[op25-dev] question about frequency correction messages from fsk4 demo

Stephen ctx50026 at centurytel.net
Sat Jun 23 20:02:49 UTC 2012


Hi,

I'm trying to do everything in c++ instead of using python. I've got it
working. Mostly. Well, sort of. I have a couple of questions about what
to do with the frequency correction messages coming from the fsk4demod
block.

I'm seeing a constant stream of frequency correction messages when there
is no signal present. They quickly cause the channel selection filter
I'm using to tune way off frequency.

If I don't process those messages I get voice output so I know
everything else is working. Some channels I tune to seem to work just
fine with out needing any tuning. But other times I see transmissions
where I don't get any voice output. I'm wondering if in those cases the
tuning is needed ?

In looking at the grc file it just subtracts the correction. When I look
at the uhd_p25_rx_gl.py file it's doing a calculation with the
correction and limiting it. Does one method work better than the other?

So, does anyone have any suggestions or any idea why I would be getting
a constant stream of the messages?

thanks,
Stephen
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