Re: Packet TX and RX on E312

[Marcus D. Leech]

On 06/25/2020 12:44 PM, Cameron Matson wrote:
> I moved my setup from e312s to n310s so that I could run the 
> flowgraphs with the gui blocks to help with debugging.  It looks like 
> the phase is off at the RX as the constellation gui from the USRP (the 
> one before the Packet Rx block) is rotating.  I'm able to adjust the 
> magnitude of the IQ data by playing with the tx and rx gain, but I 
> can't get the phase to lock.
>
> What are some of the knobs I can turn to help the Packet Rx block 
> detect the signal given the phase offset?
>
> Thanks,
> Cameron
So an independent RX and TX will NOT be operating on exactly the same 
frequency.  This means that for many types of phase-sensitive
  modulation, the RX needs to track the phase rotation caused by the 
(small) frequency difference.  This is just standard modem
  design, and you'll need to look at carrier-tracking with PLLs, etc.

There are a plethora of folks on here more adept than I at suggesting 
which PLL approaches to take, but suffice it to say, any modem RX design
  that doesn't include some kind of PLL-based tracking is "born flawed".