回复： Re: spreading RF signal?

[MVK]

Hi,
I am trying to transmit a bit stream. Before doing demodulation, spreading the signal using user defined spreading code. In the receiving section also after demodulation, dispreading the output bit stream using the same user defined spreading code. But I am not getting the original bit stream. If I will acquire 5 to 10 times I will get original bit stream 1 or 2 times hardly. For these operations I am using PXI-5660 RF analyzer and PXI-5670 RF Signal generator. Using PXI-5670 transmitting the bit stream, than taking out the RF output from PXI-5670, feeding into PXI-5660. For these operations I am using onboard OCXO CLK, I am not using any other external or PXI back plane clock.
And one more dought for me. If i will change some perameter in the receiver section i am getting more number of bit stream. I mean for example if i am transmitting 6 bits say 110101, in my receiver output i am getting multiple times of my information(6 bits) i mean some 24 bits(4times) or 66 bits(11times) or 246 bits (41 times) like that.
With this i couldn't understand anything. what is going wrong in my vi. how to give the perameter , i mean what is the range of perameter should i give like Number of Symbols,Symbol Rate,TX Filter Alpha, and so on.

Please help me for this problem

For your better clarification please find the attachment which will give my vi.

Thank You
Regards,
Vijay

[Andy_Hinde]

Hello,
If you attach the VI we can look at it and see if there is any help we can offer.

[MVK]

Dear Andy Hinde,
I have already attached my VI with my enquiry. Any how i am sending onemore time. so please find the attachment.

[Andy_Hinde]

Hi Vijay,
Your original inquiry contained no attachments for some reason, so if you attached it for it did not make it into the post as you can see. In any case I received the VI now and have modified it to do what you want. You will need to upgrade to NI-RFSG 1.1 to use this.

Basically, I enabled differential PSK since your dmeodulated signal contained a 180 degree phase ambiguity due to having no sync parameters. I also added some triggering and sync bits to the spread message to help locate the actual message. Your 5670 will be triggering the 5660 over the PXI backplane on RTSI0 so if you have an 18 slot chassis you need to connect the PXI bus segments which contain the 5660 and 5670 in MAX. If you have an 8 slot chassis you don't need to do anything special.

Enjoy!

[xingbofeng]

hello

in your example ,it can get 6 bits stream exactly;if i transmit 7 bit stream or more .it can't receive the original bit stream. i want to transmit a user defined stream with any bit ,how can i do this .