Same output for different frequencies?

[Insiderbe]

Hi all,

I'm new to labview and the communication kit, therefore i'm currently testing the examples.

When opening the "Rx Continuous Sync or Async" example and running it I get the same output on the "power spectrum".
i"m checking different frequencies in the range of 1.2GHz to 6GHz

How is this possible while there's nothing being transmitted? -> checking with android app for wifi channels ( channels 1 and 8 are used, all the others aren't...) yet labview gives me the same output... ( attached file = 2GHz, the other one is a comparison of 5GHz, 2.412GHz and 2.484GHz)

hardware :

NI USRP N210 ( rev 4 )
CBX 1200-6000 MHz Rx/Tx (40 MHz)
VERT900 Antenna

connection via gigabit

PC: W7 64bit, i7-2600 @ 3.4GHz, 4Gb RAM

Thanks in advance

[tcap · Accepted solution]

Hey insiderbe,

I did some digging on the Ettus forum and found the following:
https://lists.gnu.org/archive/html/discuss-gnuradio/2010-08/msg00237.html
https://www.ruby-forum.com/topic/214890

I suspect that the spike that you are seeing at 0Hz is the DC offset that is introduced at the ADC of the USRP N210. We can confirm this by removing the antenna and terminating the RX. If the spike is still there, then it is a characteristic of the Analog Input circuitry.

Brian from Ettus recommends tuning your frequency slightly off from your signal of interest and using a High Pass Filter to remove the DC offset. I recommend looking at the second link for more information.

As far as getting the spike value across multiple different frequencies, I think that this is a property of the antenna being used. The VERT900 is only valid from 824-960MHz and 1710-1990MHz. Can you tune to one of those bands and test your power, while you have a known signal? Do you have another USRP or function generator to generate a known signal?

https://www.ettus.com/product/details/VERT900

My last concern is using the N210 with the CBX in LabVIEW Communications. According to the Readme, this is an unsupported hardware configuration meaning R&D has not tested the configuration, and we don't know how the configuration will perform.

http://download.ni.com/support/softlib//RF/NI%20USRP/15.0/niUSRP_readme.html

Thanks for making this post!

Regards,

[Insiderbe]

Tcap, 

thank you soo much for your response

1) The spike is there when the antenna is removed so that's the DC offset like you said 🙂

2) I was already afraid my antenna would be the problemmaker.... indeed, tuning in on frequencies in its range gives me another output ( see attached file: i found a signal on 1.8604 GHz... no idea what, maybe DCS-1800.  ( the daughterboard only support 1.2Ghz -> 6Ghz so i can't go lower.)

I will get another daughterboard and the corresponding antenna's tomorrowmorning ( we should need to have this in my school). Signal generators will also be for tomorrow, I only have walkie talkies 446MHz now...

Isn't there an antenna available with a wider range? 400Mhz -> 3GHz ?

Thanks for your help

[tcap · Accepted solution]

Hello Insiderbe,

Thanks for the quick reply.

I recommend looking into the antennas here:

https://www.ettus.com/product/category/Antennas

The LP0965 looks like your best option that we offer, bou can look at other 3rd party websites.

Regards,