# OP25 FSK4 Demodulator Error **URL:** \ **Category:** GNU Radio\ **Created:** [February 22, 2015, 8:08pm UTC](https://www.ruby-forum.com/t/op25-fsk4-demodulator-error/234299 "2015-02-22T20:08:53Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [February 22, 2015, 8:08pm UTC](https://www.ruby-forum.com/t/op25-fsk4-demodulator-error/234299/1 "2015-02-22T20:08:53Z")
I’m trying to get my OP25 flowgraph to work. I am having some issues with the FSK4 demodulator and the OP25 Decoder (Combined) blocks. When I run the flowgraph, I get the error “Exception: Could not find a FSK4 demodulator to use”. This happens whether I use the combined block, or the FSK4 Demodulator and the simple decoder. I have gr-baz, and gr-op25 installed. In the python shell, I have tried “from gnuradio import fsk4” and I get “cannot import name fsk4”. I did have to modify the op25.py file to point the import statement to the op25 library as discussed in [https://lists.gnu.org/archive/html/discuss-gnuradio/2014-07/msg00293.html](https://lists.gnu.org/archive/html/discuss-gnuradio/2014-07/msg00293.html) ---
**Author:** ![Brandon\_Lester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/43a26b/32.png) [@Brandon\_Lester](https://www.ruby-forum.com/u/Brandon_Lester)\ **Post date:** [February 22, 2015, 8:13pm UTC](https://www.ruby-forum.com/t/op25-fsk4-demodulator-error/234299/2 "2015-02-22T20:13:30Z")
Hi Brandon, which version of GNU Radio are you working with (`gnuradio-config --version`)? I’m not quite sure, but I think the porting of OP25 to GR 3.7 is still ongoing, so I’m not quite sure it’s supposed to work with current GNU Radio at this point. Greetings, Marcus ---
**Author:** ![Brandon\_Lester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/43a26b/32.png) [@Brandon\_Lester](https://www.ruby-forum.com/u/Brandon_Lester)\ **Post date:** [February 23, 2015, 1:32pm UTC](https://www.ruby-forum.com/t/op25-fsk4-demodulator-error/234299/3 "2015-02-23T13:32:45Z")
Hi Brandon, well, I haven’t tested OP25 on neither 3.6 nor 3.7, but the changes between the 3.6 and 3.7 class naming and module organization are the nr. 1 cause of OOT regressions; I’ve only fired up [osmocom.org](http://osmocom.org) and had a look on the OP25 to-do list, which says “Re-engineering and re-factoring to support GNURadio 3.7 and later.” Using 3.6 and 3.7 parallely works, but you have to make sure you don’t mix up things: I’d recommend you install both 3.6 and 3.7 in separate prefixes (you can install 3.7 into a prefix using pybombs, and follow the manual route to install 3.6.5 into another prefix [1]); then you can, by changing a few environment variables, use different versions. Pybombs will even give you a script you can use to modify paths to include your 3.7-prefix, and by changing a few lines in that, you can use a copy to do the same for your 3.6-prefix. Very handy for fiddling around with GNU Radio itself, without breaking everything that was built atop of a working GR installation 🙂 Greetings, Marcus [1] [http://gnuradio.org/redmine/projects/gnuradio/wiki/OldFAQ#Experts-only-How-can-I-deliberately-install-GNU-Radio-multiple-times-different-versions](http://gnuradio.org/redmine/projects/gnuradio/wiki/OldFAQ#Experts-only-How-can-I-deliberately-install-GNU-Radio-multiple-times-different-versions)