19/09/18
Page 47 of 67
ASR650 Operational Manual
In the next example curve we put the antenna closer to metal. Metal decreases the antenna
inductance and thus the reader has to set more Autotuning capacitors for compensating the
reduced inductance.
Due to the presence of metal the reader has decided for a Capacitor Pattern of 15. In this case,
the yellow LED will be activated slightly longer. What one can also see is that the amplitude has
decreased from 87.1V to 84.2V which leads to the following, very important, conclusion:
Although the Autotuning can compensate a lower antenna inductance, it can
never compensate the losses caused by too much metal. Even if the reader
is still able to tune for the correct resonant frequency, there will be a reduced
reading performance. So, you should always try to modify your application in
a way that there are no losses like this.
In case the ASR650 is used at maximum transmit power, the minimum required antenna
impedance is 750
Ω. In the screenshot on the left side, it is only slightly above this limit. In the
example on the right side, it is just below the limit and the error code ‘
Low Ant. Q
’ will be shown.
This is due to the low antenna impedance. You either have to separate the antenna further from
metal or set a lower transmitter voltage. Both measurements were done in the same situation and
it becomes obvious that values can vary, so make sure your antenna impedance is always well
above the required minimum.
