Gmsk transmit woes


#1

Hello,

I’m having a curious problem that I’d like to figure out. What I’m
trying
to do is to have two different gmsk packet sources, modulate them on
different frequencies, add these signals together and then transmit them
simultaneously (with their destination being two separate usrp’s tuned
to
the different frequencies). Here is a sketch of what I have so far:

self.packet_transmitter1 = blks.gmsk2_mod_pkts(…)
self.packet_transmitter2 = blks.gmsk2_mod_pkts(…)

self.chan_filt1 = gr.freq_xlating_fir_filter_ccc(…freq1…)
self.chan_filt2 = gr.freq_xlating_fir_filter_ccc(…freq2…)

self.adder = gr.add_cc()

fg.connect(self.packet_transmitter1, self.chan_filt1, (self.adder,0))
fg.connect(self.packet_transmitter2, self.chan_filt2, (self.adder,1))

fg.connect(self.adder, self.amp, self.u)

for now, I have both the xlating_fir’s as all-pass filters, just to take
advantage of their frequency translating. The strange problem is that
when
I run the script, it stalls; the code gets 2 dots into the transmitting
and
then stops, and I have to ctrl-z (ctrl-c doesn’t even work). What is
possibly going wrong?

Thanks!

-Michael F.-


#2

Michael F. wrote:

self.packet_transmitter2 = blks.gmsk2_mod_pkts(…)

for now, I have both the xlating_fir’s as all-pass filters, just to
take advantage of their frequency translating. The strange problem is
that when I run the script, it stalls; the code gets 2 dots into the
transmitting and then stops, and I have to ctrl-z (ctrl-c doesn’t even
work). What is possibly going wrong?

Thanks!

-Michael F.-
Michael,

Take a look at my reply to “up-conversion weirdness” on Oct. 27, 2006.
It seems like this is the same problem due to incorrect sampling rates.
Hopefully, this will help.

Tom