[USRP-users] Full Duplex w/ X310 & UBX-160

mleech at ripnet.com mleech at ripnet.com
Wed Mar 30 13:31:58 EDT 2016


 

If you transmit all zeros, with the TX gain cranked down, do you get
"proper" RX? 

In full-duplex, the RX2 port is used for the RX chain, and TX/RX for the
TX chain, always. otherwise, your RX LNA would go "poof" as soon as you
transmit significant power. 

So you have two antennae setup? How far apart are they? Small-signal RF
amplifiers (like LNAs) have only so much linearity headroom, so if
there's a 1GHz signal screaming in the LNA's ear, it'll be hard for the
rest of the system to "see" other frequencies. 

On 2016-03-30 13:18, Dave NotTelling wrote: 

> I tuned the RX side to simply pick up some known signals in the area. 
> 
> On Wed, Mar 30, 2016 at 1:07 PM, <mleech at ripnet.com> wrote:
> 
> If you're transmitting at a frequency other than you're receiving at, why would you expect to be able to receive it? I don't understand. 
> 
> On 2016-03-30 13:02, Dave NotTelling wrote: 
> Oh, sorry, I meant that I no longer see the GFSK transmission. I also should have added that I don't get a correct spectrum from the RX side *at all*. If I disable one of the two chains (disable all TX or RX) then everything works fine. 
> 
> On Wed, Mar 30, 2016 at 1:00 PM, <mleech at ripnet.com> wrote:
> 
> What do you mean by "it all breaks down"? Error messages? 
> 
> On 2016-03-30 12:55, Dave NotTelling wrote: 
> Marcus, 
> 
> This is odd then. Please see the attached for my example flow graph in GNU Radio. The basics are that I am transmitting a GFSK (just for giggles) on 1.001 GHz and receiving on 900 MHz. When the graph starts up, the TX side is working properly. I can tell this by looking at the output of my B200 which is tuned to 1.001 GHz. The moment I change a parameter (RX/TX gain/freq) it all breaks down. Is this possibly an issue with the X300/X310 UHD driver and/or GNU Radio gr-uhd? Or am I just doing something stupid? 
> 
> Thank you! 
> 
> -Dave 
> 
> On Wed, Mar 30, 2016 at 12:22 PM, <mleech at ripnet.com> wrote:
> 
> The RX and TX synthesizers are totally separate on the UBX, so you can frequency-split however you want. 
> 
> The larger the split, the easier it will be to prevent de-sense between TX and RX, since it would be easy to, for example, insert a notch filter for your TX band into the RX path, etc. 
> 
> On 2016-03-30 11:18, Dave NotTelling via USRP-users wrote: 
> 
> Can I transmit at say 100 MHz while simultaneously receiving at say 1 GHz? If so, can I also use different sampling rates between the TX and RX paths? Are there any existing examples of how to do simultaneous TX and RX in GNU Radio? 
> 
> If this is not possible, then what is the max frequency difference? I was assuming that if I were transmitting at 1 GHz, then I could tune the RX side up and down by half the master clock rate. 
> 
> Thank you! 
> 
> -Dave 
> 
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