________________________________ From: Eric Blossom <e...@comsec.com> To: w w <biscuitk...@gmail.com> Cc: discuss-gnuradio@gnu.org Sent: Wednesday, March 18, 2009 4:30:04 PM Subject: Re: [Discuss-gnuradio] DBPSK and Carrier Suppressed or Not? > If I take the output of the modulator and go directly to the demod thru the > channel filter, data flows just fine(bypassing the usrp). > > I'm only using one usrp and taking the output of the TX via coax and going > into the RX side...that shouldn't make a difference should it? > Any thoughts? > > Cheers, > Jody Before writing your own, did you take a look at the implementation of dbpsk that's already in the tree? See the -m dbpsk option below $ ./benchmark_tx.py --help Usage: benchmark_tx.py [options] Options: -h, --help show this help message and exit -m MODULATION, --modulation=MODULATION Select modulation from: cpm, d8psk, qam8, dbpsk, dqpsk, gmsk [default=gmsk] -s SIZE, --size=SIZE set packet size [default=1500] -M MEGABYTES, --megabytes=MEGABYTES set megabytes to transmit [default=1.0] --discontinuous enable discontinous transmission (bursts of 5 packets) --from-file=FROM_FILE use file for packet contents -f FREQ, --freq=FREQ set Tx and/or Rx frequency to FREQ [default=none] -r BITRATE, --bitrate=BITRATE specify bitrate. samples-per-symbol and interp/decim will be derived. -w WHICH, --which=WHICH select USRP board [default=0] -T TX_SUBDEV_SPEC, --tx-subdev-spec=TX_SUBDEV_SPEC select USRP Tx side A or B --tx-amplitude=AMPL set transmitter digital amplitude: 0 <= AMPL < 32768 [default=12000] -v, --verbose Expert: -S SAMPLES_PER_SYMBOL, --samples-per-symbol=SAMPLES_PER_SYMBOL set samples/symbol [default=none] --tx-freq=FREQ set transmit frequency to FREQ [default=none] -i INTERP, --interp=INTERP set fpga interpolation rate to INTERP [default=none] --log Log all parts of flow graph to file (CAUTION: lots of data) --use-whitener-offset make sequential packets use different whitening --excess-bw=EXCESS_BW set RRC excess bandwith factor [default=0.35] (PSK) --no-gray-code disable gray coding on modulated bits (PSK) --bt=BT set bandwidth-time product [default=0.35] (GMSK) -B FUSB_BLOCK_SIZE, --fusb-block-size=FUSB_BLOCK_SIZE specify fast usb block size [default=0] -N FUSB_NBLOCKS, --fusb-nblocks=FUSB_NBLOCKS specify number of fast usb blocks [default=0] Hi, w w You donot need to add other channel filters because there is a rrc filter as well as a channel filter in DEMOD. Pleas note that: you should decrease the TX power before connecting them via coax. On Wed, Mar 18, 2009 at 02:55:41PM -0400, w w wrote: > I'm putting together a DBPSK Tx and Rx and running into problems when the > modulated signal hits the USRP. When I receive the signal on the USRP > there's a very pronouced carrier.....I've confirmed with a spectrum analyser > that the signal on the FFT is the one that I'm recieving. It seems to me > that the sidebands should be close to the highest amplitute and the carrier > should be suppressed.....is this correct? Shouldn't the output of the DPSK > modulator FFT plot look very similar to the FFT plot on the RX side of the > usrp? I'm modeling the block connections after the benchmark samples in > the digital example section. I put a channel filter inline with the usrp > and the dpsk demod block just like the example.....do I need to put more > filtering in place to suppress the carrier? If so, do you have any > examples? Bill _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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