Problem to use RF front-end for 13.56 MHz application

Question

Hi,
I developed an ASK transceiver using 5640R. It worked well when I directly connected the AI and AO ports. Then I tried communications between two antennas. I cascaded the niTuner VI and RF Upconverter Only Mode VI to control the PXI-5600 and PXI-5610 as separate modules. I connected the two antennas to 5600 RF downconverter input and 5610 RF upconverter output respectively. But when I ran it, all I received was noise. I checked the upconverter Only Mode Vi, and I found out that the 13.56 MHz RF frequency might be a problem. The error would occur that the IF carrier frequency is an invalid value. And the smallest value for IF should be 14 MHz. So it seems that for 13.56 MHz, I cannot set an IF to satisfy the minimum IF value requirement.
I think I should be able to use this box for 13.56 MHz applications. So does anyone know the solution for this problem?
Thanks for help!
Danlu

Answer 1

Hi Danlu,
The PXI-5610 can only tune in 1 and 5 MHz step sizes based on bandwidth. For BWs larger than 10 MHz, the 5610 will tune in 1 MHz steps, and for BWs smaller than 10 MHz the 5610 will tune in 5 MHz steps. Thus, a center frequency of 13.56 MHz will not be immediately possible with th 5610 since it is not divisible by 1 or 5 MHz.
To compensate for this, I would suggest that you tune to 15 MHz (if you are selecting a narrow) or 13 MHz (if you are selecting a wide bandwidth). For the remaining frequeny offset, you can adjust the NCO of the 5640R.
For example » tune the 5610 to 15 MHz, and tune the NCO 25 MHz - 1.54 MHz = 23.56 MHz. This will place you at the correct center frequency when combining the two devices. This is how we perform fine tuning with respect tof frequency for our PXI-5661 and PXI-567x products.
Regards,
Chris Behnke
Sr. RF Engineer
High Frequency Measurements