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#1 2009-01-29 14:37:15

henrym97
Contributor
From: North America
Registered: 2009-01-23
Posts: 18

50 ohm antenna match?

Has anyone out there experimented with matching the PM3 antenna interface to 50 ohms so it could be used with available HF antennas?

I have several parallel LC antennas matched to 50 ohms from other systems that I was hoping to try.  I know how to 2-element match the input but wanted to see if anyone else has already been down this road.


~Henry

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#2 2009-02-10 17:48:40

edo512
Contributor
Registered: 2008-10-07
Posts: 103

Re: 50 ohm antenna match?

Hi Henry,

  Have you actually tried to use the antennas on a Proxmark3? What were your results? I should be receiving a few antennas shortly, I'll also try on my side,

Ed

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#3 2009-02-12 23:05:20

henrym97
Contributor
From: North America
Registered: 2009-01-23
Posts: 18

Re: 50 ohm antenna match?

Hi Ed! 

Glad to see someone else is still working with the antennas!  I've had decent results with my 50 ohm antennas without much additional matching, only tuning of parallel RLC circuits.  One that seems to work particularly well and is small was a RR-IDISC-ANT4-3-A from Digi-key (though kind of pricey).  It gave read ranges of about 3 cm. 

I also made up some antennas using copper tape and a few trimmer caps.  This seemed to work almost as well and was a lot cheaper.  With larger loops I could get 3 - 4 cm.   I made a fixture for the PM3 that attaches an SMA connector to the test points.  That way I could attach my homemade antennas (which also have SMA connectors) via coax.  This avoids the TL effects and allows the antenna to be located pretty far away from the device.

Either way you'll probably have to tune the antennas slightly (or tune the PM3 by changing C35/C36), but you should get it to work.  The RR antenna has a trimmer cap so that is nice.

I'm currently having some PCB antennas fab'd I designed using EAGLE PCB.  I'll let you know the results of those when they come in (hopefully next week).

Good Luck!

Henry


~Henry

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#4 2009-02-21 20:21:05

edo512
Contributor
Registered: 2008-10-07
Posts: 103

Re: 50 ohm antenna match?

I made a try with Gemalto Prox C2 Antenna Device (store.gemalto.com, 23€), which is a 50Ohm antenna equipped with a tuning cap, but was not able to get good results: no matter what I try I cannot get over 2V with the 'tune' command. I use the coax that is shipped with the antenna & connect it using a hirose connector.

  Next i'll try to use the antenna of a contactless smartcard inlay: has anyone else tried to go down this path? What sort of cable would be recommended in order to make this work properly?

ed

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#5 2009-02-23 13:19:09

henrym97
Contributor
From: North America
Registered: 2009-01-23
Posts: 18

Re: 50 ohm antenna match?

Ed,

Could be the tuning cap on your antenna doesn't have enough range to tune to resonance.  You might try putting another tuning cap in series with your antenna, adjusting the series and parallel cap (on the antenna) together should be able to get you a better match.  The PM3 was designed to just connecto to a coil, so you are going to have some loss in the impedance match.  Keep trying the 'tune' command until you've maximized the voltage.   

I've never tried a card inlay loop, but I know the inductance will probably be higher so for resonance, the 50 pF cap on the PM3 might have to be adjusted to get it to work.  It might be easier to wind some wire around a form to get the required inductance and then you can change the shape to maximize your voltage.  There are some great app notes and discussion about how to do this in the other threads.


~Henry

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