diff --git a/charon_vna/io_.py b/charon_vna/io_.py
index bfa641a..a92b075 100644
--- a/charon_vna/io_.py
+++ b/charon_vna/io_.py
@@ -1,7 +1,6 @@
 from pathlib import Path
 
 import skrf as rf
-import xarray as xr
 from util import net2s
 
 
diff --git a/charon_vna/vna.py b/charon_vna/vna.py
index beb0144..ad34309 100644
--- a/charon_vna/vna.py
+++ b/charon_vna/vna.py
@@ -81,7 +81,7 @@ class Charon:
         # self.ctrl = ctx.find_device("ad9361-phy")
         # # raw ad9361 register accesss:
         # # https://ez.analog.com/linux-software-drivers/f/q-a/120853/control-fmcomms3-s-gpo-with-python
-        # # https://www.analog.com/media/cn/technical-documentation/user-guides/ad9364_register_map_reference_manual_ug-672.pdf
+        # # https://www.analog.com/media/cn/technical-documentation/user-guides/ad9364_register_map_reference_manual_ug-672.pdf  # noqa: E501
         # self.ctrl.reg_write(0x26, 0x90)  # bit 7: AuxDAC Manual, bit 4: GPO Manual
         # self._set_gpo(self.ports[0] - 1)
         # # TODO: init AuxDAC