Just looking at the async message interface for Qt GUI Frequency Sink.
The “freq” output (is that a PMT?) is always, it appears, in terms of
“display” frequency. Which is cool if you’re using the click-to-tune
output to modify (for example) a hardware source, but if you’re using it
to tune (for example) a freq-xlating FIR filter, there’s a
disagreement on semantics.
One could run the Frequency Sink in relative mode in this case. But it
seems like there should be more flexibility in dealing with the contents
of async messages, in situations where the message tag (“freq” in
this case) could have semantics that not everyone who takes such
a tag might agree on.
It should, I think, also be possible to turn such tags into variable
settings in GRC, but I couldn’t find any way to do so.