GNU Radio 3.9 gr_modtool problem

[Ralf Gorholt]

Dear all,

on my Linux Mint (Ubuntu) box, I have installed and compiled GNU Radio
3.9 from source (master branch) as described here:

https://wiki.gnuradio.org/index.php/UbuntuInstall#Focal_Fossa_.2820.04.29

and here:

https://wiki.gnuradio.org/index.php/InstallingGR#From_Source

CMAKE_INSTALL_PREFIX is /usr.

GNU Radio compiles (without UHD and soapy support) and the tests are ok.
gnuradio-companion starts and everything seems ok. However, when I try
to create a new module with "gr_modtool newmod dl5eu", I get the error
message: ModToolException: Could not find gr-newmod source dir.

I have also tried what was necessary for Ubuntu 18:

$ cd /usr/share/gnuradio/modtool/templates/gr-newmod
$ sudo py3clean .

but this did not solve the problem.

With version 3.8 compiled from the maint-3.8 branch I don't have this
problem. Do you have an idea what I am doing wrong here?

Thank you very much.

Kind regards,

Ralf