Why Does Our Power Mapper Get Inconsistent Readings?


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Ask The ExpertsCategory: QuestionsWhy Does Our Power Mapper Get Inconsistent Readings?
MK Dani asked 11 months ago
I have an ePix Power Mapper. Can you please explain the following phenomenon? When the Power Mapper is placed next to an RFID tag to check how much power the tag is receiving, the Power Mapper shows the power reading and the tag is also read, but many times the Power Mapper shows the same power reading yet the tag is not read. Why does this happen and how can we correct it?


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To answer your question, I reached out to Dave Mapleston, the founder of ePix, which makes the Power Mapper. Here’s his response:

“At these frequencies, a quarter wavelength is just 81 millimeters. This means that you could have a full signal on the meter and then, just 81 centimeters away, no signal at all. Readers cope with this by using I and Q receivers; one receiver is in phase and the other is 90 degrees out of phase. Unfortunately, precision is needed to get meaningful results. Also, having the tag and the meter in close proximity will cause shadowing. They will feed off each other, causing low readings and sometimes no readings, then remarkably twice the reading.

“The answer is to remove the tag and, with the meter attached to a non-conductive pole, move the meter around within around 10 centimeters of the tag’s location. This will give a good average of the signal. The highest signal is the most accurate reading, due to the I and Q reader trick. What we also look for is changes when the meter is moved up and down. Rapidly changing levels at different heights indicate a lot of constructive and destructive signals bouncing off the ground.”

I hope you find Dave’s answer helpful.

Mark Roberti
Founder and Editor
RFID Journal


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