Re: [Discuss-gnuradio] GRC squelch block with separate control signal?

[Iain Young, G7III]

Hi John et al,

First, my apologies for waking up this very old thread. Only the other 
night I had one of those "lightbulb" moments, as I have been trying to 
implement something similiar for a while myself.

On 07/09/11 12:58, John Ackermann N8UR 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 <address@hidden
> > <mailto:address@hidden>> 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.

Use a squelch block as normal. Use a function probe block to grab the
state of the "gate". Function name you want from the squelch block is
unmuted. Returns 1 if un-muted (I.E squelch open), 0 otherwise.

Use that variable as the input to a selector. If you are clever, your
selector has two inputs, 0 and 1. input 0 feeds a null source via a
throttle, 1 is your (squelched) input from your RX.

The output from the selector feeds the rest of your TX 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.

My own "design" is for a bi-directional cross-band repeater in both
directions,  sometimes called a talk-thru unit. Very important to
disable the TX on the same band when you have a signal :)

Another method would be to have an XML client get the values of the
squelch gate, and turn on/off each transmitter as appropriate by setting
the value of the TX selector.


Of course it being software, the possibilities are endless...multi
channel input and output...Multiple repeaters running on one URSP
[esp the USRP1 with two daughter boards....]


73s

Iain