How to just send I data (No Q) using ni2920 USRP? (ASK modulation)

[sam2013ni]

Hi.  

 I am trying to send three level sequences as amplitude shift keying (ASK) modulation. my sequence has three state of (-1, 0 , 1). I am using ni2920 usrp to send carrier with amplitudes of -5v, zero, and +5v for each of the mentioned levels respectively (ASK) (Sample rate=25 or 50MS/s). to do that,  I saved a .txt file with voltages amplitudes in the PC and I am reading this .txt file and send them with USRP (I expect USRP to multiply these values with cos(carrier freq) and send it to its RF out port. However there some problems:

1. I am not sure about the order of data USRP expects to have when reading .txt file in terms of "I" and "Q".  Assume I am sending  0,0,-1,1,1,-1,0,... I have a txt file with 0,0,-5,5,5,-5,0 saved .. BUT every time my code reads this txt file , it assign a vector of <"I","Q"> pair at output of LAN cable instead of considering all numbers as "I" data. my problem is: How can I force USRP to just send I data (no "Q") ? (This is required since I am using ASK modulation)

2. when I read zero from txt file and send it, I expect to see zero level RF spectrum at output BUT according to my observation there is spectrum content of output RF when sending all zero sequences. How can I force USRP to send nothing (zero) when the bit=0? 

Any help is appreciated. Thanks.

[Kimchi-Taco]

Hi, please attach a simple version of your problem LabVIEW program so others may be able to work with it.  Also, you could take a look at Complex Functions>>Complex To Re/Im Function to split the I and Q data up.

Thanks,

[psisterhen]

1) You can send data to the device as complex double-precision data or binary I16 data.  If using the complex double type, just make the imaginary component of each complex sample 0 (Q is the imaginary componnent).  If using the binary I16 data, the samples are interleaved I, Q, I, Q, ... so just make every other sample 0.

2) Even when sending 0s for I and Q, if the device is tuned to a frequency and the output path is enabled, you may see some power at the carrier frequency that is basically leakage from the local oscillator.