Trying to build LF antenna for the first time

buymeanapple · 2014-02-18 01:19:26

Hello,

This is my first time working with antennas and frequencies and I seem to be drinking through a fire hose. I have looked at the antenna guide on the wiki but it seems to only have a guide for a HF antenna. Is there a place that I can go that would help point me in the direction of how to build a LF antenna?

Like I said this is my first time working with this kind of stuff. I am working on RFID research for my capstone (CIS major) and, at the moment, I am just trying to figure out how to read tags.

I also am using the PM3.

aleza84 · 2014-03-12 20:15:20

Start checking these:

http://ww1.microchip.com/downloads/en/devicedoc/51115f.pdf
http://www.priority1design.com.au/rfid_coil_antenna.html

Antenna inductance is very important: 500uF-1000uF
Gauge of the wire you are using also is important.... after that... depending on those two values... with an online calculator or this page.... du the number of turns. (check http://todbot.com/blog/2007/08/09/adding-a-remote-antenna-to-parallaxs-rfid-reader/)

Also, http://www.proxmark.org/files/J.Westhues/proxmark3-eagle.zip havent tried to make this PCB 125khz antenna done there.

Post your findings.

buymeanapple · 2014-03-20 06:42:43

Thanks for the response it really helped point me in the right direction. I will post my findings once I complete the antenna.

buymeanapple · 2014-03-24 08:40:59

I have done what was recommended and still have not succeeded in reading tags successfully.

Here is my tune command:

and here is a picture of my antenna:

I can't seem to figure it out...

vivat · 2014-03-24 09:55:18

I see that your antenna resonates at 375 khz
Add few turns and make sure LF Optimal is nearly 125 khz.

Enio · 2014-03-24 09:56:34

Lf read
Data samples 40000
Data plot

will show you the wave for 125khz tags. Antenna should resonate close ti desired read frequency.

demodulating it - depends on the kind of tag.

Last edited by Enio (2014-03-24 09:57:39)

buymeanapple · 2014-03-31 21:38:03

After trying a few things suggested I just ended up buying the pre-made one from Proxmark. Turns out making an LF antenna is extremely difficult when I know very little about antenna design.

Thank you guys though for all of your help. Now I just need to figure out how to make a HF antenna....

iceman · 2014-04-26 12:02:53

I just tried myself to make an LF-antenna.

[block]
proxmark3> hw tune
#db# Measuring antenna characteristics, please wait...
#db# Measuring complete, sending report back to host

# LF antenna: 22.29 V @ 125.00 kHz
# LF antenna: 16.38 V @ 134.00 kHz
# LF optimal: 22.29 V @ 125.00 kHz
# HF antenna: 0.77 V @ 13.56 MHz
# Your HF antenna is unusable.
proxmark3> hw tune
#db# Measuring antenna characteristics, please wait...
#db# Measuring complete, sending report back to host

# LF antenna: 20.95 V @ 125.00 kHz
# LF antenna: 16.38 V @ 134.00 kHz
# LF optimal: 20.95 V @ 125.00 kHz
# HF antenna: 0.77 V @ 13.56 MHz
# Your HF antenna is unusable.
proxmark3>
[/block]

I used:
- 0.1mm cupper, emal
- 7cm diameter

measure ohm: 51

First tune is without a lf-tag, and second is with tag present.

Even if the the antenna seems to resonate at 125khz, optimal, it doesnt seem to be able to read the tag.

Enio · 2014-04-26 12:30:32

iceman wrote:

Even if the the antenna seems to resonate at 125khz, optimal, it doesnt seem to be able to read the tag.

Can you post a picture of the captured wave? I ha similar issues once, getting a really bad wave despite almost perfect voltage. When i removed a few turns effectively making my antenna worse on voltage, it worked. Im not sure about the exact reason.

iceman · 2014-04-26 18:05:12

It is just noice...

data samples 16000

http://www.icesql.se/proxmark3/wave.png

iceman · 2014-04-26 18:13:18

The measurements given was wrong of me. The diameter is 12.5cm, the radius is 6.25cm

Enio · 2014-04-26 19:06:36

I had the exact same. Have you ttied removing some turns?

iceman · 2014-04-26 19:15:57

I started with 90+ turns,
which I had to strip off about 15 to get to this, and now I took one more turn... still just noice...

I will keep on removing loops.. one by one...

iceman · 2014-04-26 20:18:16

I so dislike the hirose contact now...

iceman · 2014-04-28 22:01:09

After reading a tip about LF, in a different thread, I managed to get my LF antenna to give me something better then noise.

http://www.icesql.se/proxmark3/wave2.png

proxmark3> hw tune
#db# Measuring antenna characteristics, please wait...
#db# Measuring complete, sending report back to host

# LF antenna: 20.41 V @   125.00 kHz
# LF antenna: 16.25 V @   134.00 kHz
# LF optimal: 20.54 V @   126.32 kHz
# HF antenna:  0.74 V @    13.56 MHz
# Your HF antenna is unusable.
proxmark3>

The tip was to use::

1) lf read
2) data samples 16000
3) data plot

Is it something with powering up the LF path?

vivat · 2014-04-29 03:53:58

May be it is not 125 khz tag? Or it is damaged?

iceman · 2014-04-29 06:21:11

No, the tag is correct and working. I've a wafer lf-antenna from xfpga since earlier that works.

However, I've been looking into the code behind the commands "lf read" and "data samples nnnnn"

vivat · 2014-04-29 08:07:34

Maybe your tag is small? You need a smaller antenna in that case.

iceman · 2014-04-29 17:38:05

could be that the antenna is too large but it is the size of a cd-case so I doubt it.

Think it could be the connections between cupperthread and cable.

back to testing..

asper · 2014-04-29 18:45:53

Cd size? It is big!

asper · 2014-04-29 18:51:47

Cd size? It is big!

Proxmark3 community

Announcement

#1 2014-02-18 01:19:26

Trying to build LF antenna for the first time

#2 2014-03-12 20:15:20

Re: Trying to build LF antenna for the first time

#3 2014-03-20 06:42:43

Re: Trying to build LF antenna for the first time

#4 2014-03-24 08:40:59

Re: Trying to build LF antenna for the first time

#5 2014-03-24 09:55:18

Re: Trying to build LF antenna for the first time

#6 2014-03-24 09:56:34

Re: Trying to build LF antenna for the first time

#7 2014-03-31 21:38:03

Re: Trying to build LF antenna for the first time

#8 2014-04-26 12:02:53

Re: Trying to build LF antenna for the first time

#9 2014-04-26 12:30:32

Re: Trying to build LF antenna for the first time

#10 2014-04-26 18:05:12

Re: Trying to build LF antenna for the first time

#11 2014-04-26 18:13:18

Re: Trying to build LF antenna for the first time

#12 2014-04-26 19:06:36

Re: Trying to build LF antenna for the first time

#13 2014-04-26 19:15:57

Re: Trying to build LF antenna for the first time

#14 2014-04-26 20:18:16

Re: Trying to build LF antenna for the first time

#15 2014-04-28 22:01:09

Re: Trying to build LF antenna for the first time

#16 2014-04-29 03:53:58

Re: Trying to build LF antenna for the first time

#17 2014-04-29 06:21:11

Re: Trying to build LF antenna for the first time

#18 2014-04-29 08:07:34

Re: Trying to build LF antenna for the first time

#19 2014-04-29 17:38:05

Re: Trying to build LF antenna for the first time

#20 2014-04-29 18:45:53

Re: Trying to build LF antenna for the first time

#21 2014-04-29 18:51:47

Re: Trying to build LF antenna for the first time

Board footer