Here's how to get the N321's LO sharing to work in GNURadio 3.9 with UHD4.1.0.5

Currently there's no way to use LO sharing with the N321 in gr-uhd.

The N321 uses an RF Distribution board which has port terminations that need to be switched to active outputs when the LO is exported. This isn't accessible in gr-uhd.

In order to access the LO distribution enable commands shown here:
https://kb.ettus.com/USRP_N320/N321_LO_Distribution#UHD_LO_Distribution_Commands

a function needs to be added to gr-uhd

All this code below is taken from here:
https://github.com/daniestevez/uhd/commit/0a6da1a3fd5839b862cac740ed702923ed21b096
https://github.com/daniestevez/gnuradio/commit/f9909bade86045f379f83001de27317cc261807f

with the rx switched for tx and source switched for sink

i also did not modify any UHD code making this a fix that requires ONLY modifying gr-uhd

usrp_sink_impl.cc

void usrp_sink_impl::set_tx_lo_dist(bool enabled,

const std::string& name,

size_t chan)

{

#ifdef UHD_USRP_MULTI_USRP_TX_LO_CONFIG_API

_dev->get_tree()->access<bool>("/blocks/0/Radio#0/dboard/tx_frontends/0/los/lo1/lo_distribution"/ ::uhd::fs_path(name) / "export").set(enabled);

#else

throw std::runtime_error("not implemented in this version");