[Discuss-gnuradio] Up Conversion Weirdness

[Thomas Schmid]

Hi Everyone,

I have some strange behavior of gnuradio while trying to do an
upconversion and multi-channel transmitter. I am currently trying to
have two packet transmitters send packets simultaniously on two
different radio channels. For this, I upconvert one of the
transmitters and add the two signals together. Following is the code
to connect the different blocks:

# interpolate the two transmitters
self.connect(self.packet_transmitter1, self.interpolator1)
self.connect(self.packet_transmitter2, self.interpolator2)
# upconvert the first transmitter)
self.connect(self.interpolator1, (self.multiplicator, 0))
self.connect(self.sin, (self.multiplicator, 1))
# add the two signals
self.connect(self.multiplicator, (self.adder, 0))
self.connect(self.interpolator2, (self.adder, 1))
# send the signal to the USRP
self.connect(self.adder, self.amp, self.u)
#self.connect(self.adder, self.filesink)

The code compiles, but I don't receive the messages on the other side.
Therefore, I did some tests to check the different parts. The
following connection works, i.e., the packet transmitter and its
interpolation can be received at the other side:

self.connect(self.packet_transmitter1, self.interpolator1)
self.connect(self.interpolator1, self.amp, self.u)

Now, if I add the following, it suddenly doesn't work anymore, even
though the added connections should not affect the path to the USRP:

self.connect(self.packet_transmitter1, self.interpolator1)
self.connect(self.interpolator1, (self.multiplicator, 0))
self.connect(self.sin, (self.multiplicator, 1))
self.connect(self.interpolator1, self.amp, self.u)
self.connect(self.multiplicator, self.filesink)

Does anyone know why this could happen?

Thanks a lot,

Thomas