bridmun.
This is the build instructions for the test-antenna.

Test-Antenna 

  • Tightly wind 70 turns of 0,22mm enameled solid copper wire on 36mm diameter. 
  • Leave about 50 mm free at one end and about 30mm at the other, cross the wires (at the +/- 30 mm point) and secure them together using the tape 
  •  Twist a 4mm diameter Spri-band onto the coil that you have just made, leaving the start and finish ends free. 
  •  Solder an 11Ohm resistor (½W, R ±1%) in series to the shorter end of the free antenna leads.
     This should lead to an antenna with 395 μH and a Q=20,5.

I did not wind mine as a single layer, but wires overlapping to a spool of about 3-4mm in diameter (cross section). But it works fine.

It also states that the antenna should have an inductance between 356 and 435 uH