Hi, I am using the M7E hector connected via USB on rasperry pi. My external antenna worked initially but now everytime i run it it contantly reports a high return loss. Does anyone have a way to fix this or an idea of what the issue is. My resistor is in the correct spot, and I am wondering if one of the wires got damaged.
There was an earlier issue (M7E High Return Loss - Sensors / NFC & RFID - SparkFun Community). Can you check the recommendations.
Other thoughts :
What power setting do you use ?
Do you use an external strong power-supply?
Pictures of the changed 0 ohm resistor ?
I was originally testing at 27 dBm, which is the max power setting, but I also tried lowering it to 20 dBm and the reader still kept printing:
RFID High return loss, check antenna!
For power, I am currently powering the setup through the Raspberry Pi/USB setup, not a separate strong external power supply for the RFID reader. The Pi is using USB-C power, but I do not currently have a dedicated external supply going directly to the RFID module.
I do not have a photo of 0 ohm resistor right now, and the thing I canât wrap my head around is I initially tested my RFID with the external antenna in my room with 20 dBm and it worked. Then I deployed my system to my large school project which is using it on garage to track when cars enter. It worked for first test, but then when I powered off rasperry- pi, everytime i ran the system the high return loss happened.
Personally I have been wondering about root causes this can have. Sorry for the longer reply..
The high return loss can have multiple reasons as stated in the earlier response. Under normal conditions a return loss is good. It means that most of the signal that was send has been transmitted and a strong enough return = reflection from the TAG has been received.
But an error âhigh return lossâ means that it is TOO HIGH. The sending RFID signal does not look like to be used. The (reflected) power on the line is much higher than expected. It is in 80% of the cases related to bad connections, wiring and / or antenna mismatch. A good article is https://medium.com/@dtr336108/what-is-return-loss-why-is-it-important-68fd9e1f3de9.
Hence the first step is to check connectors, cabling etc. But it is also the question about the 0 Ohm resistor. If that connection is not good enough, no or not enough signal is passed to the antenna.
Talking about the antenna, for the M7E it needs 50 ohm impedance to make a perfect match. Looking at the M6E, https://www.jadaktech.com/wp-content/uploads/2022/12/ThingMagic-M6e-User-Guide-Rev-01242019-1.pdf, nearly the same as M7E It expected a certain combination:
If you antenna has a TOO high gain, it can impact the power your reflecting reading. The M7E might assume the reflected signal is to strong
Then the environmental impact. Maybe there are other RFID signals/sources in the same area. Actually I would not be surprised about that as there are many systems that make use of the free UHF bands for your area. Like contact access RFID cards, garage door openers etc. They can increase the UHF signal received / read by the antenna / M7E. But a Iron roof could also be reflecting more than expected
Last⌠but not least. The M7E, like the M6E, is very sensitive to the strong power supply that can handle bursts. Not sure a Raspberry Pi has the capacitors to handle the burst request for reading. A wall wart will not do the job.
So try this :
Double check cables, zero ohm resistor etc.
Check Antenna specs
Try to reposition the antenna, maybe pick up less external RFID.
Try running the example readerstarts.c, and set TMR_ENABLE_UHF as part of your compile ( -d TMR_ENABLE_UHF). See what it tells you on the different antenna setting
Apply strong external power supply
Reduce the reading power, see what happens.
Thank you so much for all this information, I will try this all today. I hope itâs the cables and not something else like needing external power supply
Perhaps, the center pad (directly under ârfâ label) does look like a âcoldâ solder joint/appears to be floating atop the solder a bitâŚmaybe grab some flux/wick and re-try?
Agree with TS-Russell. Instead of a zero ohm resistor, you can also solder a small wire between the 2 points. Sometimes easier to solder.
Just one more question, given that you use high power, do you provide a cooling block to the M7E? It will get hot soon and stops at about 72 C.
I do not currently have a cooling block. Where/which/how do I get one?