Think of the on/off part as a control stream consisting of 1's and
0's. Generate the control stream, and multiple the control stream by
the carrier stream.
Don't try to start and stop the graph or anything like that from
python.
You can probably generate the control stream with a
gr.vector_source_f([<my-pattern>], True) followed by a dumb
interpolator that will just replicate values.
my_pattern = [1, 1, 0, 0, 1, 0, ... ]
interp_factor = 1000 # scale the pattern up in time to match signal
ctrl_pattern = gr.vector_source_f(my_pattern, True)
ctrl_interp = gr.interp_fir_filter_fff(interp_factor, interp_factor*[1.0])
signal = <generate carrier>
mult = gr.multiple_ff()
sink = <something-downstream>
tb.connect(ctrl_pattern, ctrl_interp, (mult, 0))
tb.connect(signal, (mult, 1))
tb.connect(mult, sink)
One would think something like this would work, but I've noticed that even if you're sending 0's to your usrp sink, the transmitter still puts out some amount of power (plenty strong enough to be detectable via a spec-an). This power goes away if you disable the transmitter via software. Does anybody know anything about this phenomenon?
-Steven