# M7E High Return Loss **URL:** \ **Category:** NFC & RFID\ **Created:** [May 30, 2024, 1:43pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498 "2024-05-30T13:43:20Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![PSchultheis](https://avatars.discourse-cdn.com/v4/letter/p/34f0e0/32.png) [@PSchultheis](https://community.sparkfun.com/u/PSchultheis)\ **Post date:** [May 30, 2024, 1:43pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/1 "2024-05-30T13:43:20Z")
I am attempting to use the M7E RFID reader, with the antenna and cables recommended onsite, using URA 6.2 [https://www.sparkfun.com/products/14131](https://www.sparkfun.com/products/14131) [https://www.sparkfun.com/products/14132](https://www.sparkfun.com/products/14132) [https://www.sparkfun.com/products/662](https://www.sparkfun.com/products/662) I am powering via USB, and have switched the 0ohm resistor to external antenna setting. Antenna selected is one, baud rate is 115200 I assumed NA is North America for region, but also tried OPEN. GEN2 protocol is selected, and the tags I’m using are GEN2 as well When I attempt to read the RFID tag, I get “The module has detected high return loss and has ended RF operations to avoid module damage” This occurs at dBm settings from 27 all the way down to 0 It occurs with different tags of different manufacture. It occurs if I read but do not have a tag present at all What am I doing wrong? ---
**Author:** ![paulvha](https://avatars.discourse-cdn.com/v4/letter/p/65b543/32.png) [@paulvha](https://community.sparkfun.com/u/paulvha)\ **Post date:** [May 30, 2024, 2:13pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/2 "2024-05-30T14:13:17Z")
According to the URA source code this: Excess power detected at transmitter port, usually due to antenna tuning mismatch. According to the Thingmagic user guide : error 0x505 The module has detected a poor return loss and has ended RF operation to avoid module damage. Take steps to resolve high return loss on receiver: - Make sure antenna VSWR is within module specifications - Make sure antennas are correctly attached before transmitting - Check environment to ensure no occurrences of high signal reflection back at antennas. Seems related to the antenna connections. ---
**Author:** ![PSchultheis](https://avatars.discourse-cdn.com/v4/letter/p/34f0e0/32.png) [@PSchultheis](https://community.sparkfun.com/u/PSchultheis)\ **Post date:** [June 4, 2024, 3:09pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/3 "2024-06-04T15:09:35Z")
Antenna is correct, connections are solid, tried using alternate connectors just in case. Put attenuators in line, anywhere from 2dB to 20dB, no success. ---
**Author:** ![paulvha](https://avatars.discourse-cdn.com/v4/letter/p/65b543/32.png) [@paulvha](https://community.sparkfun.com/u/paulvha)\ **Post date:** [June 4, 2024, 3:25pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/4 "2024-06-04T15:25:38Z")
what happens if you remove the external antenna and switch back to use the on-board antenna? ---
**Author:** ![PSchultheis](https://avatars.discourse-cdn.com/v4/letter/p/34f0e0/32.png) [@PSchultheis](https://community.sparkfun.com/u/PSchultheis)\ **Post date:** [June 5, 2024, 5:25pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/5 "2024-06-05T17:25:51Z")
Same thing. I’m suspecting something very simple that I’ve overlooked, but can’t seem to find what. ---
**Author:** ![paulvha](https://avatars.discourse-cdn.com/v4/letter/p/65b543/32.png) [@paulvha](https://community.sparkfun.com/u/paulvha)\ **Post date:** [June 5, 2024, 6:49pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/6 "2024-06-05T18:49:19Z")
weird… very weird… I wonder whether this is due to the latest 6.2 version of the URA. Somewhere I read before the latest mercuryAPI (and thus URA) should only be used from a certain firmware level on the boards… maybe an earlier URA will work. I will try tomorrow on my M6E. Else the components on your boards could have an issue… ---
**Author:** ![paulvha](https://avatars.discourse-cdn.com/v4/letter/p/65b543/32.png) [@paulvha](https://community.sparkfun.com/u/paulvha)\ **Post date:** [June 6, 2024, 9:14am UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/7 "2024-06-06T09:14:35Z")
I tested my M6e and URA 6.2 and it worked without problems. Stayed on 5db read power to keep a stable USB, EU3, 115K speed, used a USB/serial which is set to 5V VCC ( **check that on yours as many are by default 3v3 VCC** ), onboard antenna. Maybe check you have the firmware on the M7E V2.1.3 or higher (URA, connect to the M7E, select Status/version info) Else it looks like a problem with your board, maybe a short circuit on the antenna. About loss return & VSWR found an attached document to explain that a bit more [ThingMagic\_M7E\_Power\_App\_Note.pdf](https://community.sparkfun.com/uploads/short-url/rLSiqwLiJijWrDL0r8LB85mSfLj.pdf) (340 KB) ---
**Author:** ![PSchultheis](https://avatars.discourse-cdn.com/v4/letter/p/34f0e0/32.png) [@PSchultheis](https://community.sparkfun.com/u/PSchultheis)\ **Post date:** [June 12, 2024, 2:42pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/8 "2024-06-12T14:42:23Z")
Cut the trace to set 5V, no change. ---
**Author:** ![paulvha](https://avatars.discourse-cdn.com/v4/letter/p/65b543/32.png) [@paulvha](https://community.sparkfun.com/u/paulvha)\ **Post date:** [June 12, 2024, 2:58pm UTC](https://community.sparkfun.com/t/m7e-high-return-loss/47498/9 "2024-06-12T14:58:06Z")
I assume you could read the firmware level and if so I can only conclude a problem with your board with the antenna circuit/traces. I would ask for a replacement Maybe share some pictures about the antenna select and if I do a cold ohm measurement, no power is applied, between GND and the antenna select I get 0.3 ohm. Maybe check that. else I would ask for a replacement