problem to use RF front-end for 13.56 MHz application

[CC14]

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

[Speedy_Badger]

Hello Danlu,

The PXI-5610 has a 25 MHz IF center frequency with a 20 MHz bandwidth around it. 13.56 MHz is unfortunately just shy of the lower end of this range. Is there a reason why you cannot generate at a higher IF?

The PXI-5600 will be fine on the other hand, it has a 15 MHz IF center frequency with the same 20 MHz bandwidth centered around it.

Regards,

[CC14]

Thank you very much for the quick reply!

 The problem is for my system, the operating frequency is 13.56 MHz, so I need to choose an IF lower than that. 

So can I use this front-end for my application? Do I choose the wrong vi?

Thank you again!

Danlu

[Speedy_Badger]

Hi Danlu,

I think we are confusing a couple ideas - Your IF frequency is independent of your end RF frequency. If you set your IF frequency to 25 MHz and your RF frequency (via the PXI-5610 and the RFSG driver) to 13.56 MHz, you our output frequency will be 13.56 MHz.

Keep in mind, the PXI-5610 requires an IF frequency of 25 MHz with a maximum bandwidth of +/- 10 MHz. The RF output of the PXI-5610 ranges from 250 kHz to 2.7 GHz however so you can still achieve your final frequency. That being said, if your operating frequency is 13.56 MHz, why do you need to implement the PXI-5610?

Regards,

[CC14]

Hi,

Do you mean that for my case, I can hook the FPGA directly to the antennas? I've tried this way, but if the signal is not large enough, I may encounter significant noise. So I try to implement the 5610. And in this way, I can set the parameters like gain, bandwidth, etc..

I also tried to set the RF frequency to 13.56 MHz, and Upconverter IF frequency to 25 MHz using the RFSG Upconverter Only Mode vi. Is this the correct way? However, it doesn't work. I'm wondering if the "Actual Upconverter Center Frequency" is the RF output frequency? Why is it 15 MHz if I set the values as above? Will it matter?

Thank you very much again!

Best,

Danlu

[Speedy_Badger]

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,