# MFRC522 With External Antenna Not Working **URL:** \ **Category:** General Guidance\ **Created:** [May 16, 2021, 11:02pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615 "2021-05-16T23:02:00Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![imthecarlos](https://avatars.discourse-cdn.com/v4/letter/i/df788c/32.png) [@imthecarlos](https://forum.arduino.cc/u/imthecarlos)\ **Post date:** [May 16, 2021, 11:02pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/1 "2021-05-16T23:02:00Z")
Hello! I'm trying to create a custom UHF RFID reader with the goal of extending its range. I modified the MFCR522 chip in order to destroy the old antenna and connect a separate 5dBi UHF RFID Antenna capable of 902-928M with an SMA connector. Which J# should I connect the leads from the old antenna to? Currently it's connected to J6 but it does not work. I uploaded the MFCR522 RFID Arduino Library by miguelbalboa and ran the "DumpInfo" example sketch but it cannot detect any cards. What am I doing wrong? I have my hardware setup attached below. ![16212060244818893355519103651377](https://europe1.discourse-cdn.com/arduino/original/4X/a/8/a/a8a6212044bec102140e323923c67b59c0cf5eea.jpeg) ---
**Author:** ![Paul\_KD7HB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paul_kd7hb/32/1127958_2.png) [@Paul\_KD7HB](https://forum.arduino.cc/u/Paul_KD7HB)\ **Post date:** [May 17, 2021, 12:58am UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/2 "2021-05-17T00:58:27Z")
Does your backup board still work? Paul ---
**Author:** ![imthecarlos](https://avatars.discourse-cdn.com/v4/letter/i/df788c/32.png) [@imthecarlos](https://forum.arduino.cc/u/imthecarlos)\ **Post date:** [May 17, 2021, 1:24am UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/3 "2021-05-17T01:24:19Z")
Yes, it should. Unless you're referring to the internal antenna of the RC522 that I dremmeled off, in which case no. I do however have a spare RC522 chip. ---
**Author:** ![Paul\_KD7HB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paul_kd7hb/32/1127958_2.png) [@Paul\_KD7HB](https://forum.arduino.cc/u/Paul_KD7HB)\ **Post date:** [May 17, 2021, 2:49pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/4 "2021-05-17T14:49:04Z")
Yes, the antenna. Next time, just cut the trace going to the antenna, so you can solder bridge over the cut to restore the original antenna. Paul ---
**Author:** ![JohnLincoln](https://avatars.discourse-cdn.com/v4/letter/j/7ba0ec/32.png) [@JohnLincoln](https://forum.arduino.cc/u/JohnLincoln)\ **Post date:** [May 17, 2021, 7:20pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/5 "2021-05-17T19:20:13Z")
As far as I know the MFRC522 operates at 13.56MHz. [MFRC522 datasheet](https://www.nxp.com/docs/en/data-sheet/MFRC522.pdf) ![](https://europe1.discourse-cdn.com/arduino/original/4X/a/c/b/acb977b6382783954b9fa73416339f0fe3df7439.jpeg) That bank of capacitors C6,C7,C8,C9,C10, C11 is used to form a resonant circuit with the 4 turn coil that you have irreversibly removed. It _was_ tuned to the operating frequency. I think that the antenna that you have fitted is totally wrong for the frequency of operation. ---
**Author:** ![Paul\_KD7HB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paul_kd7hb/32/1127958_2.png) [@Paul\_KD7HB](https://forum.arduino.cc/u/Paul_KD7HB)\ **Post date:** [May 17, 2021, 7:36pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/6 "2021-05-17T19:36:02Z")
Good catch! And at that frequency, the RFID is sensed by direct induction. Paul ---
**Author:** ![imthecarlos](https://avatars.discourse-cdn.com/v4/letter/i/df788c/32.png) [@imthecarlos](https://forum.arduino.cc/u/imthecarlos)\ **Post date:** [May 17, 2021, 10:24pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/7 "2021-05-17T22:24:47Z")
How would one calculate the capacitance needed for this type of antenna? Also, I looked at some other designs and came up with a theory I hope you could confirm or deny. Would the antenna hook up to a separate UHF reader via the SMA port (that I have yet to obtain), and the J1-6 ports are for supplying added power to boost the antenna. Is this correct, or do I have it backwards and it's more like I have it currently? ---
**Author:** ![Paul\_KD7HB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paul_kd7hb/32/1127958_2.png) [@Paul\_KD7HB](https://forum.arduino.cc/u/Paul_KD7HB)\ **Post date:** [May 17, 2021, 10:41pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/8 "2021-05-17T22:41:54Z")
Forget the antenna idea. It is a tuned coil, tuned to the 13.56MHz frequency. Two adjacent coils tuned to the same frequency will share the same power. IT is a transformer, not a transmitter and receiver. Paul ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [September 14, 2021, 10:41pm UTC](https://forum.arduino.cc/t/mfrc522-with-external-antenna-not-working/862615/9 "2021-09-14T22:41:57Z")
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