wireless video link example works with antenna only but not with SMA to SMA cable

[josephkirmani]

I am trying to run wireless video link example https://decibel.ni.com/content/docs/DOC-22728 . It works fine if I use install antennas on my Tx and Rx USRPs. But it does not work if I use SMA to SMA cable to connect Tx and Rx USRPs. Can somebody guide me what is the reason why it is only workng with antennas but not with SMA to SMA cable. 

Thanks 

JK

[ErikL]

Most likely over power and clipping. Please use a 30dB attenuator(s) or you may damage the hardware.

[josephkirmani]

Do you mean to say I should use attenuator both with Tx and Rx? 

[josephkirmani]

Also plz guide me where should I connect the attenuator?

[josephkirmani]

Let me add one more thing I am using two separate usrps. One is Tx and another is Rx.

[josephkirmani]

for connecting multiple USRP devices to each other, you must connect a 30 dB attenuator to the RF input (RX1 or RX2) of each receiving USRP device. 

So does it mean I need to conect 30 dB attenator to my RF input only right??

Please guide 

Thanks 

JK

[josephkirmani]

I connect the 30 dB attenuator at RF input port of Rx USRP. But it does not work completely.

Without connecting attenuator i was not able to receive any thing on my Rx VI although it shows waveform. But after connecting attenuator receiver some times receive text messages and some times not. Also it does not work at all for images and for video it works partially but gives some error related to memory full after few mins.

I want to know why this example works completely without any problem if I use antennas, and why it does not work perfectly if i use sma to sma cable for connecting transmit and receive usrps.

Please guide

Thanks 

JK

[ErikL]

The threshold for energy detection is a constant in the program. It probably has to do with different power levels. You can probably tweak the constant or use an energy detection algorithm to get better performance.

[josephkirmani]

Can you tell me in which VI its value is define. So that I can change the value from there.

[ErikL]