On Wed, Sep 7, 2011 at 7:58 AM, John Ackermann N8UR <j...@febo.com> wrote:
> > > Tom Rondeau said the following on 09/06/2011 11:28 AM: > >> On Tue, Sep 6, 2011 at 10:22 AM, John Ackermann N8UR <j...@febo.com >> <mailto:j...@febo.com>> wrote: >> >> I want to implement the equivalent of a carrier-operated relay -- a >> squelch block that provides an "on" signal at a threshold input >> signal level, which then passes or blocks data at some point further >> downstream rather than right at the point where the sensing is >> happening. >> >> Are there GRC blocks that will allow this? >> >> Thanks, >> >> John >> >> >> >> John, >> Yes, look in "Level Controls," there is a "Simple Squelch," "Standard >> Squelch," and "Power Squelch" as well as a simple "Threshold." You'll >> have to look closer into this blocks to find out how they work. >> >> Tom >> > > Hi Tom -- > > The challenge is that the three squelch blocks all sense and switch the > data stream at the same point -- the input signal is passed or not based on > its level. What I need instead is to sense the stream at one point, and use > that information to switch a different data stream. > > I could picture two blocks -- one that sets (and updates) a boolean > variable based on the current signal level, and another that switches a > separate sample stream based on whether that variable is true or false. > Does GRC support message passing between blocks in that fashion? > > The practical example is an FM repeater where the transmitted signal is > turned on only when the received signal level exceeds a threshold. > > Thanks, > > John > You can use a message for this, or you can use the stream tagging interface where a message is tagged specifically to a sample number. It's a way of passing synchronous messages where the message passing interface doesn't. The problem is, you really have to work inside of the C++ code to get to the stream tags, so you won't be able to work in GRC for it. Tom
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