Schematic?

[EricTheRed]

My name is Eric Beutlich and I am a student researcher at Texas Tech University.

I have been trying to set up the FM Demo to listen to local radio stations through the ni5640 board. All that comes out is strange noise. I am a little uncertain about the internal setup of the board, particularly the ADC with respect to the sampling and acquisition of IQ data from the antenna. Is there a schematic available for the board or other documents on this or related topics?

[JerryAL]

Hi Eric

Unfortunately, it our policy to not provide schematics for our modules.  I would have to refer you to the NI 5640R Help file as well as the specification documents for the ADC and DACs for further information.

When we showed the demo at NIWeek, and a few other times, we use a simple RCA TV antenna which has an amplifier built in to amplify the signals for the NI 5640R’s ADC.  Without the amplifier, the NI 5640R doesn’t have enough dynamic range to pick the FM signals out of the back ground range.

Before using the demo, it would be a good idea to run the Spectrum Analyzer example first.  Set the DDC decimation to 100, that is the decimation that is used in the FM Demo program.  See if you are getting good FM signals with the antenna you are using and the location the antenna is at.

Another thing to consider for the demo is that the input section has an 80 MHz bandwidth, so the FM band is actually above this range.  But signals can still be acquired good enough for the demo.  Signals closer to the lower edge of the FM spectrum are best.  ~93 MHz.  Refer to the NI 5640R specifications for the Input Frequency Response.

Jerry

[EricTheRed]

Thanks Jerry, that cleared up one confusion I had about the board. I have a new question noe:

Where/How do I hook up an antenna to the board? Do I go through a port on the back through an sma cord? This is my first time working with antennas, so the most dumbed down answer would be the best.

Thanks a bunch!

Eric

[JerryAL]

Hi Erick

This question obviously depends on what kind of antenna you are using.

The simplest case is two wires (simple dipole), ranging to an antenna that has a coax or cable TV like connectors.  There are others as well.

In the case of an antenna that has a coax type connector, you need to find adaptors that will mate with the SMA connector on ADC0 on the NI 5640R. This is the kind we used for the demo.  The RCA powered antenna has a cable TV like connector that we used adaptors to connect it to the ADC0 SMA.

If you are trying just two wires, you’ll have to rig up something so that you can run one of the wires to the center pin of the SMA connector, and one to the ground/shield of the connector.

Jerry