qt gui frequency sink in frequency hopping

Hi all,

I work on a Frequency Hopping (FH) Tx and Rx in the same grc flowchart in 3.7.13.4 in Ubuntu 16.04.

At the end of the Tx chain, I put a "Qt GUI Frequency Sink", but it just shows part of subchannels in the spectrum!!!

I changed its parameters especially "Update Period" but no change.

The very interesting point is that when I remove the Rx chain (lessen the complexity), it shows the spectrum of FH correctly!

I really wonder why.

Thanks,

AGD